CHAPTER
17
Morphology,, Characters, and
the Interrelationships of
Basal Sarcopterygians
RICHARD CLOUTIER
URA 1365 du CNRS
Université des Sciences et Technologies de Lille
Sciences de la Terre
59655 Villeneuve d'Ascq, France
PER ERIK AHLBERG
Palaeontology
The Natural History Museum
Cromwell Road, London SW7 5BD, United Kingdom
Department of
daim for it than that, as it "seems to do least injustice
to knowledge in its present state, it is proposed as a
model for future discussion" (Andrews, 1973, p. 137).
The rest of the decade saw graduai progress in sarcopterygian phylogenetics. Miles (1975) used parsimony arguments to place lungfishes and "crossopterygians" side by side as sister-groups in the clade
Sarcopterygii. He included the Tetrapoda within
Crossopterygii but did not consider the possibility that
the latter group might be paraphyletic relative to the
Dipnoi. However, in a subsequent paper (Miles, 1977)
he placed the Actinistia as sister-group to the
Dipnoi + Choanata. Schultze (1977) applied cladistic
principles to the distribution of fin and limb characters
among the Sarcopterygii.
At the 26th Symposium of Vertebrate Palaeontology and Comparative Anatomy held in 1978 at Reading, England, Gardiner presented a paper on sarcopterygian cladistic phylogeny which started a series of
methodological debates. As a response to a comment
by Parrington, Patterson confirmed—in support of
Gardiner's arguments for a cladistic view of relationships—that a lungfish shares more characters with a
cow than with a salmon. "The salmon, the lungfish,
and the cow" soon became familiar as a classic example of a three-taxon statement. The debate was continued in the pages of Nature (Halstead, 1978; Halstead
et al., 1979; Gardiner et al., 1979).
I. Historical Background)
A new chapter in sarcopterygian systematics
opened in 1970 when Schultze (1970) published a brief
overview of sarcopterygian tooth structure which explicitly used the distribution of derived characters to
delineate monophyletic groups and to argue for tetrapod monophyly. Three years later, Andrews (1973)
produced the first attempt at an overall cladistic analysis of the sarcopterygian fishes. Although it retained
certain characteristics of previous analyses, such as
a priori separation of lungfishes and tetrapods from
"crossopterygians" and a tendency to search for "key
characters," it centered on a wide-ranging and thorough review of character state distributions and character polarities. Andrews (1973) concluded that character incongruence and thus evolutionary parallelism
was rife among the "crossopterygians," but that the
skull roof pattern might provide a reasonable guide
to their relationships. On this basis she presented
fully resolved phylogeny (Fig. la) which divided the
Crossopterygii into Binostia (actinistians and porolepiforms) and Quadrostia (osteolepiforms, rhizodonts,
and onychodonts). However, she made no greater
1 A11 generic taxa referred in the text are extinct with the exception
of Polypterus, Latimeria, Protopterus, Lepidosiren, and Neoceratodus.
INTERRELATIONSHIPS OF FISHES
445
Copyright © 1996 by Academic Press, Inc.
Ail rights of reproduction in any form reserved.
446
RICHARD CLOUTIER AND PER ERIK AHLBERG
A
—Osteolepif ormes
t.s
- - - Eus thenop ter o
Actinistia
o
rcs
Dipnoi
Rhizodontif ormes
Actinistia
Porolepiformes
C3)
LPowichthys
— Porolepiformes
Onychodontiformes
—o
Youngolepis
,r)
Coelacanthiformes
Dipnoi
—Osteolepiformes
Porolepiformes
Tetrapoda
Dipnoi
Actinistia
—Tetrapoda
Onychodontia
Actinistia
_r_Tetrapoda
— On yc ho don ti or mes —
Panderichthyidae
Povvichthys
Youngolepis
Porolepif ormes
Osteolepiformes
Osteolepif ormes
Rhizodontida
Porolepiformes
Powichthys
Youngolepis
Panderichthyidae
—Tetrapoda
_J—Diabolepis
Dipnoi
FIGURE 1 Previously published sarcopterygian phylogenies. (A) Andrews (1973); note
that this phylogenetic hypothesis does not consider either the Dipnoi or the Tetrapoda.
(B) Rosen et al. (1981); a pattern-cladistic approach with fossil taxa (dashed unes) inserted
after the analysis of the Recent forms. Eusthenopteren occupies a basal position, far removed
from the Tetrapoda. (C) Panchen and Smithson (1987); (D) Schultze (1987); (E) Ahlberg
(1991b). Phylogenies (C)—(E) are based on fossil and Recent data. Osteolepiforms and
"panderichthyids" (=elpistostegids; see text) consistently group with tetrapods, but otherwise there is little agreement between the three.
"The Terrestrial Environment and the Origin of Land
Vertebrates" (edited by A. L. Panchen), published in
1980, gave a snapshot of the growing influence of
cladistic methodology on sarcopterygian phylogenetics. With hindsight the two most significant papers
are those of Patterson (1980) and Gardiner (1980). The
former was a powerful critique of noncladistic approaches to the problem of tetrapod origins, while the
latter presented a cladogram where lungfishes were
the living and fossil sister-group of tetrapods, and
"crossopterygians" were paraphyletic. Forey (1980)
used a pattern-cladistic approach to argue that Latirneria is a sarcopterygian, the sister-group of Dipnoi +
Tetrapoda, rather than a chondrichthyan.
The points made by Patterson (1980), Gardiner
(1980), and Forey (1980) were developed further by
Rosen et al. (1981) in a provocative paper (Fig. lb)
which succeeded in starting a vigorous debate. The
17. Interrelationships of Basal Sarcopterygians following years saw a surge of publications on this
topic, many of them couched as rebuttals of Rosen
et al. but nevertheless characterized by an explicitly
cladistic approach (Holmes, 1985; Jarvik, 1980; Long,
1985, 1989; Maisey, 1986a; Panchen and Smithson,
1987; Schultze, 1981, 1987, 1991, 1994; Ahlberg, 1989,
1991b; Cloutier, 1990, 1991a,b; Chang, 1991a,b; Chang
and Smith, 1992; Young et al., 1992; Ahlberg and Milner, 1994). Much of the interest focused on the threetaxon problem of the living groups and on the position
of the Osteolepiformes (Figs. lc— 1 e). Forey (1987) and
Forey et al. (1991) continued to build on the work of
Rosen et al.
Alongside the systematic reviews came a sequence
of descriptive works (Vorobyeva, 1977; Jarvik, 1980;
Campbell and Barwick, 1982a,b, 1984, 1987, 1988;
Chang, 1982, 1991b; Chang and Yu, 1984; Andrews,
1985; Schultze and Arsenault, 1985; Long, 1989; Ahlberg, 1989; Ahlberg et al., 1994; Clack, 1989, 1994a,b;
Coates and Clack, 1990, 1991; Vorobyeva and
Schultze, 1991) which significantly expanded the data
set available for phylogenetic analysis. The development of computer programs for phylogenetic inference ushered in the present stage of the debate, characterized by exhaustive analyses of large data sets
(Cloutier, 1990, 1991a,b; Ahlberg, 1991b; Forey et al.,
1991; Lebedev and Coates, 1995; Schultze, 1994;
Schultze and Marshall, 1993). On a parallel front, several workers have approached the three-taxon problem of lungfish, coelacanth, and tetrapod relationships from a molecular perspective (Meyer and
Wilson, 1990; Gorr et al., 1991; Stock and Swofford,
1991; Hedges et al., 1993). At present the bulk of the
molecular evidence favors a lungfish—tetrapod sistergroup relationship (Meyer, 1995).
The last 20-odd years of research into sarcopterygian phylogeny have produced an enormously enlarged data base as well as substantial improvements
in phylogenetic methodology and practice. No complete phylogenetic consensus has developed, but several significant and probably permanent changes of
opinion have taken place:
There is almost universal agreement (but see
Jarvik, 1980) about the status of the Sarcopterygii as
a clade and about the characters which define the
group (Rosen et al., 1981; Schultze, 1987; Panchen and
Smithson, 1987; Ahlberg, 1991b).
Placement by Rosen et al. (1981) of the Dipnoi
as the living and fossil sister-group of the Tetrapoda
has flot generally found favor. Most paleontologists
favor the "traditional" osteolepiform—tetrapod relationship, redefined in terms of shared derived characters (Schultze, 1987; Panchen and Smithson, 1987;
447
Long, 1989; Cloutier, 1990, 1991a; Ahlberg, 1991b;
Vorobyeva and Schultze, 1991; Young et al., 1992;
Ahlberg and Milner, 1994). The majority of these authors remove the elpistostegids ("panderichthyids";
see below) from osteolepiforms and regard the osteolepiforms as the sister-group of the clade
[elpistostegids + tetrapods]. Panchen and Smithson
(1987), however, place the elpistostegids within the
osteolepiforms. The main nonparticipants in this consensus are Chang (1991b), who regards tetrapods as
the sister-group of ail other sarcopterygians, and
Forey et al. (1991), who continue to place the lungfishes as the living and fossil sister-group of tetrapods.
A number of authors have come to view the
Porolepiformes and the Lower Devonian genera Youngolepis and Powichthys as immediate relatives of the
Dipnoi (Maisey, 1986a; Ahlberg, 1989, 1991b; Cloutier,
1991b; Chang, 1991a,b; Chang and Smith, 1992). This
is linked with the recognition of Diabolepis (Chang and
Yu, 1984) as a primitive lungfish (Fig. le), although
some authors (Forey et al., 1991) accept the latter proposition without agreeing with the former. Another
group of workers (Schultze, 1987; Panchen and Smithson, 1987; Long, 1989) place the porolepiforms and
Youngolepis as separate plesions on the stem to Eosteolepiforms + tetrapods] (Figs. lc and 1d).
As regards the three-taxon problem of coelacanths, lungfishes, and tetrapods, most recent paleontological analyses favor a lungfish—tetrapod sistergroup relationship (Maisey, 1986a; Panchen and
Smithson, 1987; Cloutier, 1990, 1991a; Ahlberg, 1991b;
Trueb and Cloutier, 1991; Forey et al., 1991). However,
there is also support for a Recent sister-group relationship between coelacanths and tetrapods (Schultze,
1987; Long, 1989; Vorobyeva and Schultze, 1991) or
between coelacanths and lungfishes (Chang, 1991b).
While it is heartening to see emerging areas of
agreement, the substantial remaining disputes cannot
be ignored. These are largely due to differences in
character interpretation and scope. Thus, the reassertion of the osteolepiform—tetrapod relationship is directly linked to the rejection of the interpretation of
Rosen et al. (1981) of osteolepiform snout anatomy
in favor of Jarvik's (1942, 1980) model. Many of the
characters used by Maisey (1986a), Ahlberg (1989,
1991b), Chang (1991a,b), and others to link porolepiforms and lungfishes are ignmed by Schultze (1987)
and Panchen and Smithson (1987).
Our purpose in this chapter is to review the state
of knowledge for ail the major sarcopterygian groups
and to present a phylogenetic analysis based on a
large data set. Our respective contributions in part
reflect our slightly different fields of research. Cloutier
448
RICHARD CLOUTIER AND PER ERIK AHLBERG
provided the information about actinistians, onychodonts, and dipnoans, while Ahlberg was the principal
contributor on tetrapods, elpistostegids, porolepiforms, and Y oungolepis + Powichthys. The character
matrix represents our shared knowledge and derives
from several sources (e.g., Ahlberg, 1991b); however,
the largest component was the previously unpublished character matrix from Cloutier's Ph.D. thesis
(1990). For this reason, and because he performed
the phylogenetic analysis and interpretation, Cloutier
takes the formai position as principal author. It was
a salutary experience to discover, during the preparatory stages of this collaboration, that there were considerable and sometimes irreconcilable differences between our character tables. Some of these were due
to difficulties with poorly preserved specimens, but
in other cases the disagreement was purely one of
interpretation. This may be symptomatic of the debate
as a whole. The significance of these problems is considered in more detail in the Discussion.
or. dei
‘11811.
- -"Ideil
.114
II. The Principal Sarcopterygian Groups
The following section attempts to summarize most
of our knowledge of sarcopterygian morphology and
diversity (Fig. 2). The major omission is the tetrapod
crown group, which is not discussed in detail; its diversity is so great that any attempt at a systematic
overview would swamp the rest of the paper, and we
felt that a full account of the known stem tetrapod
genera was more important and timely. Detailed trea tments of crown tetrapod systematics can be found
Carroll (1988) and elsewhere.
A. A ctinistia
The Actinistia (=Coelacanthi, Coelacanthia, Coelacanthiformes, Coelacanthii, Coelacanthina) include
approximately 125 species belonging to 50 genera
(Cloutier and Forey, 1991). They range in time from
the Middle Devonian to Recent and reached their maximum of diversity during the Lower Triassic (Cloutier
and Forey, 1991). However, they are known from the
fossil record only from the Middle Devonian to the
Upper Cretaceous. The earliest actinistian known is
Euporosteus eifelianus from the Givetian of Germany
(Stensiô, 1937), whereas the youngest fossil species
is Megalocoelacanthus dobiei from the latest Campanian
to middle Maastrichtian of New Jersey (Schwimmer
et al., 1994). Orvig (1986) identified a fragment of bone
possibly referrable to an actinistian, on histological
characteristics, from the Paleocene of southern Swe-
FIGURE 2 A representative range of early osteichthyans. (A) The
actinopterygian Mimia toombsi (after Gardiner, 1984). (B)—(I), Sarcopterygii; (B) the actinistian Rhabdoderma elegans (after Forey, 1981);
(C) the onychodont Strunius walteri (after Jessen, 1966); (D) the
tetrapod Ichthyostega groenlandica (modified from Jarvik, 1952, 1980);
(E) the elpistostegid Panderichthys rhombolepis (after Vorobyeva and
Schultze, 1991); (F) the osteolepiform Osteolepis macrolepidotus (after
Jarvik, 1948); (G) the rhizodont, ?Strepsodus anculonamensis (modilied from Andrews, 1985); (H) the porolepiform Glyptolepis paucidens
(original); (I) the dipnoan Dipterus valenciennesi (after Ahlberg and
Trewin, 1995). Not to scale. Except for Rhabdoderma and Strepsodus,
which are of Carboniferous age, ail these genera date from the
Middle-Upper Devonian (Eifelian—Famennian).
den. Latimeria chalumnae is the only living representai:ive of this group and it has been found only in the
Comoros Archipelago, Mozambique Strait, and Chalumna River (Republic of South Africa).
Although the monophyly of the Actinistia has
never been questioned, the diagnosis has been addressed repeatedly (Andrews, 1973; Forey, 1981, 1984;
Maisey, 1986a; Panchen and Smithson, 1987; Cloutier,
1991a,b, 1996a). The Actinistia is monophyletic based
17. Interrelationships of Basal Sarcopterygians
on the following synapomorphies (Cloutier, 1996a):
(1) absence of maxilla, (2) absence of surangular, (3)
absence of branchiostegal rays, (4) absence of submandibulars, (5) presence of rostral organ, (6) numerous
supraorbitals, (7) presence of extracleithrum (absent
in the Diplocercidae), (8) triangular entopterygoid, (9)
short dentary, (10) dorsal margin of angular elevated
nto a process, (11) coronoid IV oriented vertically, and
(12) anterior position of anterior dorsal fin. Characters
2 and 10 are possibly dependent characters, characters
1 and 9 are homoplastic with respect to the Dipnoi,
character 3 is homoplastic with respect to the Onychodontida, and character 4 is homoplastic with respect
to the Tetrapoda.
Three additional characters are considered as potential synapomorphies for the actinistians (Cloutier,
1991a,b), but their condition remains unknown or
unclear in Miguashaia bureaui: (13) presence of ventral
process of lateral rostral, (14) tandem jaw articulation, and (15) posteriorly expanded U-shaped urohyal.
In addition to the characters listed above, Forey
(1991) considered the following three characters as
synapomorphies of the Actinistia: (1) second dorsal
and anal fin lobes both contain a skeleton of several
segments which resemble the endoskeletons of the
paired fins, (2) head divided by a prominent intracranial joint in which the otico-occipital part of the neurocranium extends anteriorly to form a track-andgroove joint with the basisphenoid, and (3) small
premaxilla. The first character is probably absent in
Miguashaia bureaui; although the median fin endoskeletons are flot preserved, the lack of a posterior
dorsal fin lobe (and the very slight lobation of the
anal fin) suggests that the endoskeletons were of a
generalized sarcopterygian pattern (Ahlberg, 1992a);
this character might be a synapomorphy of the clade
[Actinistia except Miguashaial (Cloutier, 1996a). The
condition of the second character cannot be determined in M. bureaui; thus, it remains a potential
synapomorphy of the group. The size of the premaxilla in Miguashaia is comparable to that of other
sarcopterygians.
Schultze (1973) proposed Miguashaia bureaui (middle Frasnian, Escuminac Formation, Québec, Canada)
to be the most primitive actinistian. According to
Cloutier (1991a,b, 1996a), Miguashaia is an actinistian
because it shares the aforementioned derived characters with other actinistians, and within this clade it is
the sister-taxon of the rest of the group. The clade
[Actinistia except Miguashaia] is characterized by the
following characters: absence of intertemporal, lacrimal fused with jugal, otic canal passing in postpari-
449
etal, unbranched distal ends of lepidotrichia, tail
notochord straight and horizontal, epichordal and hypochordal lepidotrichia symmetrical, and presence of
a supplementary caudal fin.
Interrelationships among actinistians have been investigated recently by Cloutier (1991a,b) and Forey
(1991). Although there are minor disagreements between them (notably the position of the Coelacanthidae), both phylogenies are strongly asymmetrical and
have good stratigraphic correlation. Most actinistian
classifications fail to reflect the phylogeny of the
group, but Schultze (1993) erected a classification
which reflects Cloutier's (1991b) phylogeny.
Miguashaiidae Schultze 1993 is a monospecific family containing the middle Frasnian Miguashaia bureaui from the Escuminac Formation of Québec.
The anatomy of Miguashaia is fairly well known
(Cloutier, 1996a) with the exception of the neurocranium, gill arches, and axial skeleton. An isolated scale from the Givetian of Latvia is referred
to the genus Miguashaia (Cloutier et al., 1996).
Miguashaia does flot belong to the Coelacanthidae
as suggested by Carroll (1988).
Diplocercidae Stensiô 1922 is a monogeneric family
including fewer than 10 taxa of Deyonian and
Lower Carboniferous age. Nesides Stensiô has
been synonymized with Diplocercides by Cloutier
and Forey (1991). Traditionally the genera Euporosteus and Chagrinia have been incorporated
within the Diplocercidae; however, based on
their phylogenetic position (Cloutier, 1991a,b)
they are removed from this family. Diplocercides
is the only Devonian actinistian in which the neurocranium has been studied in detail (Jarvik,
1954, 1964; Bjerring, 1993).
Hadronectoridae Lund and Lund 1984 is a family
originally created to include the three Namurian
actinistians Allenypterus, Hadronector, and Polyosteorhynchus from the Heath Formation (Bear
Gulch fauna), Montana. Lund and Lund (1985)
provided detailed descriptions of the anatomy of
these genera. Cloutier (1991a) excluded Allenypterus in order to keep the family monophyletic.
The presence of a series of bifurcating supraorbital pores associated with the supraorbital sensory canal corroborates the monophyly of this
clade (Cloutier, 1991a).
"Rhabdodermatidae" Berg 1958 is a paraphyletic
family including mainly Carboniferous genera
(e.g., Rhabdoderma and Caridosuctor). The Carboniferous Rhabdoderma elegans is the best known
representative of this group (Forey, 1981).
450
RICHARD CLOUTIER AND PER ERIK AHLBERG
Laugiidae Berg 1940 includes the genera Laugia and
Coccoderma and ranges in time from the Lower
Triassic to the Lower Cretaceous. In contrast to
its classification in Schultze (1993), Synaptotylus is
excluded from this family in order to respect the
monophyly of the Laugiidae.
Whiteiidae Schultze 1993 is a family created to include the Triassic genus Whiteia from Madagascar
and western Canada. A great deal of the anatomy of these forms remains to be redescribed,
on the basis of available material. This might require a reidentification of the North American
species (R. Cloutier, personal observation).
Coelacanthidae Agassiz 1843 is a family in which,
to keep its monophyly, Cloutier (1991b) included
all actinistians sharing the common ancestor of
Coelacanthus and Latimeria. However, Schultze
(1993) restricted the definition of the family to include Coelacanthus, Axelia, Wimania, and Ticinepomis. The phylogenetic position as well as the
definition of the Coelacanthidae differ between
Cloutier's (1991b) and Forey's (1991) hypotheses.
Mawsoniidae Schultze 1993 includes Triassic and
Jurassic genera (Alcoveria, Diplurus, Chinlea, Mawsonia, and Axelrodichthys) forming a clade which
is the sister-group to the Latimeriidae (Cloutier,
1991b; Forey, 1991). Diplurus newarki (Schaeffer,
1952) and Axelrodichthys araripiensis (Maisey,
1986b) are the best known representatives of this
family.
Latimeriidae Berg 1940 is a family including the
only living representative (Latimeria chalumnae) as
well as a few Jurassic and Cretaceous genera (Holophagus, Undina, Libys, Macropomoides, and Macropoma). Lambers (1992) provided a revision of the
genus Libys. The gigantic, recently described Megacoelacanthus probably belongs to this family,
based on the characteristics of the pterygoid and
basisphenoid, and not to the Coelacanthidae as
suggested by Schwimmer et al. (1994).
Many authors have considered the actinistians as
an evolutionarily conservative group (see Cloutier,
1991a,b) and Latimeria chalumnae as an example of a
living fossil (Forey, 1984). As early as the Famennian,
the actinistians had acquired their characteristic body
shape. The anterior dorsal fin is located quite anteriorly compared to other sarcopterygians and is never
lobated (Cloutier, 1996a). The anal and posterior dorsal fins are usually strongly lobed and contain endoskeletons and musculature which match those of the
paired fins (Malot and Anthony, 1958) rather than the
median fins of other sarcopterygians. Ahlberg (1992a)
interpreted this pattern as evidence of a type of ho-
meotic transformation, with paired fin structures being expressed at the anal and posterior dorsal fin sites.
Actinistians have a diphycercal caudal fin, symmetrical dorsoventrally and possessing a supplementary
caudal lobe; the only exceptions are Miguashaia, which
has a heterocercal tail (plesiomorphic within the Actinistia), and Allenypterus which has a modified tapering diphycercal tail.
Most of the synapomorphies diagnosing the clade
concern the skull structure, primarily those parts related to the lower jaw and feeding mechanism. Lund
and Lund (1985) and Lund et al. (1985) explained the
conservatism of the jaw apparatus as a response to a
specialized mechanism of suction feeding.
Latimeria is the only living sarcopterygian to possess
an intracranial joint (Lauder, 1980). Through geological time, the ethmosphenoid has become relatively
longer than the otico-occipital part of the neurocranium (Forey, 1991).
ln addition to the mechanoreceptive lateral line system, actinistians have a unique electroreceptive organ
located in the anterior part of the ethmosphenoid, the
rostral organ (Northcutt and Bemis, 1993). In Latimeria, this organ is probably used to localize prey; its use
seems to be linked with a unique headstand behavior
(Fricke et al., 1987).
Among piscine sarcopterygians, the Actinistia is
the only group in which the mode of reproduction
has been documented in the fossil record. Oviparity
has been documented by Schultze (1985) in the Carboniferous Rhabdoderma exiguum. This contrants with
the Recent Latimeria, which is ovoviviparous.
B. Dipnoi
The lungfish clade, Dipnoi, is a universally recognized natural group whose record extends from the
Lower Devonian (Pragian) to Recent (Schultze,
1992a). Approximately 280 species are divided into 64
genera, most represented only by tooth plates (ca. 125
species). The Dipnoi reached their maximum diversity
during the Devonian (more than 85 species) and Triassic (more than 45 species). The 6 living species are
classified into three genera: Protopterus (P. dolloi, P.
annectens, P. aethiopicus, and P. amphibius) from tropical Africa (Greenwood, 1987), Lepidosiren (L. paradoxa)
from South America, and Neoceratodus (N. forsteri)
from Australia (Kemp, 1987). The oldest known members of the group include Uranolophus wyomingensis
Denison 1968a (Beartooth Butte Formation, Wyoming), Diabolepis speratus (Chang and Yu, 1984) (Xitun
Formation, Yunnan, China), and Speonesydrion iani
Campbell and Barwick 1983 (Bloomfield Limestone,
New South Wales, Australia) from the Pragian, and
17. Interrelationships of Basal Sarcopterygians Sorbitorhynchus deleaskitus Wang et al. 1990 (Dale Formation, Guangxi Province, China) and Dipnorhynchus
suessmilchi (Etheridge, 1906) (New South Wales, Australia) from the Emsian. Interrelationships among dipnoans have only partially been assessed and remain
highly debated (Miles, 1977; Marshall, 1987; Campbell
and Barwick, 1990; Schultze et al., 1993; Schultze and
Marshall, 1993; Long, 1993).
The monophyly of the Dipnoi has never been chah
lenged; however, since the discovery of Diabole pis speratus (Chang and Yu, 1984) the definition and diagnosis
of the group have been debated (Maisey, 1986a;
Campbell and Barwick, 1987; Panchen and Smithson,
1987; Schultze, 1987; Schultze and Campbell, 1987;
Cloutier, 1990; Smith and Chang, 1990; Chang,
1991b). The Dipnoi are diagnosed by five uniquely
shared derived characters (Cloutier, 1996b): the absence of marginal teeth on the lower jaw, the presence
of tooth plates on the entopterygoids and prearticulars, a median B-bone located anteriorly or separating
the parietals and postparietals, location of the anterior
margin of the parietals well posterior to the orbits,
and the presence of a labial cavity. Dipnoans are also
characterized by the absence of vomerine fangs, maxilla, extratemporal, fossa autopalatina, and intracranial joint. Most of the characters diagnosing the Dipnoi reflect the peculiar nature of the dentition and
cranial architecture.
Miles (1977) considered Uranolophus wyomingensis
to be the most primitive dipnoan. Campbell and Barwick (1984) regarded Speonesydrion iani and Dipnorhynchus suessmilchi as the most primitive genera but considered these as belonging to another lineage than
Uranolophus. Their arguments were primarily stratigraphical. Schultze and Marshall (1993) used Dipnorhynchus suessmilchi as the functional outgroup for their
phylogenetic analysis of lungfishes. The most controversial species in this respect is Diabolepis spera tus,
which has been considered either as a primitive sarcopterygian related to Powichthys and Porolepiformes
(Panchen and Smithson, 1987), a primitive dipnoan
(Maisey, 1986a; Smith and Chang, 1990), the sistergroup of ail other dipnoans (Cloutier, 1990; Chang,
1991b), the sister-group of the Dipnoi (Chang and Yu,
1984; Ahlberg, 1991b), or a taxon of undetermined
status (Campbell and Barwick, 1987; Schultze and
Campbell, 1987). Campbell and Barwick (1990) ignored Diabolepis in their study on dipnoan phylogeny,
whereas Schultze and Marshall (1993) discussed the
significance of Diabolepis to basal dipnoan relationships without actually including it in the analysis. We
regard Diabolepis as a dipnoan, the sister-group of ahl
other Dipnoi. The clade [Dipnoi excepting Diabolepis]
is supported by four synapomorphies: the palatal p0-
451
sition of both anterior and posterior nares, the absence
of premaxillae (though arguably homoplastic "premaxillae" have been identified in Ganorhynchus, Orlovichthys, and Scaumenacia; R. Cloutier (personal observation), the presence of C-bones, and the passage of
the occipital sensory canal through both extrascapulars and postparietals.
Dipnoan classification is unsettled because there is
no consensus concerning the phylogeny of the group.
Campbell and Barwick (1983, 1987, 1990) divide the
Dipnoi into three lineages on the basis of dentition
(tooth-plated, dentine-plated, and denticulated), but
this phylogeny is unparsimonious (Schultze and Marshall, 1993; Cloutier, 1996b) and has not found general
favor. Schultze's (1993) classification is based on the
strict consensus tree presented by Marshall (1987,
fig. 5).
In order to provide a reasonably manageable taxonomic framework for the bewildering diversity of
the lungfishes, we present here a list of families
combining information from Miles (1977), Campbell
and Barwick (1990), Long (1992), Schultze (1993),
Schultze and Marshall (1993), and Cloutier (1996b).
This should flot be regarded as a definitive statement
of dipnoan taxonomy; several of the families are
certainly or probably nonmonophyletic and require reevaluation.
Diabolepididae Schultze 1993 has only one representative, the Early Devonian Diabolepis speratus,
known exclusively from cranial material (Chang
and Yu, 1984) and isolated dentitional elements
(Smith and Chang, 1990). Its discovery had a crucial impact on our understanding of dipnoan—
porolepiform relationships (Maisey, 1986a; Cloutier, 1990; Ahlberg, 1991b).
Uranolophidae Miles 1977 includes primitive Early
Devonian dipnoans with a denticulated palate.
As in Diabolepis and Dipnorhynchus, the B-bone
separates the parietals but not the postparietals.
Uranolophus wyomingensis is the only species belonging fo this family. It is known from a single
complete specimen and numerous skulls and
lower jaws (Denison, 1968a,b; Campbell and Barwick, 1988).
Dipnorhynchidae Berg 1940 includes Early Devonian, dentine-plated dipnoans with a plesiomorphic skull roof pattern. The group comprises
the genera Dipnorhynchus and Speonesydrion.
Campbell and Barwick (1990) considered Speonesydrion as one of the basal members of their toothplated lineage. Ail species belonging to this family are known from partial skulls and lower jaws
(Campbell and Barwick, 1982b, 1983, 1984). The
452
RICHARD CLOUTIER AND PER ER1K AHLBERG
neurocranium of Dipnorhynchus suessmilchi is the
best known of any Early Devonian lungfish.
Chirodipteridae Campbell and Barwick 1990 is a
Middle to Late Devonian family characterized by
a peculiar type of dentition including dentine tuberosities arranged radially. The members are
Chirodipterus, Pillararhynchus, Gogodipterus, and Palaedaphus. Chirodipterus australis (Gogo Formation,
Lower Frasnian, Australia) is the best known representative (Miles, 1977).
Stomiahykidae Bernacsek 1977 includes Middle to
Late Devonian genera (Stomiahykus and Archaeonectes) with a large tusklike tuberosity at the anterior end of the mesial row of the entopterygoid
tooth plate (Campbell and Barwick, 1990). Long
(1992) considered the Stomiahykidae to be closely
related to the Chirodipteridae.
Dipteridae Owen 1846 is a paraphyletic group of
Middle and Late Devonian forms with tooth
plates, short posterior dorsal fin, and cosmine.
Dipterus valenciennesi (Caithness Flagstone Group,
Eifelian—Givetian, Scotland) is the best understood representative, being known from whole
bodies with well-preserved heads (ForsterCooper, 1937; White, 1965) and parts of the porolepiform-like postcranial endoskeleton (Ahlberg
and Trewin, 1995). More than 20 species referred
to Dipterus are only known from isolated tooth
plates (Schultze, 1992b).
Rhynchodipteridae Berg 1940 includes Middle to
Late Devonian, long-snouted dipnoans with denticulated palates. Rhynchodipterus, Griphognathus,
and Soederberghia belong to this group. The toothplated, long-snouted genus Rhinodipterus is regarded by one of us (RC) as a rhynchodipterid,
but some authors reject this view (Schultze,
1992a). The palatal condition of Iowadipterus remains unknown (Schultze, 1992a). The anatomy
of Griphognathus has been described in detail
(Miles, 1977; Campbell and Barwick, 1988).
Fleurantiidae Berg 1940 includes the latest Givetian
to Famennian dipnoans characterized by the following cranial features (Cloutier, 1996b): (1) rostral part of the skull elongated, (2) wide mouth
gape, (3) single median E-bone, (4) long bone
L 1 +L 2 extending medially to the M-bone, and (5)
elongated entopterygoids bearing large conical
teeth and numerous small denticles, both organized in radiating rows. Cloutier (1996b) discussed the interrelationships among fleurantiids
(i.e., Fleurantia, Jarvikia, Andreyevichthys, and Barwickia). Fleurantia is the best known member of
this family, although informative cranial material
of Andreyevichthys is under study (R. Cloutier,
personal observation).
Phaneropleuridae Huxley 1861 includes Middle to
Late Devonian lungfishes with enlarged bones B,
C, and E, and a general absence of bone D
(Scaumenacia, Phaneropleuron, and Pentlandia). The
length of the posterior dorsal fin is more than
one-quarter of the total length (Cloutier, 1996b).
Schultze and Marshall (1993) considered this family to be paraphyletic. Phaneropleurids are
closely related to fleurantiids.
Uronemidae Traquair 1890 is a monogeneric Carboniferous group, represented by Ganopristodus (=Uronemus), characterized by highly modified tooth
plates with one long lingual tooth ridge and reduced lateral rows (Smith et al., 1987) and a single bone replacing the intertemporal and supratemporal.
Sagenodontidae Romer 1966 is composed of Carboniferous dipnoans with large bone B, reduced parietals and E-bones, and bone L, H-L2 in contact
with bone B (Sagenodus). Tooth plates are formed
by ridges rather than isolated teeth. The anal and
posterior dorsal fins remain separated from the
diphycercal caudal fin (Chorn and Schultze,
1989).
Ctenodontidae Woodward 1891 is composed of Carboniferous dipnoans with a single large bone replacing the intertemporal and bones L, +L 2 (Ctenodus, Tranodis, and Straitonia). The skull roof
pattern of Ctenodus and Tranodis is similar to that
of the uronemids. The position of Straitonia is
questionable because a single element is present
between bones E and B as in Sagenodus.
Conchopomatidae Berg 1940 is a monogeneric
(Conchopoma), Carboniferous to Permian family
characterized by a denticulated parasphenoid
with a rounded anterior margin, concave anterior
margin of bone B, and a single median fin fringe.
Schultze (1975) revised the genus Conchopoma.
Gnathorhizidae Miles 1977 is composed of Late Carboniferous to Early Triassic forms (Palaeophichthys
and Gnathorhiza) in which the otic canal passes in
the postparietal and with numerous cases of dermal bone reduction (large median bone E; single
bone occupying space of bones 3, L, , L 2 , and M;
and single bone in place of intertemporal, supratemporal, and tabular). In the lower jaw, the oral
canal passes in the infradentaries, whereas the
mandibular canal is in an open groove (Schultze
and Marshall, 1993). Gnathorhizids have been
considered as the sister-group of the Lepidosirenidae by Lund (1970) but not by other authors (Ber-
17. Interrelationships of Basal Sarcopterygians man, 1968; Miles, 1977; Schultze and Marshall,
1993).
"Ceratodontidae" Gill 1872 is a paraphyletic group
including Triassic to Tertiary species. The ceratodontid skull roof shows a reduced number of
bones in the median and lateral series. More
than 40 species of Ceratodus have been described,
mostly from tooth plates. Ceratodontids may be
paraphyletic with respect to the neoceratodontids. Schultze (1981) investigated the relationships among so-called ceratodontids (Ptychoceratodus, Microceratodus, Arganodus, Tellerodus, and
Paraceratodus).
Neoceratodontidae Miles 1977 includes Triassic (Epiceratodus) to Recent (Neoceratodus) species with a
reduced postparietal and a single bone occupying
the space of the parietal and bones L1, L2, and
M. Schultze (1981) suggested that Asiatoceratodus
is closely related to Ceratodus owing to the presence in both genera of a single bone replacing
bones A, B, and C.
Lepidosirenidae Bonaparte 1841 is an apomorphic
family including two extant genera (Protopterus
and Lepidosiren) and extinct representatives (e.g.,
the Cretaceous Protopterus regulatus). The skull is
highly derived compared to most dipnoans
(Miles, 1977; Schultze and Marshall, 1993). There
are no cheek bones, nor skull roof bones lateral
to the parietal and postparietal; the vomer is reduced to a patch of small, conical teeth; the nasal
region is kinetic relative to the braincase; and the
jaw adductor muscles attach above the skull roof.
Devonian dipnoan morphology is fairly well documented owing to the material from the Gogo Formation of Australia (e.g., Chirodipterus australis and Griphognathus whitei), Caithness Flagstones of Scotland
(Dipterus valenciennesi), and Escuminac Formation of
Québec (Scaumenacia curta and Fleurantia denticulata).
However, the anatomy of late Paleozoic, Mesozoic,
and Cenozoic species remains poorly understood because most of the species are known only from isolated elements.
The cranial anatomy of dipnoans is better understood than that of the postcranium but has generated
much debate concerning the homology of the dermal
bones. Forster-Cooper (1937) erected a neutral alphanumerical system of nomenclature for the skull roof
(bones A–F, H–J, K–Q, and X–Z) and cheek (bones
T, 1 - 11, and 13-14). Ahlberg (1991b) and Cloutier
(1996b) agreed on the homologies of certain bones
with that of other sarcopterygians: A= median
extrascapular, X= intertemporal, Y1= supratemporal,
453
Y2= tabular, J= parietal, I= postparietal, 1 = lacrimal,
4=postorbital, 8= squamosal, 9=preopercular, and
10= quadratojugal. In Recent forms the skull roof is
greatly reduced compared to Paleozoic species, and
the endocranium is cartilaginous rather than ossified.
Dipnoans display a great deal of intraspecific variation, particularly in the skull roof pattern (Cloutier,
1996b) and probably the greatest amount of diversity
in dermal skull roof pattern among sarcopterygians.
The interpretation of the palatal and cheek bones differs greatly among authors; Rosen et al. (1981) argued
for the presence of a maxilla, premaxilla, and choana
in dipnoans based on their observation on Griphognathus whitei. Branchial and hyoid arches have been described by Miles (1977) for the Frasnian genera Chirodipterus and Griphognathus.
Dipnoans are characterized by peculiar types of
dentition. Most of them lack a marginal dentition;
the maxillae are absent and the premaxillae, when
present, are greatly reduced and bear only a few teeth
(e.g., Scaumenacia, Andreyevichthys, and Ganorhynchus). Paired prearticular and entopterygoid tooth
plates constitute the primary dentitional apparatus of
most species; such tooth plates are known from the
Emsian to the Recent. Two other distinct types of
dentition have been reported: dentine-plated (e.g.,
Dipnorhynchus) and denticulated types (e.g., Uranolophus and Griphognathus). Campbell and Barwick (1983,
1987, 1990) asserted that dipnoans are divided into
two lineages characterized by their dentition—the
tooth-plated and denticulated types. However, this
hypothesis is unparsimonious (Schultze and Marshall, 1993; Cloutier, 1996b) based on the congruence
of cranial and postcranial characters. In contrast to
other gnathostomes, the teeth composing the plates
are flot shed during growth but rather added anteriorly and laterally. This mode of growth allows ontogenetic studies because an adult carnes its own dental
ontogenetic history (Cloutier et al., 1993). Because of
the constant wear on the crushing and/or shearing
surfaces, dipnoans have a hypermineralized tissue
infilling the numerous pulp cavities in the tooth plate,
the petrodentine (Smith, 1984).
Several clearcut patterns, which might justify the
term "trends," can be observed in the history of the
Dipnoi. The earliest representatives of the group
have, with the exception of Diabole pis (Chang and Yu,
1984), already acquired a wholly characteristic "lungfish head" featuring autostyly and a palatal bite. Their
postcranial skeletons however seem hardly to be modified from the generalized sarcopterygian condition
and bear a certain resemblance to those of porolepiforms (Denison, 1968a; Campbell and Barwick, 1988;
454
RICHARD CLOUTIER AND PER ERIK AHLBERG
Ahlberg, 1989, 1991b, 1992b; Ahlberg and Trewin,
1995). During the Middle to Late Devonian, new dipnoan groups (Fleurantiidae, Phaneropleuridae) arise
which have derived postcranial morphologies with
long-based median fins (Ahlberg and Trewin, 1995;
Cloutier, 1996b). All known Carboniferous and later
lungfishes, other than Sagenodus (Chorn and Schultze,
1989), have very derived postcrania with diphycercal
fin fringes rather than separate median fins (Ahlberg
and Trewin, 1995).
In parallel with this morphological change there is
a presumed environmental shift from open marine
environments such as Taemas or Gogo to "Old Red
Sandstone" facies and finally to apparently nonmarine and oxygen-poor environments like coal swamps
(Campbell and Barwick, 1988). Skeletal structures associated with air-breathing (cranial ribs and long parasphenoid stalk) are absent in the primitive marine
lungfishes but appear during the Middle Devonian
and seem to define a clade within the Dipnoi
(Long, 1993).
The dramatic changes in dipnoan median fin morphology during the Paleozoic were used by Dollo
(1895) to infer the evolution of the group (as well as
his principle of the irreversibility of evolution). Paedomorphosis has been suggested as a primary process
in this group in relation to the fusion of the median
fins, reduction of lepidotrichia, reduction of ossification (Bemis, 1984), and dentitional pattern (Cloutier
et al., 1993; Long, 1993). However, in the absence of
a fully resolved phylogeny (Schultze and Marshall,
1993) these hypotheses cannot be fully evaluated
(Ahlberg and Trewin, 1995). Interestingly, the mode
of growth of lungfish tooth plates (see previous discussion) allows the possibility of observing developmental heterochrony in phylogeny. Westoll (1949)
and Schaeffer (1952) compared the evolutionary rates
of dipnoans with the bradytelic evolution of actinistians. However, rates of evolution have never been
calculated in a phylogenetic perspective for the
Dipnoi.
C. Tetrapoda
Although Jarvik (1942, 1972, 1980) and Bjerring
(1989, 1991) continue to argue for tetrapod diphyly
and a urodele—porolepiform relationship, the monophyletic status of the Tetrapoda is supported by a
wealth of characters and is accepted by virtually all
other workers (Schultze, 1970, 1981, 1987; Jurgens,
1973; Gaffney, 1979; Rosen et al., 1981; Shubin and
Alberch, 1986; Panchen and Smithson, 1987; Vorobyeva and Schultze, 1991). It is also supported by molecular evidence (Hedges et al., 1993).
The tetrapods are defined here as a clade characterized by the possession of limbs with digits rather than
paired fins, a pelvis with a sacrum, and zygapophyses; early members can also be recognized by a suite
of derived jaw characters (Ahlberg, 1991a, 1995; Ahlberg et al., 1994). This apomorphy-based definition
encompasses the crown group and part of the stem
group and would thus be seen as unsatisfactory according to the criteria of De Queiroz and Gauthier
(1990). However, at present there is a sharp divide
between early limbed vertebrates such as Ichthyostega
and Acanthostega, whose membership in the tetrapod
stem group can be taken as a well-founded starting
assumption, and tetrapod-like "fishes" such as Panderichthys and Elpistostege, whose membership in the
stem group needs to be tested. We therefore retain
the traditional definition for the present. Note that a
similar situation exists with respect to the Dipnoi.
The tetrapods have a fossil record reaching back
into the Frasnian (Warren and Wakefield, 1972; Ahlberg and Milner, 1994; Ahlberg, 1995). The "traditional" early tetrapod groups, Labyrinthodontia and
Lepospondyli, were exposed as nonnatural during the
past decade (Smithson, 1985; Milner et al., 1986; Panchen and Smithson, 1988). They have not been replaced by a new consensus. However, it is clear that
all the Devonian genera, except perhaps Tulerpeton
(Lebedev and Coates, 1995), fall outside the crown
group. Within the crown group the Amniota and Lissamphibia are Recent sister-groups. The temnospondyls are members of the lissamphibian clade, while
the anthracosaurs probably belong with the amniotes,
but opinions differ as to the position of the loxommatids and the old "lepospondyl" groups (Milner et al.,
1986; Panchen and Smithson, 1988; Trueb and Cloutier, 1991; Carroll, 1992; Ahlberg and Milner, 1994;
Lebedev and Coates, 1995).
The origin of the tetrapod crown group clearly antedates the first appearance of anthracosaurs and temnospondyls in the late Viséan (Ahlberg and Milner,
1994). The tentative assignment of the Russian Famennian tetrapod Tulerpeton to the amniote—anthracosaur
clade (Lebedev and Coates, 1995) suggests an even
earlier date for the split.
In the context of sarcopterygian interrelationships,
the most interesting tetrapods are the Devonian genera. They are not generally placed in higher taxonomie
categories, as their interrelationships are poorly resolved. We recognize eight genera:
Ichthyostega Sâve-Sôderbergh 1932 is represented by
numerous specimens from the Upper Famennian
of eastern Greenland. Most of the skeleton except the manus is known, but the braincase is pe-
17. Interrelationships of Basal Sarcopterygians
culiar and poorly understood (Jarvik, 1980). The
pes has seven digits (Coates and Clack, 1990),
the shoulder lacks a scapular blade (Jarvik, 1980),
lepidotrichia (Jarvik, 1952). Ichand the taul
thyostega is uniquely characterized by the possession of an unpaired median postparietal.
Acanthostega Jarvik 1952 occurs alongside Ichthyostega
in the upper Famennian of eastern Greenland.
Long known only from two incomplete skulls, it
is described in full from new specimens collected
in 1987 (Clack, 1988, 1989, 1994a,b; Coates, 1991;
Coates and Clack, 1990, 1991). Acanthostega's manus has eight digits (Coates and Clack, 1990),
and the same may be truc for the pes (M. I.
Coates, personal communication). The proportions of the forelimb elements are markedly more
fishlike than those of Ichthyostega, and the lepidotrichial tail fin is even larger (Coates, 1995). The
scapulocoracoid is comparable to that of Ichthyostega (Coates and Clack, 1991; M. I. Coates, personal communication).
Tulerpeton Lebedev 1984 is known from a single incomplete body and a number of isolated bones,
all from the upper Famennian Andreyevka-1 locality near Tula, central Russia (Alexeev et al.,
1994). Tulerpeton has a manus with six digits
(Lebedev, 1984). In certain other respects it resembles post-Devonian tetrapods; the limb
bones are slender and a scapular blade is present in the shoulder girdle (Lebedev, 1984; Lebedev and Coates, 1995). Associated bones from
the site, which have not been formally attributed to Tulerpeton, show derived characters like
open lateral line sulci (Lebedev and Clack,
1993) which are not present in the other Devonian tetrapods.
Ventastega Ahlberg et al. 1994 is described from cranial material collected at the upper Famennian
localities of Pavâri and Ketleri in Latvia. Tetrapod
clavicles, interclavicles, and ilia from these localities may also belong to this genus (Ahlberg et al.,
1994). Ventastega is the only upper Famennian
tetrapod known to possess coronoid fangs. In
other respects it broadly resembles Ichthyostega
and Acanthostega.
Hynerpeton Daeschler et al. 1994 is a genus of middle or upper Famennian age, based on a scapulocoracoid+ cleithrum from the Duncannon Member of the Catskill Formation, Pennsylvania. The
shoulder girdle clearly belongs to a stem tetrapod
and resembles that of Ichthyostega as well as the
girdle fragments from Scat Craig.
Metaxygnathus Campbell and Bell 1977 is represented by a single lower jaw ramus from the
455
Cloghnan Shale of New South Wales, Australia,
probably of lower Famennian age (Campbell and
Bell, 1977). The jaw carnes coronoid fangs. The
assignation of Metaxygnathus to the Tetrapoda
has been disputed (Schultze and Arsenault, 1985;
Schultze, 1987). However, its tetrapod nature is
confirmed by a suite of derived characters which
are shared with Acanthostega, Ichthyostega, and
Ventastega but flot with sarcopterygian fishes
(Ahlberg et al., 1994).
Elginer peton Ahlberg 1995 is strictly speaking,
known only from cranial remains, but it has been
associated with postcranial tetrapod bones which
probably also belong to it. This genus cornes
from the upper Frasnian of Scat Craig, Scotland
and is thus together with Obruchevichthys (sec following discussion) the earliest tetrapod known
from skeletal remains. It has several autapomorphies including large size (skull length in excess
of 40 cm; Ahlberg, 1995), triangular head shape
with an acutely pointed snout, and, on the inner
face of the mandible, a broad field of exposed
meckelian bone ventral to the very narrow prearticular. The postcranial tetrapod bones from the
site include an Ichthyostega-like tibia (Ahlberg,
1991a) and robust scapulocoracoids and ilia (Ahlberg, 1995).
Obruchevichthys Vorobyeva 1977 is only known from
two incomplete lower jaws, one from the upper
Frasnian of Latvia and one from an unknown locality in western Russia. It shares several derived
characters with Elginerpeton and appears to be
the sister-group of that genus (Ahlberg, 1995). It
is likely that the Elginerpeton—Obruchevichthys
clade (plesion Elginerpetontidae; Ahlberg, 1995)
is the sister-group of all other Tetrapoda.
Space does not permit us to list the post-Devonian
tetrapod groups.
Apart from the aforementioned genera, the Devonian tetrapod record includes some well-preserved
upper Frasnian trackways from Genoa River, Victoria, Australia (Warren and Wakefield, 1972) and
?Famennian trackways (with more than 150 footprints) from Valentia Island, southwestern Ireland
(Stôssel, 1995). A supposed Lower Devonian trackway from Australia (Warren et al., 1986) cannot be
confidently identified as belonging to a tetrapod,
while the isolated Devonian "tetrapod footprint" described from marine Brazilian deposits by Leonardi
(1983) is probably a starfish trace fossil (Rocek and
Rage, 1994).
Two other genera were described originally as Devonian tetrapods. Elpistostege Westoll 1938 has proved
456
RICHARD CLOUTIER AND PER ERIK AHLBERG
to be a tetrapod-like fish (see following discussion),
while Ichthyostegopsis Sâve-Siiderbergh 1932 appears
to be synonymous with Ichthyostega.
Ichthyostega, Acanthostega, Ventastega, Metaxygnathus, Hynerpeton, Elginerpeton, and Obruchevichthys retain primitive characters not seen in any later tetrapods. Ichthyostega, Acanthostega, and Ventastega share
certain features such as a spade-shaped head, dorsally
placed orbits, external nostril close to the jaw margin,
reduction or loss of the lateral rostral bone, a closed
palate with a mobile basal articulation, and entopterygoids which meet anteriorly in a midiine point between the vomers (Jarvik, 1980; Ahlberg et al., 1994;
Clack, 1994a). The braincases of Acanthostega and Ichthyostega both show a basicranial fissure and some
development of a cranial notochord.
Ichthyostega, Acanthostega, and Tulerpeton possess
more than five digits (Coates and Clack, 1990; Lebedev, 1984). Their humeri, like those of later tetrapods,
are structurally comparable to those of osteolepiforms
and rhizodonts but have a distinctive L shape (Andrews and Westoll, 1970a,b; Rackoff, 1980; Panchen,
1985; Panchen and Smithson, 1987; Ahlberg, 1989). A
late Frasnian humerus from Scat Craig, associated
with Elginerpeton (Ahlberg, 1991a; Ahlberg and Milner, 1994), is morphologically intermediate between
those of Famennian tetrapods and osteolepiforms. Ichthyostega and Acanthostega lack scapular blades but
have well-developed cleithra. Their vertebral columns
are broadly similar to that of Eusthenopteron but have
weakly developed zygapophyses (Andrews and Westoll, 1970a; Jarvik, 1980; Coates, 1995). Both genera
have ribcages; the ribs of Ichthyostega are extremely
broad, overlapping structures (Jarvik, 1980).
D. Onychodontida
The Onychodontida (=Onychodontiformes, Struniiformes) is known only from three genera (Grossius,
Onychodus, and Strunius) ranging from the Pragian
(Zhu and Janvier, 1994) to the Famennian (Schultze,
1993). Zhu and Janvier (1994) described a lower jaw
from the Posongchong Formation of China as the oldest known onychodontid. Grossius is known from a
single three-dimensional skull from the Frasnian of
Spain (Schultze, 1973). Onychodus is represented primarily by parasymphysial tooth spirals and isolated
bones (Jessen, 1966) but also by well-preserved articulated material from the lower Frasnian Gogo Formation of Western Australia (Andrews, 1973; Long,
1991). Jessen (1966) described two species of Strunius
(S. walteri and S. rolandi) from the Frasnian of Germany (Upper Plattenkalk, Bergisch Gladbach) which
at the moment remain the best described members of
the group. Aquesbi (1988) described an onychodontid
from Morocco represented by a single poorly preserved specimen. Material of Onychodus sp. from the
Gogo Formation is being studied by S. M. Andrews
(National Museums of Scotland, Edinburgh). The interrelationships among onychodonts have never been
examined because of the lack of comparative material.
The monophyly of the Onychodontida has never
been addressed in detail. However, the presence of
spiral parasymphysial teeth located dorsal to the dentaries has been suggested as a synapomorphy of the
group (Jessen, 1966; Schultze, 1969, 1973). Aquesbi
(1988) mentioned that the Onychodontida is characterized by the following: (1) a double series of long
sigmoid parasymphysial teeth with striated or crenulated enamel, (2) a large infradentary bordering the
dentary ventrally, (3) the absence of an interdavicle,
and (4) a reduced opercular series. However, the Gogo
Onychodus material contradicts character 2 (P. E. Ahlberg, personal observation). Smith (1989) proposed
the organization of the enamel crystallites of the teeth
into fine ribs with a superficial chevron pattern as an
onychodontid synapomorphy.
The skull combines characters similar to actinopterygians (e.g., well-developed dorsal process on the
maxilla and large preoperculum oriented horizontally)
and typical sarcopterygian features such as an intracranial joint. It seems likely that the "actinopterygianlike" characters are actually plesiomorphic osteichthyan traits.
The sole family, Onychodontidae Woodward 1891,
is coextensive with the Onychodontida.
E. Porolepiformes
The Porolepiformes are an exclusively Devonian
group. The earliest known representatives are several
species of Porolepis from the Pragian (= Siegenian;
Harland et al., 1990) of the Rhineland and Spitsbergen
(Schultze, 1993); the latest is Holoptychius sp. from
the latest Famennian of central Russia (Alexeev et al.,
1994), eastern Greenland (Bendix-Almgreen, 1976),
and elsewhere. Schultze (1993) daims a Tournaisian
record for Holoptychius on the basis of its occurrence
in the Groenlandaspis Series of eastern Greenland.
However, the attribution of this Series to the Carboniferous is questionable. Porolepiforms are absent from
the Tournaisian of central Russia (Alexeev et al., 1994),
North America, and Britain.
Jarvik (1942) was the first worker to recognize that
Porolepis, then the only known member of the family
Porolepididae, shares many characters with Holoptychiidae such as Holoptychius and Glyptolepis. He
united the Porolepididae and Holoptychiidae in the
17. Interrelationships of Basal Sarcopterygians order Porolepiformes Berg (1937). The monophyly of
this group has been accepted by ail subsequent authors
except Maisey (1986a), who interpreted the porolepiforms as a paraphyletic assemblage of stem lungfishes.
However, this interpretation was largely based on the
characteristics of Powichthys and Youngolepis, which fall
outside the Porolepiformes sensu Jarvik (1942).
We define the Porolepiformes as a clade characterized by the possession of dendrodont teeth (Schultze,
1969; Panchen and Smithson, 1987), subsquamosals
(Cloutier, 1990; Ahlberg, 1991b; Cloutier and
Schultze, 1996), and a unique skull roof pattern in
which the intertemporal and supratemporal are absent and the postotic sensory canal passes through
the growth center of the postparietal bone (Ahlberg,
1992c). The clade thus defined is equivalent to Porolepiformes of Jarvik (1942), although the diagnostic
characters are different.
The porolepiforms are not a diverse group. We
recognize eight genera, two in the Porolepididae and
six in the Holoptychiidae:
"Porolepididae" Berg 1940 is a paraphyletic group
defined by the possession of cosmine. The best
known genus is Porolepis Woodward 1891, which
ranges in age from Pragian to Givetian (Schultze,
1993). It is unclear whether Porolepis is a clade or
simply a paraphyletic assemblage of primitive
porolepiforms. Heimenia Orvig 1969, also has cosmine, but the scale morphology is intermediate
between those of Porolepis and the Holoptychiidae (Orvig, 1969). Only scales and a single lower
jaw of Heimenia (Jarvik, 1972, pl. 12-6) have been
figured or described to date.
Holoptychiidae Owen 1860 is a clade defined by the
possession of round scales, lack of cosmine, lack
of median gular plate, and a relatively short ethmosphenoid cranial division (Ahlberg, 1992c).
Glyptolepis Miller ex Agassiz 1841, ranges from
the Eifelian to the early Frasnian (Lyarskaya,
1981). As traditionally defined, this genus may
be paraphyletic with respect to other holoptychiids (Ahlberg, 1992c). Quebecius Schultze 1973,
from the middle Frasnian of Miguasha, Québec
(Cloutier et al., 1996), resembles Glyptolepis but is
distinguished by a unique cheekplate pattern
(Cloutier and Schultze, 1996). The early Frasnian
genus Laccognathus Cross 1941, is defined by an
autapomorphic dermal ornament composed of
large tubercles with thick enamel (Orvig, 1957)
and by the possession of very large infradentary
foramina (Cross, 1941; Ahlberg, 1992c). Holoptychius Agassiz in Murchison 1839, ranges in time
from the middle Frasnian (Jarvik, 1972; Cloutier
457
et al., 1996) fo the end of the Devonian (Alexeev
et al., 1994; see previous discussion). It has dermal ornament composed of laminar bone rather
than dentine (Orvig, 1957). Duffichthys Ahlberg
1992c, is represented by autapomorphic lower
jaws from the upper Frasnian of Scat Craig, Scotland. The Middle Devonian genus Hamodus Obruchev 1933 is only known from isolated, very
large dendrodont teeth with barbed tips. A further holoptychiid genus, Paraglyptolepis Vorobyeva 1987, has been described from the Givetian
of Estonia. However, on basis of the available material it is flot clear that this genus can be distinguished from Glyptolepis.
In the Early and Middle Devonian, porolepiforms
tend to be the largest predators in the faunas where
they occur (Ahlberg, 1992b). Maximum size for the
group seems to be close to 2m. They seem to have
been the first sarcopterygian group to evolve elaborate
branched lateral fine systems; their cranial sensory
canals have numerous first- and second-order side
branches, which cover almost the whole skull surface
except the operculogular series. The gross morphology of the holoptychiids is extremely stereotyped
(Ahlberg, 1992b).
On the whole, porolepiform cranial anatomy is
fairly similar to that of osteolepiforms. This is particularly true for the intracranial joint, which runs through
the profundus foramen in both groups. However, the
ethmosphenoid braincase block and lower jaw are
much doser to those of Powichthys and Youngolepis
(Jessen, 1980; Chang, 1982, 1991a; Ahlberg, 1991b).
The basibranchial skeleton lacks a sublingual rod, unlike that of osteolepiforms (Jarvik, 1972). The vertebral
column is lungfish-like, as are the archipterygial pectoral fins (Ahlberg, 1989, 1991b). However, the pelvic
fins have asymmetrical endoskeletons of a more generalized sarcopterygian pattern (Ahlberg, 1989). The
spread of anatomical information among the Porolepiformes is patchy. The postcranial endoskeleton has
only been described from Glyptole pis, although personal observation (by P.E. Ahlberg) of Laccognathus
specimens in the care of Emilia Vorobyeva shows a
very similar vertebral column and fin supports.
F. Powichthys and Youngolepis
These two genera from the Early Devonian (Lochkovian—Pragian) of Arctic Canada (Powichthys) and
South China and Vietnam (Youngolepis) show affinities
with both porolepiforms and lungfishes. They are
known mostly from cranial remains, although the
shoulder girdle of Youngolepis was described by Chang
458
RICHARD CLOUTIER AND PER ERIK AHLBERG
(1991a) and a cleithrum associated with Powichthys
was figured by Jessen (1980).
Powichthys Jessen 1975, from Prince of Wales Island
in the Canadian Arctic, is the more porolepiform-like
of the two and was referred to the Porolepiformes by
its discoverer (Jessen, 1975, 1980). However, it lacks
the derived porolepiform skull roof pattern and has
polyplocodont rather than dendrodont tooth folding.
Powichthys resembles the porolepiforms most closely
in the structure of its ethmosphenoid. It has a pair of
well-developed internasal pits between the vomers,
and there is a large profundus foramen in the postnasal wall. However, the snout also contains rostral tubuli like those in lungfishes (Jessen, 1980). An opercular series associated with the genus (but not formally
attributed to it; Jessen, 1980) appears to have contained a preoperculosubmandibular bone similar to
that of porolepiforms. The lower jaw (again not formally attributed, but very probably belonging to
Powichthys) has a porolepiform-like parasymphysial
tooth plate attachment and three infradentary foramina similar to those of Holoptychius and Laccognathus.
However, the immobilized intracranial joint lies at the
level of the trigeminal and lateral ophthalmic nerves,
as in coelacanths.
Youngolepis Chang 1982, from Yunnan, China
(Chang, 1982, 1991b) and Vietnam (Tong-Dzuy Thanh
and Janvier, 1990, 1994), has an extraordinary braincase which combines porolepiform- and lungfish-like
features with apparent actinopterygian characteristics. The latter are most obvious around the posterior
part of the braincase floor. There is a basicranial fissure
rather than a fenestra. A "basicranial process" from
the lateral commissure reaches forward toward a
"processus descendens" from the sphenoid (Chang,
1982) just as in Mitnia (Gardiner, 1984). The sphenoid
is pierced by separate foramina for the carotid and
efferent pseudobranchial arteries. Although these features are otherwise known only from actinopterygian s, they are probably to be interpreted as plesiomorphic osteichthyan characters (Ahlberg, 1994). In
Youngolepis their co-occurrence with an unconstricted
cranial notochord, and an apparent remnant of the
intracranial joint in the side wall of the braincase
(Chang, 1982), raises the possibility that they are reversals from a fully developed intracranial joint.
Other parts of the anatomy of Youngolepis seem to
show a mixture of porolepiform, lungfish, and general sarcopterygian characters. The lower jaw resembles that associated with Powichthys and has infradentary foramina, the snout contains rostral tubuli
as in Powichthys and lungfishes, the cheekplate is
broadly osteolepiform-Iike with extensive squamosal-
maxillary contact, and the shoulder girdle has a flattened but essentially tripodal scapulocoracoid.
G. Osteolepiformes
The Osteolepiformes (Berg, 1937; Jarvik, 1942) is
by far the most diverse of the extinct sarcopterygian
groups though much less diverse than the Actinistia,
Dipnoi, or Tetrapoda. Approximately 60 species from
some 25 genera have been described, ranging in age
from Middle Devonian (Eifelian) to Lower Permian
(Sakmarian). Among them is Eusthenopteron foordi, the
most thoroughly studied fossil sarcopterygian and
one of the best known of all fossil vertebrates (Whiteaves, 1883, 1889; Goodrich, 1902; Jarvik, 1937, 1942,
1944a,b, 1954, 1963, 1980; Andrews and Westoll,
1970a). Yet for all this our anatomical knowledge of the
osteolepiforms remains patchy; Eusthenopteron stands
out against a host of incomplete and poorly understood genera.
The overall impression given by the osteolepiforms
is of a rather homogenous group of similar-looking
fishes. However, this homogeneity does not necessarily imply monophyly; it is possible that the group
Osteolepiformes is paraphyletic relative to the Rhizodontida, Elpistostegalia + Tetrapoda, or both.
The cranial anatomy is best illustrated by Eusthenopteron, although comparable information on the neurocranium is available from Megalichthys (Romer,
1937), Gogonasus (Long, 1988a), and Medoevia (Lebedev, 1995). The dermal skull bones are well known
in the Scottish Middle Devonian genera Osteolepis,
Thursius, and Gyroptychius (Jarvik, 1948). The braincase
is divided by an intracranial joint running through the
foramen for the profundus nerve. There is only one external nostril on each side of the head, buta large palatal
opening surrounded by vomer, dermopalatine, maxilla, and premaxilla appears to have transmitted a
choana (Jarvik, 1942; Panchen and Smithson, 1987).
This interpretation was challenged by Rosen et al.
(1981), who tried to show that the size of the opening
had been exaggerated by Jarvik. However, new evidence from acid-prepared specimens (Long, 1988a;
Lebedev, 1995; P. E. Ahlberg, personal observation)
corroborates Jarvik's description and shows that the
opening bears a very close resemblance to the choanae
of Devonian tetrapods (Jarvik, 1980; Clack, 1994a). The
otoccipital braincase block broadly resembles that of actinistians but retains lateral otic fissures which end in
large vestibular fontanelles.
Dermal bone characteristics of the group include a
large squamosal which separates the rather narrow
preopercular from the maxilla. Cosmine is primitively
459
17. Interrelationships of Basal Sarcopterygians
present in osteolepiforms but has been lost in many
genera. Vertebrae are either rhachitomous or ringcentra (Andrews and Westoll, 1970a,b). Ribs, if present, are short. The paired fin skeletons are short, uniserial metapterygia, and ail fin radiais are unjointed
and unbranched (Andrews and Westoll, 1970a,b). The
humerus is structurally very similar to that of basal
tetrapods, although the actual shape is rather different
(Ahlberg, 1991a,b). In the majority of osteolepiforms
the paired and median fin bases carry enlarged scales,
the so-called basal scutes.
The classification of the Osteolepiformes is in urgent need of revision. Schultze (1993) divides them
into the following families:
"Osteolepididae" Cope 1889 is a paraphyletic group
of primitive osteolepiforms. A typical representative is Thursius Sedgwick and Murchison 1828.
Within this group, the megalichthyids can be recognized as a clade on the basis of several cranial
characters (Young et al., 1992). The osteolepidids
range in time from Devonian (Eifelian) to Permian (Sakmarian).
Canowindridae Young et al. 1992 is a clade characterized by a posteriorly broad postparietal shield,
lateral extrascapulars which almost meet in the
midline anteriorly, and exclusion of the postorbital from the orbital margin. Three canowindrid
genera are known: Canowindra Thomson 1973,
Beelarongia Long 1987, and Koharale pis Young et
al. 1992. At present the group appears restricted
to the Upper Devonian of Australia and Antarctica.
Tristichopteridae Cope 1889 (=Eusthenopteridae
Berg 1940) is a clade characterized by the presence of posttemporal bones between the operculars and lateral extrascapulars. Tristichopterids
also lack cosmine, have thin round scales with a
median ridge on the inner surface, and possess a
characteristic triphycercal caudal fin. The earliest
known tristichopterid is Tristichopterus (Andrews
and Westoll, 1970b) from the upper Givetian
John O'Groats Sandstone, Scotland, while the latest is Eus thenodon from the upper Famennian
Remigolepis Series of eastern Greenland (Jarvik,
1952). Marsdenichthys from the Frasnian of Australia is held by Long (1985) to be the most primitive known member of the group. Eusthenopteron
is the only tristichopterid to have been studied in
great detail, and relationships within the group
remain obscure.
Rhizodopsidae Berg 1940 is a group ranging from
the Carboniferous to Permian. The best known
genus is Rhizodopsis (Andrews and Westoll,
1970b; Moy-Thomas and Miles, 1971).
H. Rhizodontida
The Rhizodontida (Andrews and Westoll, 1970b)
are a group of Devonian and Carboniferous fishes
chiefly remarkable for their great size. The Scottish
Lower Carboniferous form Rhizodus hibberti seems to
have reached a length of 7 m (Andrews, 1985). Most
known rhizodont specimens consist of partly or
wholly disarticulated material. Only one complete individual, a juvenile of ?Strepsodus anculonamensis, has
been described; it has an elongate body with small
median fins clustered near the diamond-shaped
symmetrical tai (Andrews, 1985, fig. 2; this paper,
Fig. 2g).
Despite our incomplete knowledge of rhizodont
anatomy, the Rhizodontida can unambiguously be
recognized as a clade. Synapomorphies of the group
include robust lepidotrichia with extremely long unjointed proximal portions, and the presence on the
cleithrum of a depressed posterior flange and an elaborate double overlap area for the clavicle (Andrews
and Westoll, 1970b; Andrews, 1985; Long, 1989;
Young et al., 1992). The humerus has a bulbous head
which forms a bail-and-socket joint with the round
glenoid, and the radiais of the pectoral fin skeleton
are both jointed and branched (Andrews and Westoll,
1970b). Cosmine is always absent and the scales are
round and thin.
The best understood part of rhizodont anatomy is
the pectoral girdle. Parts of the dermal skull have
been described from ?Strepsodus and from Screbinodus
(Andrews, 1985) and Barameda (Long, 1989). The bone
pattern is broadly similar to that of osteolepiforms,
but Barameda (the most complete rhizodont) shows
some unusual characters such as an extratemporal
which contacts the supratemporal ("intertemporal" of
Long, 1989) and a reduced postrostral mosaic. Long
(1989) interpreted Barameda as having two external
nostrils on each side. However, the reconstructed pattern conflicts with evidence from a detached Strepsodus premaxilla (BMNH P364(2); P. E. Ahlberg, personal observation) which shows a continuous overlap
area for the lateral rostral in the region where Long
placed the anterior nostril. Andrews (1985) reconstructed an osteolepiform-like arrangement of bones
in the narial region but felt uncertain whether one or
two nostrils were present. It is also unclear whether
rhizodonts possess a choana. The condition of the
nasal region is important, as the supposed possession
of two external nostrils was one of the main features
460
RICHARD CLOUTIER AND PER ERIK AHLBERG
which led Long (1989), Ahlberg (1991b), and Young
et al. (1992) to place rhizodonts below osteolepiforms
in the tetrapod stem group.
A number of braincase fragments have been described from the Antarctic genus Notorhizodon (Young
et al., 1992). They include a well-developed intracranial joint and closely resemble the corresponding parts
of Eusthenopteron; this also applies to the palatoquadrate of Notorhizodon (Young et al., 1992). The lower
jaw, known from Notorhizodon and in part also from
Barameda (Long, 1989) and Strepsodus (Andrews,
1985), resembles those of osteolepiforms and porolepiforms. It has a very strongly developed symphysial
fang pair on the dentary.
Probably the earliest known rhizodont is Notorhizodon from the "Middle—Late Devonian" Aztec Siltstone
of Antarctica (Young et al., 1992), while the last known
representative is Strepsodus from the Westphalian Coal
Measures of England (Schultze, 1993). The only analysis undertaken to date of rhizodont interrelationships
was that of Young et al. (1992), which produced the
following topology: [Notorhizodon + [Barameda +
[Screbinodus + [Rhizodus + Strepsodus]]]]. This hypothesis is biogeographically interesting in that the two
genera judged to be most primitive both derive from
East Gondwana.
I. Elpistostegalia
This group is generally known as Panderichthyida
Vorobyeva 1989, but Elpistostegalia Camp and Allison
1961 has priority (Schultze, 1996). The name of the
single constituent family should likewise be Elpistostegidae Romer 1947, rather than Panderichthyidae
Vorobyeva and Lyarskaya 1968. The group is of great
phylogenetic interest because its members display a
melange of tetrapod-like and osteolepiform-like characters. It is stratigraphically restricted and of low diversity; at present we recognize only two genera and
three species.
Elpistostege Westoll 1938 is represented by the single
species Elpistostege watsoni from the middle Frasnian of Miguasha, Québec, Canada. Two incomplete skulls and a section of vertebral column are
known (Schultze and Arsenault, 1985) of this
youngest elpistostegid.
Panderichthys rhombolepis Gross 1941 was originally
described on the basis of incomplete lower jaws
from the early Fra snian of Latvia. The discovery
of several complete specimens at Lode quarry in
Latvia (Lyarskaya and Mark-Kurik, 1972) resulted
in a series of descriptive and interpretive papers
(Vorobyeva, 1977, 1980, 1986, 1989; Vorobyeva
and Tsessarskii, 1986; Vorobyeva and Schultze,
1991; Vorobyeva and Kuznetsov, 1992; Worobjewa, 1975) which have made this the best
known elpistostegid.
Panderichthys stolbovi Vorobyeva 1960 is a slightly
younger, though still early Frasnian, species
from Russia that is known from a snout fragment
and some incomplete lower jaws (Vorobyeva,
1960, 1962, 1971). Panderichthys stolbovi appears
very similar to P. rhombolepis, but the two can be
distinguished by their slightly different dermal ornament (P. E. Ahlberg, personal observation).
In addition to these bona fide elpistostegids, Panderichthys bystrovi Gross 1941 and Obruchevichthys gracilis Vorobyeva 1977 have also been attributed to the
group. The material of "Panderichthys" bystrovi cornes
from the late Famennian locality of Ketleri in Latvia.
The holotype, a mandibular fragment, needs to be
redescribed; it certainly cornes from a sarcopterygian
fish but does not appear to belong to an elpistostegid
(P. E. Ahlberg, personal observation). The maxilla and
premaxilla attributed to P. bystrovi by Vorobyeva
(1962) actually belong to a tetrapod, Ventastega curonica
(Ahlberg et al., 1994). Obruchevichthys, which is known
only from two late Frasnian mandibular fragments,
also appears to be a primitive tetrapod (Ahlberg,
1991a, 1995; Ahlberg et al., 1994; see below). Genuine
elpistostegids are thus at present restricted to the early
and middle Frasnian.
Elpistostegid cranial anatomy resembles that of osteolepiforms in many respects. In Panderichthys rhombolepis and P. stolbovi (the two species where this region is known) the anterior end of the palate compares
with that in Eusthenopteron: the vomers have welldeveloped posterior processes which suture to the
sides of the parasphenoid and prevent the entopterygoids from meeting in the midline. This is quite different from the tetrapod pattern. The lower jaw likewise
lacks obvious tetrapod characteristics (Ahlberg, 1991a)
but resembles those of tristichopterids such as Eusthenodon (P. E. Ahlberg, personal observation) and
Platycephalichthys (Vorobyeva, 1962) as well as that of
the rhizodont Notorhizodon (Young et al., 1992). The
bone and sensory line pattern around the external
nostril matches that of Eusthenopteron (Vorobyeva and
Schultze, 1991; Jarvik, 1980).
The most obvious tetrapod-like structure in the elpistostegid skull is a pair of frontals anterior to the
parietals (Westoll, 1938; Vorobyeva, 1977; Schultze
and Arsenault, 1985; Vorobyeva and Schultze, 1991).
It is worth noting in passing that the elpistostegid
skull roof pattern furnishes powerful support for Westoll's (1938) terminology of dermal skull bones in osteichthyan fishes (Schultze and Arsenault, 1985;
17. Interrelationships of Basal Sarcopterygians
Ahlberg, 1991b). As in tetrapods, but unlike osteolepiforms, the parietals and postparietals of elpistostegids
are immovably sutured together. The intracranial joint
must thus have been immobile and was possibly obliterated altogether.
Just as striking as these anatomical structures is the
tetrapod-like morphology of the elpistostegid head.
The skull is flattened and spade-shaped, the orbits
are dorsal and crowned by bony "eyebrows," the interorbital skull roof is narrow and concave, and the
external nostrils are almost marginal. These features
must be related to the mode of life of the animais,
and may indicate a shallow-water or marginal lifestyle
(Ahlberg and Milner, 1994; Schultze, 1996).
A similar situation obtains with respect to the postcranial skeleton; the straight tau, lack of separate dorsal and anal fins, and probably dorsoventrally flattened body of Panderichthys rhombolepis can ail be
matched in Ichthyostega and Acanthostega and suggest
that the elpistostegids may have had a capacity for
terrestrial locomotion (Vorobyeva and Kuznetsov,
1992). The humerus and scapulocoracoid of P. rhombole pis combine tetrapod-like features with apparent autapomorphies (Vorobyeva and Schultze, 1991; Vorobyeva and Kuznetsov, 1992). Unfortunately these
elements are unknown in the other two species. The
vertebral column of P. rhombolepis has peculiar bladelike ribs which are sutured to the intercentra and neural arches. Pleurocentra are absent (Vorobyeva and
Tsessarskii, 1986). Similar bladelike elements in a vertebral column attributed to Elpistostege are identified
as neural arches by Schultze and Arsenault (1985),
but these too appear to be ribs (R. Cloutier, personal observation).
The combination of characters seen in the Elpistostegalia raises important phylogenetic questions. Their
synapomorphies with tetrapods are striking and suggest that the two are sister-groups (Vorobyeva and
Schultze, 1991; Cloutier, 1990; Ahlberg, 1991b; Ahlberg and Milner, 1994; but see Panchen and Smithson,
1987). Many of their plesiomorphic characters are
general osteichthyan traits and thus unproblematical,
but others are shared specifically with tristichopterids
and rhizodonts and could pose a challenge to osteolepiform monophyly (see preceeding sections). Most
interesting of ail are the characters that bear on the
question of elpistostegid monophyly. Vorobyeva and
Schultze (1991) propose five elpistostegid synapomorphies: (1) median rostral separated from premaxilla,
(2) paired posterior postrostrals, (3) large median gular, (4) lateral recess in nasal capsule, and (5) subterminal mouth (= prominent snout). Character lis erroneous, as a comparable median rostral is developed in
both osteolepiforms and basal tetrapods (Jarvik, 1980;
461
Ahlberg, 1995). Characters 2, 3, and 4 are ail indeterminable in tetrapods (the postrostral mosaic and gular
series have been lost altogether, while the nasal capsules are unossified and thus unknown in ail fossil
tetrapods) and thus not really testable. This seems
to leave a prominent snout as the only elpistostegid
synapomorphy.
Set against this character are a couple of features
(intertemporal present in Panderichthys rhombolepis but
absent in Elpistostege and known Devonian tetrapods;
more tetrapod-like ornament in Elpistostege than in
P. rhombolepis, P. E. Ahlberg, personal observation)
which suggest the Elpistostegalia might be paraphyletic with respect to the tetrapods. At present our
understanding of Elpistostege and P. stolbovi is too incomplete to allow the question of elpistostegid monophyly or paraphyly to be settled. However, the
implications of the question are profound: if the elpistostegids are paraphyletic with respect to tetrapods,
the many morphological details which give a common
elpistostegid appearance to Elpistostege and P. rhombolepis (snout outline, shape and position of "eyebrows," etc.) will actually be attributes of the tetrapod
stem lineage. A paraphyletic group Elpistostegalia
would, in other words, provide much more detailed
information about the earliest stages of tetrapod evolution than would an elpistostegid clade. The investigation of this area should be a priority for future sarcopterygian research programs.
III. The Character Set
The character set which we present is essentially a
consensus list based on our earlier works (Ahlberg,
1989, 1991b; Cloutier, 1990), with the addition of a
few characters from other sources (e.g., Chang and
Smith, 1992). A total of 140 characters were combined
(Appendix 1), and these include only those characters
that can be recognized in early fossil sarcopterygians.
The reasons for this approach are worth examining.
The debate over the relative merits of fossil and recent data goes back two decades (Lovtrup, 1977; Patterson and Rosen, 1977; Patterson, 1981, 1982a,b; Rosen
et al., 1981; Schoch, 1986; Doyle and Donoghue, 1986,
1987; Donoghue et al., 1989; Forey, 1987; Panchen and
Smithson, 1987; Schultze, 1987, 1994; Campbell and
Barwick, 1987, 1988; Gauthier et al., 1988; Huelsenbeck,
1991). It has often been clouded by conflation with the
separate issue of whether fossils can be taken to represent actual ancestors of Recent forms. However, the
view that fossil and recent organisms should ail be
treated as terminal taxa in a phylogenetic analysis has
gradually gained near-universal acceptartce.
462
RICHARD CLOUTIER AND PER ERIK AHLBERG
There are two main schools of thought about the
treatment of fossil data in a cladistic analysis. One
argues that the cladogram should be constructed on
the basis of character distributions among the living
taxa and that fossils should only then be mapped
onto the topology; the fossils are thus not allowed to
modify the topology. This approach was applied by
Patterson and Rosen (1977) to teleosts, and by Forey
(1987)—with certain reservations—to sarcopterygians. The other school rejects this division and uses
both fossil and Recent data in the initial analysis. Most
paleontologists appear to fall into the latter school
(Schultze, 1987; Panchen and Smithson, 1987; Vorobyeva and Schultze, 1991; Chang, 1991a,b).
We follow Gauthier et al. (1988) in rejecting a priori
primacy for the characters of Recent taxa. In some
cases, the character combinations displayed by sequences of plesions manifestly have the capacity to
overturn phylogenetic judgements based on living
taxa alone, and we can see no justification for artificially preventing this outcome.
White it is generally possible to get better and more
de tailed anatomical information from Recent taxa than
from fossils, this is not equally true for all characters.
Features of adult skeletal morphology are often just as
well understood in well-preserved fossils as in Recent
organisms. The real disadvantage of fossils lies in the
complete absence of certain kinds of data such as
physiology, development, and in most cases soft anatorny and gene sequences. We designate these as
"neontological" characters and use the term "paleontological" for such characters as can be detected in
both living and fossil organisms.
In practice, all character sets are affected by at least
one of three types of problems which limit their usefulness in phylogenetic analysis. These are the following:
Incomplete distribution: the characters are not
known in all of the relevant taxa owing to anatomical
incompleteness of the organisms.
Poor understanding or definition of characters: the
characters have limited "information content," making it difficult to distinguish homology from homoplasy.
(3) Low number of characters: the character set is too
small to provide adequate support for all nodes.
Purely neontological data sets are usually not much
affected by problem 3 but will suffer from 1 in direct
proportion to the number of fossil taxa involved in
the phylogenetic analysis. Paleontological data sets
are often prone to problems 2 and 3. They are also
affected by 1, in so far as fossil taxa are often incomplete. However, whereas "neontological" characters
are typically known in all living taxa and unknown
in all fossil ones, the gaps in a paleontological data
set are determined by the preservation of different
fossils and are likely to be more randomly distributed
across the range of taxa.
The Sarcopterygii includes three crown groups,
namely the Tetrapoda (amniotes + lissamphibians),
the Dipnoi (Neoceratodus, Protopterus, and Lepidosiren),
and the Actinistia (Latimeria). The tetrapod and dipnoan crown groups date back approximately to the
basal Carboniferous and the Lower Triassic, respectively (Ahlberg and Milner, 1994; Schultze and Marshall, 1993), whereas the monospecific actinistian
crown group has no fossil record at all. However, each
of these crown groups is associated with a recognized
stem group which reaches back to the Devonian; there
is no disagreement that Acanthostega and Ichthyostega
are stem tetrapods, Dipnorhynchus and Uranolophus are
stem dipnoans, and Diplocercides and Euporosteus are
stem actinistians. Alongside the long-lived clades we
find exclusively Paleozoic groups such as onychodonts, osteolepiforms, elpistostegids, porolepiforms,
and rhizodonts. Some of these appear to be clades,
but others may be paraphyletic taxa (Rosen et al., 1981;
Young et al., 1992). We also have the more isolated
Early Devonian genera Powichthys, Youngolepis, and
Kenichthys (Jessen, 1975, 1980; Chang, 1982, 1991a,b;
Chang and Smith, 1992; Chang and Zhu, 1993).
The main phylogenetic uncertainties revolve
around the relationships between the long-lived clades
and various extinct groups; all the most debated phylogenetic nodes lie in or below the Devonian. Furthermore, outgroup-based phylogenetic analyses of the
long-lived clades (Cloutier, 1991a,b; Forey, 1991;
Schultze et al., 1993; Ahlberg and Milner, 1994; Lebedev and Coates, 1995) indicate that the most plesiomorphic and phylogenetically basal members of each
clade are Devonian fossil genera. Fossil taxa thus occupy crucial positions in the analysis, and it is clear
that paleontological characters will be very important
for sorting out their relationships. However, we have
decided to go one step further in omitting neontological data from the analysis altogether.
The overall neontological data set divides naturally
into morphological information and molecular data.
Molecular phylogenetics is a relatively new field, but
a number of workers have already tackled the threetaxon problem of lungfishes, actinistians and tetrapods (Meyer and Wilson, 1990, 1991; Gorr et al., 1991;
Stock et al., 1991; Stock and Swofford, 1991; Sharp et
al., 1991; Normark et al., 1991; Hedges et al., 1993).
No consensus view has yet emerged from this research, and there are significant methodological disagreements within the field, although the bulk of the
17. Interrelat onships of Basal Sarcopterygians molecular evidence seems to support a lungfishtetrapod sister-group relationship (Meyer, 1995). As
a detailed discussion of the role of molecular data is
given by Marshall and Schultze (1992) and Schultze
(1994), we will flot give any further consideration to
molecular data in this paper.
In recent years the most important investigations
of neontological anatomy have been those of Fritzsch
(1987, 1988, 1992), Trueb and Cloutier (1991), and
Northcutt and Bemis (1993). Fritzsch described some
possible coelacanth-tetrapod synapomorphies from
the structure of the inner ear, as did Northcutt and
Bemis (1993) who focused on neurological characters;
Trueb and Cloutier favored the topology [Actinistia + [Dipnoi + Tetrapodaff Our main reason for flot
using these data is a wish to focus attention on the
flood of new paleontological information which has
become available during the past two decades (see
Historical Background). A subsidiary consideration is
the distribution of the data. Because neontological
characters are unknown in ail the fossil taxa and can
only support a few of the many nodes in the phylogenetic reconstruction, the use of large numbers of such
characters seems likely to affect the analysis in unpredictable ways.
Under the circumstances, we prefer to focus our
present analysis entirely on the paleontological data
set (Appendix 2). In effect, we want to see whether
the "basal radiation" of sarcopterygians—i.e., the
short-lived groups and the early representatives of
the surviving clades—contains any obvious phylogenetic pattern. The results can then be compared
with neontological (both molecular and morphological) and "total evidence" phylogenies for the Sarcopterygii in order to map out areas of agreement
and disagreement.
IV. Discussion
The data matrix includes 140 characters and a total
of 158 apomorphic character-states (Appendix 3). Appendix 1 provides the complete list of characters and
their respective character-states. All characters were
entered unordered and unweighted. All but one taxon
(the actinopterygian Polypterus) are extinct ranging in
lime from the Lower Devonian to the Upper Carboniferous (Appendix 2). Most of the data matrix (Appendix 3) was coded based on our respective observation
of original material with the exception of Howqualepis
(Long, 1988b), Speonesydrion (Campbell and Barwick,
1983, 1984), Dipnorhynchus (Campbell and Barwick,
1982a,b), Beelarongia (Long, 1987; Young et al., 1992),
and Barameda (Long, 1989).
463
Fifty-four most parsimonious trees at 277 steps
were found using the heuristic search (C.I. = 0.578;
C.I. excluding uninformative characters = 0.572;
R.I. = 0.818) using the 140 characters coded for 32 taxa
(including five outgroup taxa). The tree was rooted on
a monophyletic outgroup including Polypterus, Cheirolepis, Mhnia, Moythornasia, and Hourqualepis. The Adams and strict consensus trees show the same topology (Fig. 3). Four topological variants were found: (1)
among dipnoans, (2) at the base of the Tetrapodomorpha, (3) among osteolepiforms, and (4) among tetrapods. As the characters selected for the analysis were
chosen for their potential to resolve relationships between (rather than within) acknowledged clades, the
topological variation at variants (1) and (4) can be
disregarded as unimportant.
The monophyly of the Actinistia, Onychodontida,
Dipnoiformes, Porolepiformes, Rhizodontida, Elpistostegalia, and Tetrapoda is corroborated (Table 1).
However, the Osteolepiformes and Youngolepidida
do flot appear to be monophyletic groups. The monophyly of most clades is robust (72% for the Elpistostegalia and Rhizodontida to 98% for the Actinistia and Dipnoi, based on 100 bootstrap replicates); a monophyletic
Osteolepiformes has been replicated only 34%.
The Actinistia is the sister-group of the remaining
sarcopterygians (i.e [Onychodontida + Rhipidisfiai). Two clades constitute the Rhipidistia: (1) the
Dipnomorpha including the Dipnoiformes and Porolepiformes and (2) the Tetrapodomorpha. In contrast
to the conclusions of Chang and Smith (1992), Powichthys and Youngolepis do flot form a monophyletic
group but rather consecutive plesions in the stem
group of the Dipnoi; this pattern had been postulated
by Ahlberg (1991b). Thus we consider the Dipnoiformes to include Powichthys, Youngolepis, and Dipnoi.
There is no evidence for the monophyly of the
Youngolepididae (Gardiner, 1984), Youngolepiformes
(Chang and Smith, 1992), and Youngolepidida
(Young et al., 1992). The dipnoan Diabolepis is considered to be the sister-group of the remaining Dipnoi
as suggested by Cloutier (1990) and Chang (1991b).
The Rhizodontida is the sister-group of the Osteolepidida as suggested by numerous authors (Cloutier,
1990; Ahlberg, 1991b; Vorobyeva and Schultze, 1991;
Young et al., 1992). The interrelationships within the
Osteolepidida are as follow: rOsteolepiformes" + [Elpistostegalia + Tetrapodall. As first suggested by
Schultze and Arsenault (1985), the Elpistostegalia is the
sister-group of the Tetrapoda. However, in terms of
extant organisms, the Dipnoi is the Recent sister-group
of the Tetrapoda as suggested by Rosen et al. (1981).
The distribution of characters is given for the major
nodes concerning interrelationships among sarco-
RICHARD CLOUTIER AND PER ERIK AHLBERG
464
CC.:c
0sk.Ch
.\
e
CC
C).\'› ‘Ç.'
.
) \e
›o
s
,,,
° &
,4'
,e c
Q,
, c,
:-.'
Q' t '. '.. '0 0c.,'t, e>‹,
» e ..
.e rt
.(1..
e'D'('''
Q9.'bre'e
.. se CD n,. q:‘,>
''.'
0
...!
e,
•
\
()
c, ‘ços 0pn,'•oO ,§`
, •••
0 . \ • c,O.\
C') b
e
e: ) ••••
Ack. g". c... 0 e 0 ?:,,,,00•r• \t,,CD 0(>,..
e n,
‘ (‘ q> k c,
• \ c k',:k.'C'l"-et, o z g. .5,
''.7)
cc
Jk,t, ccc2.
,.' • rb,‘0cc 'C<2,,,Q2 c P.,c9 c) ,0 e <zz•.,c, c,g nz '..:‘ sc,, r.5 C, n,..n`)`(‘ eur''q . re..
(C . ..,
n ' ,)'' ,('',0)(:),a\
0Z
c, qy
c,
>
.e,,,
, ,.,,,
.2)•b 0 :b
q
\
.
,
J
'o
..)
Q
. 0 ,..,'..,\ c„).. e , 'ç, ç„ (,,d<,,,,.(z,'' '.çs , .g,<>,0c,' c.,\z.
•:.-
o ck ,, c; « z ,e ‘D çî. ,,; „cs, ..ç. Q.,
c., .,,:cr,
,...o
.
c,..
cc
(t)
„.,,,e.;,,,,,
'ZY \c.) 0 .z;
,‘' c., o. c'),
ô N°
'"`\'\ . ..Ç'c,
° e .., ce,,
.°)'`;s7'
0,O,.c0‘<tr. (`),0.. 00e; 0o 0-\
O, •O 0o'.,-0, o 0 •'es*
c) c
05,0o c0 0 0, ° `‘..,,.O et,‘'z',4°b
, o 2
,p.,s§\c)
'\.
\. N ''' 0. 0, -\
\
,.,/,
,t, 0. Q . 0 (t \ è;"e, -\<•., ,o'z' j"
c
)r''
'`°)\-C.)‘‘'CZ('
' \- ecM,` °e`'.-1,0cc,,c
c;" o o ,a (<, <;(t c) e e- 4,
j
L
FIGURE 3 Interrelationships of 28 sarcopterygian taxa. Adams and strict consensus tree
based on the 54 most parsimonious trees at 277 steps [C.I. = 0.578; R.I. = 0.818].
A. Sarcopterygii Romer 1955
pterygian higher taxa (Fig. 4). Complete lists of character changes for these nodes are given in Table 1. Only
the uniquely shared, derived characters common to
the 54 most parsimonious trees are discussed in this
section unless controversial anatomical structures
are involved.
TABLE 1
Taxa
Sarcopterygii
[Onychodontida + Rhipidistia]
Rhipidistia
Dipnomorpha
Dipnoiformes
[Youngolepis + Dipnoi]
Tetrapodomorpha
Osteolepidida
[Elpistostegalia + Tetrapoda]
Actinistia
Onychodontida
Porolepiformes
Dipnoi
Rhizodontida
Elpistostegalia
Tetrapoda
Although unquestioned, the monophyly of the Sarcopterygii was supported by more than 30 characters
(Table 1). Some of the synapomorphies represent the
presence of new structures [tectals (char. 42), the
Distribution of Characters Common to the 54 Most Parsimonious Trees for
Major Sarcopterygian Clades
Uniquely shared derived characters
4, 18, 42, 49, 52, 54, 63(2), 88, 93(1),
105-106, 110, 120, 128
93(2)
56
2, 41, 43, 130
10, 77, 100, 119(1)
17, 45, 108
44, 71, 119(2), 122
15, 38, 67, 127
76, 95, 97, 138
41(2)
14(2), 51, 55, 63, 75, 101
30, 65, 80
114, 132(2)
33
24, 39, 60-61, 68, 125
Reversais
62, 66, 118
34, 74, 121, 135, 137
48, 81, 86, 89-90, 139
59, 82-84, 102
32, 79, 92
113, 124
81-84, 139
Homoplasies
3, 28, 29(2), 34, 37, 40(2), 74, 81-85,
89, 94, 96, 112-113, 121, 124, 137
12, 35, 48, 64, 79, 92, 103, 139
14, 21, 29, 115-116
1, 31(1), 59, 78, 123
87
29, 73
12, 14, 35, 79, 85, 92, 111
70
20, 25, 47, 58, 135(2)
19, 53, 58, 87, 91, 117, 129
11, 36, 57(2)
20, 36, 37(2), 129
9, 19, 31(2), 47, 58, 91
64
62, 66, 112(2)
Note. The category "uniquely shared derived characters" lists ail characters with a C.I. equal to 1. The names of Taxa are those used in
the text and in Fig. 4. See trees in Figs. 3 and 4. Appendix 1 provides the character descriptions.
17. Interrelationships of Basal Sarcopterygians
l>'r
Zr
0
,e e
,...
0
n‘.
/
CD
-..',
e ,
* n '
.'"
e
' n''
,,- ,. .
e
,,,
e .9 &
d e ,z()e,r)
«e e 4.-- e
(Y
. •''
,.,?
e
e
Ô'
DI PNOIFORM ES
OSTEOLEPID IDA
TETRAPODOMORPHA
D IPNOM OR PHA
RHI PI DISTIA
SARCOPTERYGII
Interrelationships of sarcopterygian higher taxa. The
topology corresponds to the phylogenetic tree illustrated in Fig. 3.
See Table 1 and text for the distribution of characters.
FIGURE 4
squamosal (char. 54), the splenial (char. 93(1)), the
jugal canal (char. 106), the humerus (char. 120), and
basal plates in the dorsal fin supports (char. 128)]. In
addition, structural and topographical changes occurred in the skull in comparison to basal actinopterygians: the premaxilla do flot form part of the orbit (char.
18), more than four sclerotic plates compose the sclerotic ring (char. 49), the dermohyal is absent (char.
52), the hyomandibular has two proximal articular
heads instead of one (char. 88), the preopercular canal
does not end at the dorsal margin of the preopercular
(char. 105), and the mandibular canal does not pass
through the dentary (char. 110).
Characters 18, 52, 105, 106, 110, and 128 are complementary to the synapomorphies already identified for
the Sarcopterygii (see Forey, 1980; Rosen et al., 1981;
Gardiner, 1984; Maisey, 1986a; Panchen and Smithson, 1987; Schultze, 1987; Cloutier, 1990; Ahlberg,
1991b). The presence of cosmine (char. 1) and submandibulars (char. 64; Gardiner, 1984; Schultze, 1987)
are flot sarcopterygian synapomorphies because actinistians lack these structures. Numerous branchial
and hyoid characters used by previous authors (Forey,
1980; Maisey, 1986a; Panchen and Smithson, 1987)
were not included in our analysis owing to the lack
of information in the taxa analyzed.
B. [Onychodontida + Rhipidistia]
Of the nine characters supporting this clade, only
one is not subsequently transformed. In addition to
the splenial and angular, the infradentary series includes the postsplenial and surangular [char. 93(2)1.
Based on this topology, the absence of surangular in
actinistians (Cloutier, 1991a,b, 1996a) cannot be considered a synapomorphy of the group.
Of special interest at this node is the presence of
character 48—palatal opening ("choana") surrounded
465
by the premaxilla, maxilla, dermopalatine, and vomer. The condition is known in Eusthenopteron, Panderichthys, tetrapods, and holoptychiids (P. E. Ahlberg, personal observation); the palatal opening is
absent in dipnoans. Because the condition is unknown in onychodontids, it is possible that this character supports only the Rhipidistia. Nevertheless, the
distribution of this character is contradictorv to that
hypothesized by various authors (Panchen and Smithson, 1987; Schultze, 1987, 1991). The interpretation of
a palatal opening in porolepiforms agrees with the
identification of a fenestra endochoanalis in Glyptole pis
by Jarvik (1972) and Bjerring (1991). Thus, if one accepts this interpretation as suggested by the distribution of the characters, it follows that the posterior
external nostril and the choana are nonhomologous
since onychodonts and porolepiforms have two external nares. Schultze (1987, 1991) and Chang (1991b)
argued that porolepiforms lack a true choana because
the palatal part of the fenestra ventrolateralis is covered by the vomer (and possibly the dermopalatines).
However, Section 62 of Jarvik's grinding series of
Glyptolepis groenlandica (Jarvik, 1972: fig. 8C) shows
on both sides of the snout a palatal opening which
communicates unambiguously with the posterior external nostril and the nasal cavity. Furthermore, a
specimen of Holoptychius from Dura Den (Scotland)
prepared by one of us (P. E. Ahlberg) shows a small
round opening at the junction of the maxilla, premaxilla, dermopalatine, and vomer, which seems to correspond precisely with the choana reconstructed by Jarvik (1972) and Bjerring (1991) from the grinding series
of Glyptolepis. This opening is similar in size to the
external nostrils. Although this topic could benefit
from further study, the currently available evidence
thus supports Jarvik's and Bjerring's interpretation.
C. Rhipidistia Cope 1871
Nine transformations corroborate the monophyly
of the Rhipidistia (Table 1), of which only one is
uniquely derived. In rhipidistians, the preopercular
does not contact the maxilla (char. 56) because of a
suture between the squamosal (or subsquamosals in
porolepiforms) and the quadratojugal; in dipnoans in
which the maxilla is absent, the preopercular does not
reach the ventral margin of the cheek.
In his overview of sarcopterygian tooth structure,
Schultze (1970) identified three types of dentine folding (plicidentine) in order (1) to characterize certain
sarcopterygian clades, (2) to suggest a close relationship between Osteolepiformes and Tetrapoda, and
(3) to demonstrate the monophyly of the Tetrapoda.
Among the three types, polyplocodont plicidentine
466
RICHARD CLOUTIER AND PER ERIK AHLBERG
was said to be plesiomorphic, but no transformation
series were inferred. Based on our tree, one has to
consider that the dendrodont (in Porolepiformes) and
eusthenodont types of folding (Schultze, 1970)
evolved from a polyplocodont pattern. Thus the polyplocodont folding is not a synapomorphy of the clade
[Rhizodontida + Osteolepidida] as suggested by Long
(1989) and Young et al. (1992).
D. Dipnomorpha Ahlberg 1991b
The Dipnoi is closely related to the Porolepiformes
(Maisey, 1986a; Ahlberg, 1989, 1991b; Cloutier, 1990,
1991a; Chang, 1991a,b; Chang and Smith, 1992) and
not the sister-group of remaining sarcopterygians
(Fig. ld; Schultze 1987, 1994) nor that of the Tetrapoda (Fig. lb; Rosen et al., 1981; Gardiner, 1984). In
our analysis, the clade [Dipnoiformes + Porolepiformes] is supported by the following four characters:
mesh canais of the cosmine pore-canal system without
horizontal partition (char. 2), median extrascapular
overlapping the lateral extrascapulars [char. 41(1)1,
three or more tectals (char. 43), and presence of posterior branched radial complex associated with the
posterior dorsal fin (char. 130).
Ahlberg (1991b) was the first to propose a large
suite of characters (17) to support the monophyly of
the clade [Porolepiformes + [Powichthys + [Youngolepis + [Diabolepis + Dipnoi]]]] (Fig. le). Of the characters used by Ahlberg (1991b), only 9 were included
in our analysis (our characters 31, 34, 59, 71, 79, 100,
123, 130, and 137); some were combined (e.g., char.
137) or simply deleted owing to the lack of morphological information. Only character 130 is fully congruent
with Ahlberg's hypothesis. Because our analysis was
performed at a lower taxonomie level, some of the
characters considered as uniquely shared derived are
homoplastic with respect to various taxa (e.g., character 123 is also present in the rhizodontid Bararneda).
The absence of a contact between the supraorbital
and the parietal (char. 34) was considered by Ahlberg
(1991b) as a dipnomorph uniquely shared derived
character. Recent studies of the basal actinopterygian
Cheirolepis canadensis by Arratia and Cloutier (1996)
show that a supraorbital is present in this species and
that there is no contact between it and the parietal.
Thus the polarity of the character is different than that
of Ahlberg (1991b) as well as its distribution.
The presence of preoperculosubmandibulars (char.
59) is frequently considered as a porolepiform synapomorphy (Jarvik, 1972; Vorobyeva and Schultze, 1991;
Cloutier, 1990). Based on this analysis and Ahlberg
(1991b), it is reinterpreted as a dipnomorph synapomorphy. It is likely that some of the 9-bones of dip-
noans are homologous to the preoperculosubmandibular found in porolepiforms and Powichthys.
E. Dipnoiformes Cloutier 1990
The Dipnoiformes is defined as the clade [Powichthys + [Youngolepis + Dipnoi]]. Powichthys and Youngolepis are consecutive plesions in the stem group of the
Dipnoi; this pattern had been postulated by Ahlberg
(1991b). The distribution of characters could be subject
to further changes because ail the basal taxa of this
clade (Powichthys, Youngolepis, Diabolepis, Dipnorhynchus, and Speonesydrion) are only known from incomplete specimens (mainly partial skulls). Characters 10,
77, 100, and 119 are congruently distributed; there are
an additional seven characters.
Chang and Smith (1992) and Chang and Zhu (1993)
considered a broad marginal "tooth field" on the coronoids (char. 10) as a character shared by Youngolepis
and Powichthys (also present in Kenichthys). Coronoids
are absent in dipnoans.
The presence of rostral tubuli is shared by Powichthys, Youngolepis, and basal dipnoans (char. 77). The
infraorbital canal follows the dorsal margin of the premaxilla (char. 100); this condition might be related to
the condition of character 17 at the following node.
The proximal articular surface of the humerus is
flat [char. 119(1)] rather than concave (plesiomorphic
condition) or convex (Tetrapodomorpha synapomorphy). However, the distribution of character 119 could
be an artifact of the selection of the taxa and the availability of information. Among basal dipnoiforms, the
condition is only inferred in Youngolepis based on the
condition of the glenoid fossa (Chang, 1991a). However, in advanced dipnoans the articular surface is
concave (Schultze, 1987; Ahlberg, 1989).
Within the Dipnoiformes, the clade [Youngolepis +
Dipnoi] is supported by characters 17, 45, and 108 and
five reversais (Table 1). The position of the premaxilla
(char. 17) in Youngolepis is interpreted as a transitional
state between a plesiomorphic condition in which it
forms the anterior part of the upper maxillary arcade
and the derived dipnoan condition where the premaxilla is absent or reduced to a small dentigenous part.
The posterior naris is still external but located very
close to the jaw margin [char. 45(1)]; this condition
precedes the dipnoan one in which the posterior naris
occupies a palatal position. On the lower jaw, the
middle pit line developed into an enclosed oral canal
or a structure of intermediate morphology (char. 108).
F. Tetrapodomorpha Ahlberg 1991b
The Tetrapodomorpha includes the Rhizodontida,
Elpistostegalia, Tetrapoda, and the so-called osteo-
17. Interrelationships of Basal Sarcopterygians
lepiforms. Significant modifications involve the anatomy of the nasal region and anterior palate as well as
the pectoral appendage. The Tetrapodomorpha
shares a single external flans which corresponds to
the anterior naris (char 44); howeyer, the condition is
unknown in the Rhizodontida. The vomers articulate
with each other medially (char. 71), and paired intervomerine pits are absent [char. 79(0)1. The anatomy
of the humerus is modified: its proximal articular surface is convex [char. 119(2)1 and the deltoid and supinator processes are present (char. 122).
Vorobyeva and Schultze (1991) refer to this clade
as the Choanata; the main differences between their
interpretation of the clade and ours concern the position of the Osteolepiformes and the distribution of
some characters. They listed 21 characters of which
10 were used in our analysis (our characters 22-23,
41, 44, 48, 63, 66, 70, 119, and 140). The distribution
of characters 44 and 119 are congruent in both hypotheses; however, Young et al. (1992) considered that the
Rhizodontida lacks character 44.
The presence of a palatal opening surrounded by
the maxilla, premaxilla, vomer, and dermopalatine
(char. 48) is interpreted in our analysis as a synapomorphy of the Rhipidistia because of its presence in
holoptychiids. The median extrascapular is overlapped by the lateral extrascapulars (char. 41) flot only
in members of this clade but also in actinistians. This
relationship among the extrascapulars is considered
to be plesiomorphic for the Sarcopterygii and is flot
diagnostic for the Tetrapodomorpha as suggested by
Jarvik (1980), Vorobyeva and Schultze (1991), and
Young et al. (1992).
Vorobyeva and Schultze (1991) define a character
as "median gular always present" which they consider to be a synapomorphy of this clade; in our analysis, the presence of a median gular (char. 66) characterizes the rhipidistian node (and a large actinopterygian
clade) and changes in holoptychiids and tetrapods.
The polarity of character 66 is ambiguous because
most basal actinopterygians possess a median gular
with the exception of Polypterus. Based on our topology, the presence of a median gular is homoplastic
with respect to actinopterygians and rhipidistians.
Vorobyeva and Schultze (1991) also mention the presence of the posterior process on the vomer as a synapomorphy of this clade, although they note that the
character is absent in some osteolepiforms. This character (char. 70) is in fact absent in the rhizodont Barameda (Long, 1989) as well as in the osteolepiform
Medoevia (Lebedev, 1995) and Gogonasus (Long,
1988a), and the condition is unknown in Strepsodus
and many osteolepiforms. The process is known to
be present in tristichopterids, elpistostegids, and Crassigyrinus.
467
Other characters listed by Vorobyeva and Schultze
(1991), flot used in our analysis, deserve some comments. A separate median rostral is present in osteolepiforms, elpistostegids, and basal tetrapods (Jarvik,
1980; Ahlberg, 1995); thus a median rostral fused with
the premaxilla is not a synapomorphy of this clade.
A "long parasphenoid extending below oticooccipital
region" is in fact restricted to crown-group Tetrapoda.
The presence of seyen submandibulars is also found
in porolepiforms (Cloutier and Schultze, 1996).
G. Osteolepidida Boulenger 1901
The Osteolepidida are defined herein as the clade
rOsteolepiformes" + [Elpistostegalia + Tetrapoda]].
This "traditional" osteolepiform—tetrapod relationship is defined in terms of shared derived characters
and congruence of characters (Schultze, 1987; Panchen and Smithson, 1987; Long, 1989; Cloutier, 1990,
1991b; Ahlberg, 1991b; Vorobyeva and Schultze, 1991;
Young et al., 1992; Ahlberg and Milner, 1994). This
node is corroborated by character 70 and two reversals
(chars. 113 and 124). The vomer has a distinctive posterior process (char. 70) which is lost in some basal
tetrapods. (As mentioned above, this character is arguably primitively absent in some osteolepiforms and
may thus in fact define a somewhat less inclusive
clade.) The anocleithrum is exposed externally [char.
113(0)1; this character is considered as a reversai, although the plesiomorphic condition in actinopterygians deals with the postcleithrum. The mesomeres of
the pectoral fin lack postaxial radiais [char. 124(0)1 in
contrast to porolepiforms, dipnoans, and rhizodonts.
In contrast to the hypotheses of Janvier (1980), Long
(1985), and Vorobyeva and Schultze (1991), the monophyly of the Osteolepiformes is flot corroborated by
our analysis; however, the paraphyly of the group
is not demonstrated either. The monophyly of the
osteolepiforms is jeopardized by the relative position
of Eusthenopteron. Three equally parsimonious topologies have been obtained: Eusthenopteron is either the
sister-group of (1) [Osteolepididae + Canowindridae], (2) [Elpistostegalia + Tetrapoda], or (3) [remaining osteolepiforms + [Elpistostegalia + Tetrapodall
In topologies 2 and 3, the Osteolepiformes is paraphyletic, whereas in topology 1 the monophyly is demonstrated. In topology 1, the presence of a large median
postrostral (char. 23) and basal scutes on the fins (char.
131) would be considered as osteolepiform synapomorphies. A close relationship with the clade [Elpistostegalia + Tetrapoda] is optimized by character 140
(presence of well-ossified ribs) and the reversai of
character 35 (absence of extratemporal). In terms of
anatomy, the third topology is less robust because the
clade [[Osteolepididae + Canowindridae] + [Elpisto-
468
RICHARD CLOUTIER AND PER ERIK AHLBERG
stegalia + Tetrapoda]] is supported by the reversai of
two highly homoplastic characters: the presence of
rhombic scales (char. 3) and the bilateral halves of the
neural arch are separated (char. 136).
H. [Elpistostegalia + Tetrapoda]
The relationship between the Elpistostegalia and
the Tetrapoda is well-corroborated. As mentioned
by Schultze and Arsenault (1985) and Vorobyeva and
Schultze (1991), the shape of the skull (char. 15) and
the composition of the median series of skull roofing
bones (char. 25) are diagnostic of this clade; the orbits
are located dorsally, the interorbital distance is narrow
and concave, and the skull as a whole is flattened.
Paired frontals are present anterior to the parietals
(char. 25); the superficially similar condition observed
in Polypterus spp. is homoplastic with respect to this
clade and these elements are not homologous to the
frontals. The spiracle is present as a large, posteriorly
open notch (char. 38) in the posterior part of the skull
table enclosed between the tabular and the cheek
bones. The unpaired fins (dorsal and anal fins) are lost
(char. 127). The shape of the caudal fin is modified, the
epichordal lepidotrichia being more developed than
the hypochordal ones [char. 135(2)].
V. Conclusions
The Sarcopterygii represents a well-diagnosed
clade composed of seven unambiguous subclades
(i.e., Actinistia, Onychodontida, Dipnoiformes, Porolepiformes, Rhizodontida, Elpistostegalia, and Tetrapoda) and one questionable taxon (i.e., Osteolepiformes). A cladistic analysis of 140 osteological
characters yielded the following phylogenetic conclusions (congruence with published analyses indicated
by references):
The Actinistia is the sister-group of the remaining sarcopterygians (i.e., [Onychodontida + Rhipidistia]) (Panchen and Smithson, 1987).
The Onychodontida is the sister-group to the
Rhipidistia.
The Dipnomorpha (including the Dipnoiformes
and Porolepiformes) is the sister-group of the Tetrapodomorpha (Maisey, 1986a; Cloutier, 1990; Ahlberg, 1991b).
The Dipnoiformes (including Powichthys, Youngolepis, and Dipnoi) is the sister-group of the Porolepiformes (Maisey, 1986a; Cloutier, 1990, 1991a; Ahlberg,
1991b; Chang, 1991b; Chang and Smith, 1992).
The Rhizodontida is the sister-group of the Osteolepidida (Long, 1989; Cloutier, 1990; Ahlberg,
1991b; Vorobyeva and Schultze, 1991; Young et al.,
1992).
The interrelationships within the Osteolepidida
are as follow: ["Osteolepiformes" + [Elpistostegalia
+ Tetrapoda]] (Schultze, 1987, 1991, 1994; Cloutier,
1990, 1991a; Ahlberg, 1991b; Young et al., 1992).
The Elpistostegalia is the sister-group of the Tetrapoda (Schultze and Arsenault, 1985; Schultze, 1987,
1991, 1994; Cloutier, 1990; Ahlberg, 1991b; Vorobyeva
and Schultze, 1991).
In terms of extant organisms, the Dipnoi is the
Recent sister-group of the Tetrapoda (Forey, 1980,
1987; Gardiner, 1980, 1984; Rosen et al., 1981; Maisey,
1986a; Cloutier, 1990, 1991a; Ahlberg, 1991b; Forey et
al., 1991; Trueb and Cloutier, 1991).
The classification proposed in this paper requires
a reinterpretation of the diagnosis (characters) and
definition (taxa) of already existing taxonomic categories. Available taxonomic names have been used and
reassigned to clades that agree the closest to their
original definition. We are not assigning Linnean rank
to the taxonomic categories. Instead indentation signifies relative hierarchical rank. The classification of the
Sarcopterygii based on this cladistic analysis is summarized as follows:
Sarcopterygii Romer 1955
Actinistia Cope 1871
[Onychodontida + Rhipidistia] clade
Onychodontidat Andrews 1973
Rhipidistia Cope 1887
Dipnomorpha Ahlberg 1991b
Porolepiformes' Jarvik 1942
Dipnoiformes Cloutier 1990
Tetrapodomorpha Ahlberg 1991b
Rhizodontida t Andrews and Westoll 1970b
Osteolepidida Boulenger 1901
"Osteolepiformes t" Berg 1937
[Elpistostegalia + Tetrapoda] clade
Elpistostegaliat Camp and Allison 1961
Tetrapoda Haworth 1825
VI. Summary
Sarcopterygians are classified into three extant
groups (i.e., Actinistia, Dipnoiformes, and Tetrapoda)
and five extinct Paleozoic taxa (i.e., Onychodontida,
Porolepiformes, Rhizodontida, Osteolepiformes, and
Elpistostegalia); sarcopterygian fishes (excluding tetrapods) account for approximately 500 species belonging to approximately 160 genera. The diagnosis, taxo-
17. Interrelat onships of Basal Sarcopterygians nomic content, stratigraphic range, evolutionary
trends, and classification of the eight sarcopterygian
higher clades are described. Fifty-four most parsimonious trees were found using 140 osteological characters (referred to as "the paleontological characters")
coded for 27 sarcopterygian basal taxa. The character
distribution is discussed for the most parsimonious
sarcopterygian topology: [Actinistia + Forolepiformes + Dipnoiformes1 + [Rhizodontida + ["osteolepiforms" + [ Elpistostegalia + Tetrapoda111111. The
controversial Devonian genera Youngolepis and Pounchthys are included in the Dipnoiformes; the Dipnoiformes together with the Porolepiformes constitute
the Dipnomorpha which is the sister-group of the
Tetrapodomorpha. Although osteolepiforms are
closely related to the clade [Elpistostegalia + Tetrapoda], their monophyly is flot corroborated. The Elpistostegalia is the sister-group of the Tetrapoda,
whereas dipnoans are the living sister-group to the
tetrapods.
Acknowledgments
It is a pleasure to have this opportunity to acknowledge Colin
Patterson's great contributions to vertebrate paleontology and systematics. He has played a major part-through his own work and
through his influence on others-in placing the study of sarcopterygian interrelationships on a rigorous cladistic basis and thus shaping
the field in which we work. On a personal level, we have both had
the pleasure of working in the rigorous intellectual climate which
he has encouraged and maintained at the Natural History Museum,
London, and we owe him more pints of beer than we can readily
remember. Thank you, Colin.
This paper draws on some 10 years' worth of accumulated work,
and there are many people who have helped and influenced us in
various ways during that time. We thank, in no particular order,
Hans-Peter Schultze, Jenny Clack, Peter Forey, Brian Gardiner,
Michael Coates, Erik Jarvik, Philippe Janvier, Mahala Andrews,
Chang Mee-Mann, Gloria Arratia, Oleg Lebedev, John Long and
Marius Arsenault, as well as many others whom we cannot list here.
Referen ces
Ahlberg, P. E. (1989). Paired fin skeletons and relationships of the
fossil group Porolepiformes (Osteichthyes: Sarcopterygii). Zool.
J. Linn. Soc. 96, 119-166.
Ahlberg, P. E. (1991a). Tetrapod or near-tetrapod remains for the
Upper Devonian of Scotland. Nature (London) 354, 298-301.
Ahlberg, P. E. (1991b). A re-examination of sarcopterygian interrelationships, with special reference to the Porolepiformes. Zool. J.
Lion. Soc. 103, 241-287.
Ahlberg, P. E. (1992a). Coelacanth fins and evolution. Nature (London) 358, 459.
Ahlberg, P. E. (1992b). The palaeoecology and evolutionary history
of the porolepiform sarcopterygians. In "Fossil Fishes as Living
Animais" (E. Mark-Kurik, ed.), pp. 71-90. Academy of Sciences
of Estonia, Tallinn.
Ahlberg, P. E. (1992c). A new holoptychiid porolepiform fish from
the Upper Frasnian of Elgin, Scotland. Palaeontology 35, 813-828.
469
Ahlberg, P. E. (1994). The intracranial joint in vertebrate phylogeny.
J. Morphol. 220 (ICVM-4 Abstr.), 319.
Ahlberg, P. E. (1995). Elginerpeton pancheni and the earliest tetrapod
clade. Nature (London) 373, 420-425.
Ahlberg, P. E., and Milner, A. R. (1994). The origin and early
diversification of tetrapods. Nature (London) 368, 507-514.
Ahlberg, P. E., and Trewin, N. H. (1995). The postcranial skeleton
of the Middle Devonian lungfish Dipterus valenciennesi. Trans.
R. Soc. Edinburgh: Earth Sci. 85, 159-175.
Ahlberg, P. E., Luksevics, E., and Lebedev, 0. (1994). The first
tetrapod finds from the Devonian (Upper Famennian) of Latvia.
Philos. Trans. R. Soc. London, Ser. B 343, 303-328.
Alexeev, A. A., Lebedev, O. A., Barskov, I. S., Barskova, M. I.,
Kononova, L. I., and Chizova, V. A. (1994). On the stratigraphic
position of the Famennian and Tournaisian fossil vertebrate
beds in Andreyevka, Tula Region, Central Russia. Proc. Geol.
Assoc. 105, 41-52.
Andrews, S. M. (1973). Interrelationships of crossopterygians. In
"Interrelationships of Fishes", (P. H. Greenwood, R. S. Miles,
and C. Patterson, eds.), pp. 137-177. Academic Press, London.
Andrews, S. M. (1985). Rhizodont crossopterygian fish from the
Dinantian of Foulden, Berwickshire, Scotland, with a re-evaluation of this group. Trans. R. Soc. Edinburgh: Earth Sci. 76, 6795.
Andrews, S. M., and Westoll, T. S. (1970a). The postcranial skeleton
of Eusthenopteron foordi Whiteaves. Trans. R. Soc. Edinburgh
68(9), 207-329.
Andrews, S. M., and Westoll, T. S. (1970b). The postcranial skeleton
of rhipidistian fishes excluding Eusthenopteron. Trans. R. Soc.
Edinburgh 68(12), 391-489.
Aquesbi, N. (1988). Étude d'un Onychodontiforme (Osteichthyes,
Sarcopterygii) du Dévonien moyen (Eifelien) du Maroc. Bull.
Mus. Na!!. Hist. Na!. [4] 10, 181-196.
Arratia, G., and Cloutier, R., (1996). Reassessment of the morphology of Cheirolepis canadensis (Actinopterygii). In "Devonian
Fishes and Plants from Miguasha, Quebec, Canada" (H.-P.
Schultze and R. Cloutier, eds.), pp. 165-197. Verlag Dr. Fredrich
Pfeil, Munich.
Bemis, W. E. (1984). Paedomorphosis and the evolution of the
Dipnoi. Paleobiology 10, 293-307.
Bendix-Almgreen, S. E. (1976). Palaeovertebrate faunas of Greenland. In "Geology of Greenland" (A. Escher and W. S. Watt,
eds.), pp. 536-573. Geol. Surv. Greenland, Copenhagen.
Berg, L. S. (1937). A classification of fish-like vertebrates. Bull. Acad.
Sci. URSS, pp. 1277-1280.
Berg, L. S. (1940). Classification of fishes, both recent and fossil.
Tr. Zool, lus!., Akad. Nauk SSSR 5, 1-517.
Berg, L. S. (1955). Classification of fish-like vertebrates, living and
fossil. 2., corrected and enlarg. Tr. Zool, lus!., Akad. Nauk SSSR
20, 1-286.
Berg, L. S. (1958). "System der rezenten und fossilen fischartigen
und Fische." Deutcher Verlag der Wissenschaften. VEB, Berlin
(translation by W. Gross of Berg, 1955).
Berman, D. S (1968). Lungfish from the Lueders Formation (Lower
Permian, Texas) and the Gnathorhiza-lepidosirenid ancestry
questioned. J. Paleontol. 42, 827-835.
Bernacsek, G. M. (1977). A lungfish cranium from the Middle Devonian of the Yukon Territory, Canada. Palaeontographica, Abt.
A 157, 175-200.
Bjerring, H. C. (1989). Apertures of craniate olfactory organs. Acta
Zool. (Stockholm) 70, 71-85.
Bjerring, H. C. (1991). Some features of the olfactory organ in the
Middle Devonian porolepiform Glyptolepis groenlandica. Palaeontographica, Abt. A 219, 89-95.
Bjerring, H. C. (1993). Yet another interpretation of the coelacanthi-
470
RICHARD CLOUTIER AND PER ERIK AHLBERG
form basicranial muscle and its innervation. Acta Zool. (Stockholm) 74, 289-299.
Camp, C. L., and Allison, H. J. (1961). Bibliography of fossil vertebrates 1949-1953. Mem. Geol. Soc. Am. 84, 1-53.
Campbell, K. S. W., and Barwick, R. E. (1982a). A new species of
the lungfish Dipnorhynchus from New South Wales. Palaeontology
25, 509-527.
Campbell, K. S. W., and Barwick, R. E. (1982b). The neurocranium
of the primitive dipnoan Dipnorhynchus sussmilchi (Etheridge).
J. Vertebr. Paleontol. 2, 286 - 327.
Campbell, K. S. W., and Barwick, R. E. (1983). Early evolution of
dipnoan dentitions and a new genus Speonesydrion. Mem. Assoc.
Australas. Palaeontol. 1, 17 - 49.
Campbell, K. S. W., and Barwick, R. E. (1984). Speonesydrion, an
Early Devonian dipnoan with primitive toothplates. Palaeo 'chthyologica 2, 1 - 48.
Campbell, K. S. W., and Barwick, R. E. (1987). Paleozoic lungfishes-a review. J. Morphol., Suppl. 1, 93-131.
Campbell, K. S. W., and Barwick, R. E. (1988). Uranolophus: A
reappraisal of a primitive dipnoan. Mem. Assoc. Australas. Palaeontol. 7, 87-144.
Campbell, K. S. W., and Barwick, R. E. (1990). Paleozoic dipnoan
phylogeny: Functional complexes and evolution without parsimony. Paleobiology 16, 143-169.
Campbell, K. S. W., and Bell, M. W. (1977). A primitive amphibian
from the Late Devonian of New South Wales. Alcheringa 1,
369-381.
Carroll, R. L. (1988). "Vertebrate Paleontology and Evolution."
Freeman, New York.
Carroll, R. L. (1992). The primary radiation of terrestrial vertebrates.
Annu. Rev. Earth Planet. Sei. 20, 45 - 84.
Chang, M. M. (1982). The braincase of Youngolepis, a Lower Devonian crossopterygian from Yunnan, South-Western China.
Ph.D. Thesis, University of Stockholm.
Chang, M. M. (1991a). Head exoskeleton and shoulder girdle of
Youngolepis. In "Early Vertebrates and Related Problems of Evolutionary Biology" (M. M. Chang, Y. H. Liu, and G. R. Zhang,
eds.), pp. 355-378. Science Press, Beijing.
Chang, M. M. (1991b). "Rhipidistians," dipnoans and tetrapods.
In "Origins of the Higher Groups of Tetrapods: Controversy
and Consensus" (H.-P. Schultze and L. Trueb, eds.), pp. 3-28.
Cornell University Press (Comstock), Ithaca, NY.
Chang, M. M., and Smith, M. M. (1992). Is Youngolepis a porolepiform? J. Vertebr. Paleontol. 12, 294-312.
Chang, M. M., and Yu, X. (1984). Structure and phylogenetic significance of Diabolichthys speratus gen. et sp. nov., a new dipnoan-like form from the Lower Devonian of Eastern Yunnan,
China. Proc. Linn. Soc. N. S. W. 107, 171 - 184.
Chang, M. M., and Zhu, M. (1993). A new Middle Devonian osteolepidid from Qujing, Yunnan. Mem. Assoc. Australas. Palaeontol. 15, 183-198.
Chorn, J., and Schultze, H.-P. (1989). A complete specimen of
Sagenodus (Dipnoi) from the Upper Pensylvanian of the Hamilton quarry, Kansas. In "Regional Geology and Paleontology of
Upper Paleozoic Hamilton Quarry Area in Southeastern Kansas" (G. Mapes and R. Mapes, eds.), Kans. Geol. Surv. Guidebook Ser. 6, pp. 173-176.
Clack, J. A. (1988). New material of the early tetrapod Acanthostega
from the Upper Devonian of East Greenland. Palaeontology 31,
699-724.
Clack, J. A. (1989). Discovery of the earliest-known tetrapod stapes.
Nature (London) 342, 425 - 430.
Clack, J. A. (1994a). Acanthostega gunnari, a Devonian tetrapod from
Greenland; the snout, palate and ventral parts of the braincase,
with a discussion of their significance. Medd. Gronl. Geosci.
31, 1-24.
Clack, J. A. (1994b). Earliest known tetrapod braincase and the
evolution of the fenestra ovalis. Nature (London) 369, 392-394.
Cloutier, R. (1990). Phylogenetic interrelationships of the actinistians (Osteichthyes: Sarcopterygii): Patterns, trends, and rates
of evolution. Ph.D. Thesis, University of Kansas, Lawrence.
Cloutier, R. (1991a). Interrelationships of Palaeozoic actinistians:
Patterns and trends. In "Early Vertebrates and Related Problems
of Evolutionary Biology" (M. M. Chang, Y. H. Liu, and G. R.
Zhang, eds.), pp. 379-428. Science Press, Beijing.
Cloutier, R. (1991b). Patterns, trends and rates of evolution within
the Actinistia. Environ. Biol. Fishes 32, 23-58.
Cloutier, R., (1996a). The primitive actinistian Miguashaia bureaui
Schultze (Sarcopterygii). In "Devonian Fishes and Plants from
Miguasha, Quebec, Canada" (H.-P. Schultze and R. Cloutier,
eds.), pp. 227-247. Verlag Dr. Freidrich Pfeil, Munich.
Cloutier, R., (1996b). Dipnoi: Sarcopterygii). In "Devonian Fishes
and Plants from Miguasha, Quebec, Canada" (H.-P. Schultze
and R. Cloutier, eds.), pp. 198-226. Verlag Dr. Friedrich
Pfeil, Munich.
Cloutier, R., and Forey, P. L. (1991). Diversity of extinct and living
actinistian fishes (Sarcopterygii). Environ. Biol. Fishes 32, 5974.
Cloutier, R., and Schultze, H.-P. (1996). Porolepiforms fishes (Sarcopterygii). In "Devonian Fishes and Plants from Miguasha,
Quebec, Canada" (H.-P. Schultze and R. Cloutier, eds.),
pp. 248-270. Verlag Dr. Friedrich Pfeil, Munich.
Cloutier, R., Smith, M. M., and Krupina, N. I. (1993). Growth of
the dental system of the Famennian dipnoan, Andreyevichthys
epitomus from Russia: Morphometrics and morphogenesis of the
entopterygoid tooth plate. In "The Gross Symposium. Scientific
Sessions: Abstracts" (S. Turner, ed.). Universitè des Sciences
et Technologies de Lille, Villeneuve d'Ascq, France.
Cloutier, R., Loboziak, S., Candilier, A.-M., and Blieck, A., (1996).
Biostratigraphy of the Upper Devonian Escuminac Formation,
eastern Québec, Canada: A comparative study based on miospores and fishes. Rev. Palaeobot. Palynol (in press).
Coates, M. I. (1991). New palaeontological contributions to limb
ontogeny and phylogeny. In "Developmental Patterning of the
Vertebrate Limb" (J. R. Hinchliffe, J. M. Hurle, and D. Summerbell, eds.), pp. 325-337. Plenum, New York.
Coates, M. I. (1995). The origin of vertebrate limbs. In "The Evolution of Developmental Mechanisms" (M. Akam, P. W. H. Holland, P. W. Ingham, and G. A. Wray, eds.), pp. 169-180. The
Company of Biologists Limited, Cambridge, UK.
Coates, M. I., and Clack, J. A. (1990). Polydactyly in the earliest
known tetrapod limbs. Nature (London) 347, 66-69.
Coates, M. I., and Clack, J. A. (1991). Fish-like gills and breathing
in the earliest known tetrapod. Nature (London) 352, 234-235.
Cope, E. D. (1889). Synopsis of the families of Vertebrata. Am. Nat.
23, 849-877.
Daeschler, E. B., Shubin, N. H., Thomson, K. S., and Amaral,
W. W. (1994). A Devonian tetrapod from North America. Science
265, 639-642.
Denison, R. H. (1968a). Early Devonian lungfishes from Wyoming,
Utah and Idaho. Fieldiana, Geol. 17, 353-413.
Denison, R. H. (1968b). The evolutionary significance of the earliest
known lungfish, Uranolophus. In "Current Problems of Lower
Vertebrate Phylogeny" (T. (rvig, ed.), Nobel Symp. 4,
pp. 247-258. Almqvist & Wiksell, Stockholm.
De Queiroz, K., and Gauthier, J. (1990). Phylogeny as a central
principle in taxonomy: Phylogenetic definitions of taxon names.
Syst. Zool. 39, 307 - 322.
17. Interrelationships of Basal Sarcopterygians Dollo, L. (1895). Sur la phylogénie des Dipneustes. Bull. Soc. Belge
Géol. Paléontol. Hydrol. 9, 79-128.
Donoghue, M. J., Doyle, J. A., Gauthier, J., Kluge, A. G., and Rowe,
T. (1989). The importance of fossils in phylogeny reconstruction.
Annu. Rev. Ecol. Syst. 20, 431-460.
Doyle, J. A., and Donoghue, M. J. (1986). Seed plant phylogeny
and the origin of angiosperms: An experimental cladistic approach. Bot. Rev. 52, 321-431.
Doyle, J. A., and Donoghue, M. J. (1987). The importance of fossils
in elucidating seed plant phylogeny and macroevolution. Rev.
Palaeobot. Palynol. 50, 63-95.
Etheridge, R. (1906). The cranial buckler of a dipnoan fish, probably
Ganorhynchus, from the Devonian beds of the Murrumbidgee
River, New South Wales. Rec. Aust. Mus. 6, 129-132.
Forey, P. L. (1980). Latimeria: A paradoxical fish. Proc. R. Soc. London,
Ser. B 208, 369-384.
Forey, P. L. (1981). The coelacanth Rhabdoderma in the Carboniferous of the British Isles. Palaeontology 24, 203-229.
Forey, P. L. (1984). The coelacanth as a living fossil. In "Living
fossils" (N. Eldredge and S. M. Stanley, eds.), pp. 166-169.
Springer-Verlag, New York.
Forey, P. L. (1987). Relationships of lungfishes. J. Morphol., Suppl.
1, 75-91.
Forey, P. L. (1991). Latimeria chalumnae and its pedigree. Environ.
Biol. Fishes 32, 75-97.
Forey, P. L., Gardiner, B. G., and Patterson, C. (1991). The lungfish,
the coelacanth and the cow revisited. In "Origins of the Higher
Groups of Tetrapods: Controversy and Consensus" (H.-P.
Schultze and L. Trueb, eds.), pp. 145-172. Cornell University
Press (Comstock), Ithaca, NY.
Forster-Cooper, C. (1937). The Middle Devonian fish fauna of Achanarras. Trans. R. Soc. Edinburgh 59, 223-240.
Fricke, H., Reinicke, O., Hofer, H., and Nachtigall, W. (1987).
Locomotion of the coelacanth Latimeria chalumnae in its natural
environment. Nature (London) 329, 331-333.
Fritzsch, B. (1987). The inner ear of the coelacanth fish Latimeria
has tetrapod affinities. Nature (London) 327, 153-154.
Fritzsch, B. (1988). Phylogenetic and ontogenetic origin of the dorsolateral auditory nucleus of anurans. In "The Evolution of the
Amphibian Auditory System" (B. Fritzsch, M. Ryan, W. Wilsczynski, W. Hetherington, and T. Walkowiak, eds.), pp. 561586. Wiley, New York.
Fritzsch, B. (1992). The water-to-land transition: Evolution of the
tetrapod basilar papilla, middle ear, and auditory nuclei. In "The
Evolutionary Biology of Hearing" (D. B. Webster, R. R. Fray, and
A. N. Popper, eds.), pp. 351-375. Springer-Verlag, New York.
Gaffney, E. S. (1979). Tetrapod monophyly: A phylogenetic analysis. Bull. Carnegie Mus. Nat. Hist. 13, 92-105.
Gardiner, B. G. (1980). Tetrapod ancestry: A reappraisal. In "The
Terrestrial Environment and the Origin of Land Vertebrates"
(A. L. Panchen, ed.), pp. 177-185. Academic Press, London.
Gardiner, B. G. (1984). The relationships of the palaeoniscid fishes,
a review based on new specimens of Mitnia and Moythomasia
from the Upper Devonian of Western Australia. Bull. Br. Mus.
(Nat. Hist.), Geol. 37(4), 173-428.
Gardiner, B. G., Janvier, P., Patterson, C., Forey, P. L., Greenwood,
H., Miles, R. S., and Jefferies, R. P. S. (1979). The salmon,
the lungfish and the cow: A reply. Nature (London) 277, 175-176.
Gauthier, J., Kluge, A. G., and Rowe, T. (1988). Amniote phylogeny
and the importance of fossils. Cladistics 4, 105-209.
Gill, T. (1872). Arrangement of the families of fishes. Stnithson.
Misc. Collect. 11, I-XLVI, 1-49.
Goodrich, E. S. (1902). On the pelvic girdle and fin of Eus thenopteron.
J. Microsc. Soc. 45, 311-324.
471
Gorr, T., Kleinschmidt, T., and Fricke, H. (1991). Close tetrapod
relationships of the coelacanth Latimeria indicated by haemoglobin sequences. Nature (London) 351, 394-395.
Greenwood, P. H. (1987). The natural history of African lungfishes.
Morphol., Suppl. 1, 163-179.
Gross, W. (1941). Über den Unterkiefer einiger devonischer Crossopterygier. Abh. Preuss. Akad. Wiss., Mat.-Naturwiss. Kl. pp.
1-51.
Halstead, L. B. (1978). The cladistic revolution-can it make the
grade? Nature (London) 276, 759.
Halstead, L. B., White, E. I., and MacIntyre, G. T. (1979). L. B.
Halstead and colleagues reply Nature (London) 277, 176.
Harland, W. B., Armstrong, R. L., Cox, A. V., Craig, L. E., Smith,
A. G., and Smith, D. G. (1990). A Geologic Time Scale 1989.
Cambridge University Press, Cambridge, UK.
Hedges, S. B., Hass, C. A., and Maxson, L. R. (1993). Relations of
fish and tetrapods. Nature (London) 363, 501-502.
Holmes, E. B. (1985). Are lungfishes the sister group of tetrapods?
Biol. J. Linn. Soc. 25, 379-397.
Huelsenbeck, J. P. (1991). When are fossils better than extant taxa
in phylogenetic analyses? Syst. Zool. 40, 458-469.
Huxley, T. H. (1861). Preliminary essay upon the systematic arrangement of the fishes of the Devonian epoch. Mem. Geol. Surv.
U.K., Figures and Descr. Br. Org. Remains 10, 1-40.
Janvier, P. (1980). Osteolepid remains from the Devonian of the
Middle East, with particular reference to the endoskeletal shoulder girdle. In "The Terrestrial Environment and the Origin of
Land Vertebrates" (A. L. Panchen, cd.) pp. 223-254. Academic
Press, London.
Jarvik, E. (1937). On the species of Eusthenopteron found in Russia
and the Baltic states. Bull. Geol. Inst. Univ. Uppsala 27, 63127.
Jarvik, E. (1942). On the structure of the snout of crossopterygians
and lower gnathostomes in general. Zool. Bidr. Uppsala 21,
235-675.
Jarvik, E. (1944a). On the dermal bones, sensory canais and pitlines of the skull in Eusthenopteron foordi Whiteaves, with some
remarks on E. sâve-siiderberghi Jarvik. K. Sven. Vetenskapsalcad.
Handl. [3] 21(3), 1-48.
Jarvik, E. (1944b). On the exoskeletal shoulder-girdle of teleostomian fishes, with special reference to Eusthenopteron foordi Whiteaves. K. Sven. Vetenskapsakad. Handl. [3] 21(7), 1-32.
Jarvik, E. (1948). On the morphology and taxonomy of the Middle
Devonian osteolepid fishes of Scotland. K. Sven. Vetenskapsakad.
Handl. [3] 25, 1-301.
Jarvik, E. (1952). On the fish-like tail in the ichthyostegid stegocephalians. Medd. Groenl. 114, 1-90.
Jarvik, E. (1954). On the visceral skeleton in Eusthenopteron with a
discussion of the parasphenoid and palatoquadrate in fishes.
Sven. Vetenskapsakad. Handl. [4] 5, 1-104.
Jarvik, E. (1963). The composition of the intermandibular division
of the head in fish and tetrapods and the diphyletic origin of
the tetrapod tongue. K. Sven. Vetenskapsakad. Handl. [4] 9, 1-74.
Jarvik, E. (1964). Specializations in early vertebrates. Ann. Soc. R.
Zool. Belg. 94, 11-95.
Jarvik, E. (1972). Middle and Upper Devonian Porolepiformes from
East Greenland with special reference to Glyptolepis groenlandica
n. sp. Medd. Groenl. 187, 1-295.
Jarvik, E. (1980). "Basic Structure and Evolution of Vertebrates,"
Vol. 1. Academic Press, London.
Jessen, H. (1966). Die Crossopterygier des Oberen Plattenkalkes
(Devon) der Bergisch-Gladbach-Paffrather Mulde (Rheinisches
Schiefergebirge) unter Berücksichtigung von amerikanischem
und europâischem Onychodus-material. Ark. Zool. [2] 18,
305-389.
472
RICHARD CLOUTIER AND PER ERIK AHLBERG
Jessen, H. (1975). A new choanate fish, Powichthys thorsteinssoni
n.g. n.sp., from the early Lower Devonian of the Canadian
Arctic Archipelago. Colloq. Int. C. N. R. S., 218, 213-222.
Jessen, H. (1980). Lower Devonian Porolepiformes from the Canadian Arctic with special reference to Powichthys thorsteinssoni
Jessen. Palaeontographica, Abt. A 167, 180-214.
Jurgens, J. D. (1973). The morphology of the nasal region of Amphibia and its bearing on the phylogeny of the group. Ann.
Univ. Stellenbosch, Ser. A 46, 3-136.
Kemp, A. (1987). The biology of the Australian lungfish, Neoceratodus forsteri (Krefft 1870). J. Morphol., Suppl. 1, 181-198.
Lambers, P. (1992). On the ichthyofauna of the Solnhofen Lithographie Limestone (Upper Jurrasic, Germany). Ph.D. Dissertation, Rijksuniversiteit Groningen, Groningen, The Netherlands.
Lauder, G. V. (1980). On the evolution of jaw adductor musculature
in primitive gnathostome fishes. Breviora 460, 1-10.
Lebedev, O. A. (1984). The first find of a Devonian tetrapod in the
U.S.S.R. Dokl. Akad. Nauk SSSR 278, 1407-1473.
Lebedev, O. A. (1995). Morphology of a new osteolepidid fish from
Russia. Bull. Mus. Natl. Hist. Nat., Sect. C, [4] 17, 287-341.
Lebedev, O. A., and Clack, J. A. (1993). Devonian tetrapod remains
from Andreyevka, Tula, Russia. Palaeontology 36, 721-734.
Lebedev, O. A., and Coates, M. I. (1995). The postcranial skeleton
of the Devonian tetrapod Tulerpeton curtum Lebedev. Zool. I.
Linn. Soc. 114, 307-348.
Leonardi, G. (1983). Notopus petri nov. gen., nov. sp.: Une empreinte d'amphibien du Dévonien au Parana'. (Brésil). Geobios
16, 233-239.
Long, J. A. (1985). The structure and relationships of a new osteolepiform fish from the Late Devonian of Victoria, Australia.
Alcheringa 9, 1-22.
Long, J. A. (1987). An unusual osteolepiform fish from the Late
Devonian of Victoria, Australia. Palaeontology 30, 839-852.
Long, J. A. (1988a). Late Devonian fishes from Gogo, Western
Australia. Natl. Geogr. Res. 4, 436-450.
Long, J. A. (1988b). New palaeoniscoid fishes from the Late Devonian and Early Carboniferous of Victoria. Mem. Assoc. Australas.
Palaeontol. 7, 1-64.
Long, J. A. (1989). A new rhizodontiform fish from the Early Carboniferous of Victoria, Australia, with remarks on the phylogenetic position of the group. I. Vertebr. Paleontol. 9, 1-17.
Long, J. A. (1991). Arthrodire predation by Onychodus (Pisces, Crossopterygii) from the Late Devonian Gogo Formation, Western
Australia. Rec. West. Aust. Mus. 15, 479-481.
Long, J. A. (1992). Cranial anatomy of two new Late Devonian
lungfishes (Pisces: Dipnoi) from Mt. Howitt, Victoria. Rec. Aust.
Mus. 44, 299-318.
Long, J. A. (1993). Cranial ribs and the origin of dipnoan air-breathing. Mem. Assoc. Australas. Palaeontol. 15, 199-209.
Lovtrup, S. (1977). "The Phylogeny of Vertebrata." Wiley, London.
Lund, R. (1970). Fossil fishes from Southwestern Pennsylvania.
Part I: Fishes from the Duquesne Limestones (Conemaugh,
Pennsylvania). Ann. Carnegie Mus. 44, 71-101.
Lund, R., and Lund, W. L. (1984). New genera of coelacanths from
the Bear Gulch Limestone (Lower Carboniferous) of Montana
(U.S.A.). Geobios 17(2), 237-244.
Lund, R., and Lund, W. L. (1985). Coelacanths from the Bear Gulch
Limestone (Namurian) of Montana and the evolution of the
Coelacanthiformes. Bull. Carnegie Mus. Nat. Hist. 25, 1-74.
Lund, W. L., Lund, R., and Klein, G. A. (1985). Coelacanth feeding
mechanisms and ecology of Bear Gulch coelacanths. C. R. Neuvi.
Congr. Int. Stratigr. Géol. Carbonifère 5, 492-500.
Lyarskaya, L. A. (1981). Baltic Devonian Placodermi Asterolepididae. Zinatne, Riga.
Lyarskaya, L. A., and Mark-Kurik, E. (1972). Eine neue Fundstelle
oberdevonscher Fische im Baltikum. Neues Jahrb. Minerai., Geol.
Palaeontol., Monatsh. 7, 407-414.
Maisey, J. G. (1986a). Heads and tails: A chordate phylogeny. Clad stics 2, 201-256.
Maisey, J. G. (1986b). Coelacanth from the Lower Cretaceous of
Brazil. Am. Mus. Novit. 2866, 1-30.
Marshall, C. R. (1987). Lungfish: Phylogeny and parsimony. J.
Morphol., Suppl. 1, 151-162.
Marshall, C. R., and Schultze, H.-P. (1992). Relative importance of
molecular, neontological, and paleontological data in understanding the biology of the vertebrate invasion of land. J. Mol.
Evol. 35, 93-101.
Meyer, A. (1995). Molecular evidence on the origin of tetrapods
and the relationships of the coelacanth. Trends Ecol. Evol.
10(3), 95-136.
Meyer, A., and Wilson, A. C. (1990). Origin of tetrapods inferred
from their mitochondrial DNA affiliation to lungfish. J. Mol.
Evol. 31, 359-364.
Meyer, A., and Wilson, A. C. (1991). Coelacanth's relationships.
Nature (London) 353, 19.
Miles, R. S. (1975). The relationships of the Dipnoi. Colloq. Int.
C. N. R. S. 218, 133-148.
Miles, R. S. (1977). Dipnoan (lungfish) skulls and the relationships
of the group: A study based on new species from the Devonian
of Australia. Zool. I. Linn. Soc. 61, 1-328.
Miller, H. (1841). "The Old Red Sandstone or New Walks in an
Old Field." Johnstone, Edinburgh.
Milner, A. R., Smithson, T. R., Milner, A. C., Coates, M. I., and
Rolfe, W. D. I. (1986). The search for early tetrapods. Mod. Geol.
10, 1-28.
Millot, J., and Anthony, J. (1958). "Anatomie de Latimeria chalumnae," Tome I. Squelette et muscles. CNRS, Paris.
Moy-Thomas, J. A., and Miles, R. S. (1971). "Palaeozoic Fishes,"
2nd ed. Chapman & Hall, London.
Murchison, R. I. (1839). "The Silurian System." John Murray,
London.
Normark, B. B., McCune, A. R., and Harrison, R. G. (1991). Phylogenetic relationships of neopterygian fishes, inferred from mitochondrial DNA sequences. Mol. Biol. Foui. 8, 819-834.
Northcutt, R. G., and Bemis, W. E. (1993). Cranial nerves of the
coelacanth, Latimeria chalumnae (Osteichthyes: Sarcopterygii: Actinistia) and comparisons with other Craniata. Brain, Behav. Evol.
42, Suppl. 1, 1-75.
Obruchev, D. (1933). Description of four new fish species from the
Devonian of Leningrad Province. Mater. Cent. Sci. Geol. Prospect.
Inst., Palaeontol. Stratigr. Mag. 1, 12-14.
Orvig, T. (1957). Remarks on the vertebrate fauna of the Lower
Upper Devonian of Escuminac Bay, P.Q., Canada, with special
reference to the porolepiform crossopterygians. Ark. Zool. [2]
10, 367-426.
Orvig, T. (1969). Vertebrates from the Wood Bay group and the
position of the Emsian-Eifelian boundary in the Devonian of
Vestspitsbergen. Lethaia 2(4), 273-319.
Orvig, T. (1986). A vertebrate bone from the Swedish Palaeocene.
Geol. Foeren. Stockholm Foerh. 108, 139-141.
Owen, R. (1846). "Lectures on the Comparative Anatomy and Physiology of the Vertebrate Animals," Part I. Longman, Brown,
Green and Longman, London.
Owen, R. (1860). "Palaeontology, or a Systematic Summary of Extinct Animals and their Geological Relations." Black, Edinburgh.
Panchen, A. L. (1985). On the amphibian Crassigyrinus scoticus Watson from the Carboniferous of Scotland. Philos. Trans. R. Soc.
London Ser. B 309, 461-568.
17. Interrelationships of Basal Sarcopterygians Panchen, A. L., and Smithson, T. R. (1987). Character diagnosis,
fossils, and the origin of tetrapods. Biol. Rev. Cambridge Philos.
Soc. 62, 341-438.
Panchen, A. L., and Smithson, T. R. (1988). The relationships of
the earliest tetrapods. In "The Phylogeny and Classification of
the Tetrapods" (M. J. Benton, ed.) Vol. 1, pp. 1-32. Oxford
University Press (Clarendon), Oxford.
Patterson, C. (1980). Origin of tetrapods: historical introduction to
the problem. In "The Terrestrial Environment and the Origin of
Land Vertebrates" (A. L. Panchen, ed.), pp. 159-175. Academic
Press, London.
Patterson, C. (1981). Significance of fossils in determining evolutionary relationships. Annu. Rev. Ecol. Syst. 12, 195-223.
Patterson, C. (1982a). Morphological characters and homology.
Syst. Assoc. Spec. Vol. 21, 21-74.
Patterson, C. (1982b). Classes and cladists or individuals and evolution. Syst. Zool. 31, 284-286.
Patterson; C., and Rosen, D. E. (1977). Review of ichthyodectiform
and other Mesozoic teleost fishes and the theory and practice
of classifying fossils. Bull. Am. Mus. Nat. Hist. 158, 81-172.
Rackoff, J. S. (1980). The origin of the tetrapod limb and the ancestry
of tetrapods. Syst. Assoc. Spec. Vol. 15, 255-292.
Rocek, Z., and Rage, J. C. (1994). The presumed amphibian footprint Noto pus petri from the Devonian: A probable starfish trace
fossil. Lethaia 27, 241-244.
Romer, A. S. (1937). The braincase of the Carboniferous crossopterygian Megalichthys nitidus. Bull. Mus. Comp. Zool. 82, 1-73.
Romer, A. S. (1947). Review of the Labyrinthodontia. Bull. Mus.
Comp. Zool. 99, 7-368.
Romer, A. S. (1966). "Vertebrate Paleontology," 3rd ed. University
of Chicago Press, Chicago.
Rosen, D. E., Forey, P. L., Gardiner, B. G., and Patterson, C.
(1981). Lungfishes, tetrapods, paleontology, and plesiomorphy.
Bull. Am. Mus. Nat. Hist. 167, 159-276.
Sâve-Süderbergh, G. (1932). Preliminary note on Devonian stegocephalians from East Greenland. Medd. Groenl. 94, 1-107.
Schaeffer, B. (1952). Rates of evolution in the coelacanth and dipnoan fishes. Evolution (Lawrence, Kans.) 6, 101-111.
Schoch, R. M. (1986). "Phylogeny Reconstruction in Paleontology."
Van Nostrand-Reinhold, New York.
Schultze, H.-P. (1969). Die Faltenzâhne der rhipidistiiden Crossopterygier, der Tetrapoden und der Actinopterygier-Gattung Lepisosteus. Palaeontogr. Ital. 65 [N. S. 35], 59-137.
Schultze, H.-P. (1970). Folded teeth and the monophyletic origin
of tetrapods. Am. Mus. Novi. 2408, 1-10.
Schultze, H.-P. (1973). Crossopterygier mit heterozerker Schwanzflosse aus dem Oberdevon Kanadas, nebst einer Beschreibungvon Onychodontida-Resten aus dem Mitteldevon Spaniens und
aus dem Karbon der USA. Palaeontographica, Aht. A 143, 188-208.
Schultze, H.-P. (1975). Die Lungenfisch-Gattung Conchopoma
(Pisces, Dipnoi). Senckenbergiana Lethaea 56, 191-231.
Schultze, H.-P. (1977). The origin of the tetrapod limb within the
rhipidistian fishes. In "Major Patterns in Vertebrate Evolution"
(M. K. Hecht, P. C. Goody, and B. M. Hecht, eds.), pp. 541-544.
Plenum, New York.
Schultze, H.-P. (1981). Hennig und der Ursprung der Tetrapoda.
Palaeontol. Zh. 55, 71-86.
Schultze, H.-P. (1985). Reproduction and spawning sites of Rhabdoderma (Pisces, Osteichthyes, Actinistia) in Pennsylvanian deposits of Illinois, USA. C. R. Neuv. Congr. Int. Stratigr. Géol. Carbonifère 5, 326-330.
Schultze, H.-P. (1987). Dipnoans as sarcopterygians. J. Morpho!.
Suppl. 1, 39-74.
Schultze, 1-1.-P. (1991). A comparison of controversial hypotheses
473
on the origins of tetrapods. In "Origins of the Major Groups of
Tetrapods: Controversies and Consensus" (H.-P. Schultze and
L. Trueb, eds.), pp. 29-67. Cornell University Press (Comstock),
Ithaca, NY.
Schultze, H.-P. (1992a). A new long-headed dipnoan (Osteichthyes)
from the Middle Devonian of Iowa, USA. J. Vertebr. Paleontol.
12, 42-58.
Schultze, H.-P. (1992b). Dipnoi. In "Fossilium catalogus I:Animalia" (F. Westphal, ser. cd.), Pars 131. Kugler Publications,
Amsterdam and New York.
Schultze, H.-P. (1993). Osteichthyes: Sarcopterygii. In "The Fossil
Record 2" (M. J. Benton, ed.), pp. 657-663. Chapman & Hall,
London.
Schultze, H.-P. (1994). Comparison of hypotheses on the relationships of sarcopterygians. Syst. Biol. 43, 155-173.
Schultze, H.-P., (1996). The elpistostegid fish Elpistostege, the closest
the Miguasha fauna cornes to a tetrapod. In "Devonian Fishes
and Plants from Miguasha, Quebec, Canada" (H.-P. Schultze
and R. Cloutier, eds.), pp. 316-327. Verlag Dr. Pfeil, München.
Schultze, H.-P., and Arsenault, M. (1985). The panderichthyid fish
Elpistostege: A close relative of tetrapods? Palaeontology 28,
293-309.
Schultze, H.-P., and Campbell, K. S. W. (1987). Characterization
of the Dipnoi, a monophyletic group. J. Morphol. Suppl. 1, 2537.
Schultze, H.-P., and Marshall, C. R. (1993). Contrasting the use of
functional complexes and isolated characters in lungfish evolution. Mem. Assoc. Australas. Palaeontol. 15, 211-224.
Schultze, H.-P., Cloutier, R., and Marshall, C. R. (1993). Contrasting the use of functional complexes and isolated characters in
lungfish evolution. Assoc. Australas. Palaeontol., K. S. W. Campbell
Syinp., Abstr. Vol., p. 21.
Schwimmer, D. R., Stewart, J. D., and Williams, G. D. (1994). Giant
fossil coelacanths of the late Cretaceous in the eastern United
States. Geology 55, 503-506.
Sedgwick, A., and Murchison, R. I. (1828). On the structure and
relations of the deposits contained between the Primary Rocks
and the Oolitic Series in the North of Scotland. Trans. Geo!. Soc.
London [2] 3, 125-160.
Sharp, P. M., Lloyd, A. T., and Higgins, D. G. (1991). Coelacanth's
relationships. Nature (London) 353, 218-219.
Shubin, N. H., and Alberch, P. (1986). A morphogenetic approach
to the origin and basic organization of the tetrapod limb. Evol.
Biol. 20, 319-387.
Smith, M. M. (1984). Petrodentine in extant and fossil dipnoan
dentitions: Microstructure, histogenesis and growth. Proc. Linn.
Soc. N. S. W. 107, 367-407.
Smith, M. M. (1989). Distribution and variation in enamel structure
in the oral teeth of sarcopterygians: its significance for the evolution of a protoprismatic enamel. Hist. Biol. 3, 97-126.
Smith, M. M., and Chang, M. M. (1990). The dentition of Diabolepis
speratus Chang & Yu, with further consideration of its relationships and the primitive dipnoan dentition. J. Vertebr. Paleontol.
10, 420-433.
Smith, M. M., Smithson, T. R., and Campbell, K. S. W. (1987).
The relationships of Uronemus: A Carboniferous dipnoan with
highly modified tooth plates. Philos. Trans. R. Soc. London
317, 299-327.
Smithson, T. R. (1985). On the relationships and morphology of
the Carboniferous amphibian Eoherpeton watsoni. Zool. J. Linn.
Soc. 85, 317-410.
Stensiô, E. (1922). Über zwei Coelacanthiden aus dem Oberdevon
von Wildungen. Palaeontol. Zh. 4, 167-210.
Stensiô, E. (1937). On the Devonian coelacanthids of Germany with
474
RICHARD CLOUTIER AND PER ERIK AHLBERG
special reference to the dermal skeleton. K. Sven. Vetenskapsakad.
Handl. 3(16), 1-56.
Stock, D. W., and Swofford, D. L. (1991). Coelacanth relationships.
Nature (London) 353, 217-218.
Stock, D. W., Moberg, K. D., Maxson, L. R., and Whitt, G. S. (1991).
A phylogenetic analysis of the 18S ribosomal RNA sequence of
the coelacanth Latimeria chalumnae. Environ. Biol. Fishes 32,
99-117.
Stôssel, I. (1995). The discovery of a new Devonian tetrapod trackway in SW Ireland. J. Geol. Soc., London 152, 407-413.
Thomson, K. S. (1973). Observations on a new rhipidistian fish
from the Upper Devonian of Australia. Palaeontographica, Abt.
A 143, 209-220.
Tong-Dzuy Thanh, and Janvier, P. (1990). Les Vertébrés du Dévonien inférieur de Bac Bo oriental (Provinces de Bac Thaï et Lang
Son, Viêt Nam). Bull. Mus. Natl. Hist. Nat., Sect. C [4] 12(2),
143-223.
Tong-Dzuy Thanh, and Janvier, P. (1994). Early Devonian fishes
from Trang Xa (Bac Thai, Vietnam) with remarks on the distribution of the vertebrates in the Song Cau Group. J. Southeast Asian
Earth Sci. 10, 235-243.
Traquair, R. H. (1890). List of the fossil Dipnoi and Ganoidei
of Fife and the Lothians. Proc. R. Soc. Edinburgh 17, 385400.
Trueb, L, and Cloutier, R. (1991). A phylogenetic investigation of
the inter- and intrarelationships of the Lissamphibia (Amphibia:
Temnospondyli). In "Origins of the Higher Groups of Tetrapods: Controversy and Consensus" (H.-P. Schultze and L.
Trueb, eds), pp. 223-313. Cornell University Press (Comstock),
Ithaca, NY.
Vorobyeva, E. I. (1960). New data on the crossopterygian fish genus
Panderichthys from the Devonian of the USSR. Paleontol. Zh.
1, 87-96.
Vorobyeva, E. I. (1962). Rhizodont crossopterygians of the Main
Devonian Field. Tr. Paleontol. Inst. 94, 1-139.
Vorobyeva, E. I. (1971). The ethmoid region of Panderichthys and
some problems of the cranial morphology of crossopterygians.
Tr. Paleontol. Inst. 130, 142-159.
Vorobyeva, E. I. (1977). Morphology and nature of evolution of
crossopterygian fishes. Tr. Paleontol. Instit. 163, 1-239.
Vorobyeva, E. I. (1980). Observations on two rhipidistian fishes
from the Upper Devonian of Lode, Latvia. Zool. J. Linn. Soc.
70, 191-201.
Vorobyeva, E. I. (1986). The current state of the problem of amphibian origin. In "Studies in Herpetology" (Z. Roêek, ed.), pp.
25-28. Charles University, Prague.
Vorobyeva, E. I. (1987). Porolepid crossopterygian from the Middle
Devonian of Estonia. Paleontol. Zh. 1987(1), 76-85.
Vorobyeva, E. I. (1989). Panderichthyida-a new order of Paleozoic
crossopterygian fishes (Rhipidistia). Dokl. Akad. Nauk SSSR
306, 188-189.
Vorobyeva, E. I., and Kuznetsov, A. (1992). The locomotor apparatus of Panderichthys rhombolepis (Gross), a supplement to the
problem of fish-tetrapod transition. In 'Fossil Fishes as Living
Animais" (E. Mark-Kurik, ed.), pp. 131-140. Academy of Sciences of Estonia, Tallinn.
Vorobyeva, E. I., and Lyarskaya, L. A. (1968). Crossopterygian and
dipnoan remains from the Amata beds of Latvia and their burial.
ln "Ocherki po filogenii i sistematike iskopaemykh ryb i beschelyustnykh" (D. V. Obruchev, ed.), pp. 71-86. Nauka, Moscow.
Vorobyeva, E. I., and Schultze, H.-P. (1991). Description and systematics of panderichthyid fishes with comments on their relationship to tetrapods. In "Origins of the Higher Groups of Tetrapods: Controversy and Consensus" (H.-P. Schultze and L.
Trueb, eds.), pp. 68-109. Cornell University Press (Comstock),
Ithaca, NY.
Vorobyeva, E. I., and Tsessarskii, A. A. (1986). On origin of vertebrae in lower tetrapods. Zh. Obshch. Biol. 47, 735-747.
Wang, S., Drapala, V., Barwick, R. E., and Campbell, K. S. W.
(1990). A new Early Devonian lungfish, Sorbitorhynchus deleaskitus n. gen. et sp., from Guangxi, China. Paleobiology 16, 168-169.
Warren, A., Jupp, R., and Bolton, B. R. (1986). Earliest tetrapod
trackway. Alcheringa 10, 183-186.
Warren, J. W., and Wakefield, N. A. (1972). Trackways of tetrapod
vertebrates from the Upper Devonian of Victoria, Australia,
Nature (London) 238, 469-470.
Westoll, T. S. (1938). Ancestry of the tetrapods. Nature (London)
141, 127.
Westoll, T. S. (1949). On the evolution of the Dipnoi. In "Genetics,
Paleontology and Evolution" (G. L. Jepsen, G. G. Simpson,
and E. Mayr, eds.), pp. 121-184. Princeton University Press,
Princeton, INJ.
White, E. I. (1965). The head of Dipterus valenc ennesi. Bull. Br. Mus.
(Nat. Hist.) Geol. 11, 3-45.
Whiteaves, J. F. (1883). On some remarkable fossil fishes from the
Devonian rocks of Scaumenac Bay, P. Q., with descriptions of
a new genus and three new species. Can. Nat. Q. J. Sci. [N.S.J
10, 27-35.
Whiteaves, J. F. (1889). Illustrations of the fossil fishes of the Devonian rocks of Canada. Part II. Trans. R. Soc. Can. 6, 77-96.
Woodward, A. S. (1891). Catalogue of the Fossil Fishes in the British
Museum (Natural History), Part II. Br. Mus. (Nat. Hist.),
London.
Worobjewa, E. (1975). Bemerkungen zu Panderichthys rhombolepis
(Gross) aus Lode in Lettland (Gauja Schichten, Oberdevon).
Neues Jahrb. Minerai., Geol. Palaeontol., Monatsh. 1975, 407414.
Young, G. C., Long, J. A., and Ritchie, A. (1992). Crossopterygian
fishes from the Devonian of Antarctica: Systematics, relationships and biogeographic significance. Rec. Austr. Mus., Suppl.
14, 1-77.
Zhu, M., and Janvier, P. (1994). Un Onychodontide (Vertebrata,
Sarcopterygii) du Dévonien Inférieur de Chine. C. R. Séances
Acad. Sci., Ser. 2 319, 951-956.
Appendix 1: Character List
Cosmine. 0 = absent; 1 present.
Mesh canais. 0 = pore cavity with horizontal
partition; 1 = pore cavity without horizontal
partition.
Condition of scales. 0 = rhombic scales; 1 =
rounded scales.
Peg on rhombic scale. 0 = narrow; 1 = broad.
Boss on internai face of scale. 0 absent; 1 =
present.
Ganoine. 0 = absent; 1 = present.
Acrodin. 0 = absence of acrodin caps on teeth;
1 presence of acrodin caps on teeth.
Marginal teeth on dentary. 0 = present; 1 =
absent.
9. Dental plate. 0 = denticles on entopterygoid,
or naked bone; 1 = tooth plate on entopterygoid; 2 = dentine plate on entopterygoid.
17. Interrelationships of Basal Sarcopterygians Dentition on coronoids. 0 = narrow marginal
tooth row; 1 = broad marginal "tooth field."
Spiral parasymphysial teeth. 0 = absent; 1 =
present.
Fang pairs in inner tooth arcade. 0 = absent;
1 = present.
Fang pair on anterior end of dentary. 0 = absent; 1 = present.
Plicidentine. 0 = absent; 1 = polyplocodont
plicidentine; 2 = dendrodont plicidentine.
Skull shape. 0 = lateral orbits, interorbital
skull roof wide and arched; 1 = dorsal orbits,
interorbital skull roof narrow and flat or
concave.
Premaxilla. 0 = present; 1 = absent.
Position of premaxilla. 0 = marginal; 1 = ventral part turned in.
Position of premaxilla. 0 = premaxilla forming
part of orbit; 1 = premaxilla flot forming part
of orbit.
Maxilla. 0 = present; 1 = absent.
Posterodorsal process of maxilla. 0 = present;
1 = absent.
Shape of posterodorsal process of maxilla. 0 =
smooth, convex posterodorsal margin; 1 = distinct posterodorsal angle.
Position of median rostral. 0 = rostral does flot
contribute to jaw margin; 1 = rostral contributes to jaw margin.
Postrostrals. 0 = postrostral mosaic of small
variable bones; 1 = large median postrostral,
with or without accessory bones.
Paired nasals meeting in midline of skull. 0
absent; 1 = present.
Paired frontals. 0 = absent; 1 = present.
E-bone. 0 = absent; 1 = present.
C-bone. 0 = absent; 1 = present.
Supraorbitals. 0 = absent; 1 = present.
Number of supraorbitals (including the "posterior tectal" of Jarvik). 0 = one; 1 = two; 2 =
more than two.
B-bone. 0 = absent; 1 = present.
Position of anterior margin of parietal. 0 = between or in front of orbits; 1 = slightly posterior to orbits; 2 = much posterior to orbits.
Pineal opening. 0 = open; 1 = closed.
Median supraorbital ridges ("eyebrows"). 0 =
absent; 1 = present.
Parietal-supraorbital contact. 0 = absent; 1 =
present.
Extratemporal. 0 = absent; 1 = present.
Intertemporal. 0 = present; 1 = absent.
Supratemporal series. 0 = single bone which
contacts the extrascapular posteriorly and the
475
intertemporal or dermosphenotic anteriorly;
1 = two bones (supratemporal and tabular)
between extrascapular and intertemporal or
postorbital; 2 = single bone (probably the
tabular) in posterior position, bounded
anteriorly by lateral extension of
postparietal.
Spiracle. 0 = small hole on kinetic margin between skull roof and cheek; 1 = large, posteriorly open notch.
Extrascapulars. 0 = present; 1 = absent.
40. Number of extrascapulars. 0 = four; 1 = two;
2 = three; 3 = five.
41. Median extrascapular overlap. 0 = median extrascapular overlapped by lateral extrascapulars; 1 = median extrascapular overlaps the lateral extrascapulars; 2 = median extrascapular
abuts the lateral extrascapulars.
Tectals. 0 = absent; 1 = present.
Number of tectals (not counting the "posterior
tectal" of Jarvik; see char. 29). 0 = one; 1 =
three or more.
Anterior and posterior nares. 0 = both present; 1 = only anterior naris present.
Position of posterior naris. 0 = external, far
from jaw margin; 1 = external, close to jaw
margin; 2 = palatal (palatal posterior flans of
lungfishes deemed nonhomologous with tetrapod choana).
Position of posterior naris. 0 = associated with
the orbit; 1 = flot associated with the orbit.
Position of anterior flans. 0 = facial; 1 = marginal; 2 = palatal.
Palatal opening ("choana") surrounded by premaxilla, maxilla, dermopalatine, and vomer.
0 = absent; 1 = present.
Number of sclerotic plates. 0 = four or less;
1 = more than four.
Condition of lacrimal and jugal. 0 = separate
bones; 1 = fused together.
Prespiracular. 0 = absent; 1 = present.
Dermohyal. 0 = present; 1 = absent.
Postspiracular. 0 = absent; 1 = present.
Squamosal and preopercular. 0 = one bone
("preopercular"); 1 = two separate bones.
Subsquamosals. 0 = absent; 1 = present.
Preopercular-maxillary contact. 0 = preopercular contacts maxilla (if maxilla absent, preopercular reaches ventral margin of cheek); 1 = preopercular does not contact maxilla (if maxilla
absent, preopercular does not reach ventral
margin of cheek).
Quadratojugal. 0 = present, small; 1 = present, large; 2 = absent.
476
RICHARD CLOUTIER AND PER ERIK AHLBERG
Jugal-quadratojugal contact. 0 absent; 1 =
present.
Preoperculosubmandibular. 0 = absent; 1 =
present.
Opercular. 0 = present; 1 = absent.
Subopercular. 0 = present; 1 = absent.
Branchiostegal rays. 0 = present; 1 = absent.
Number of branchiostegal rays per side. 0 =
10 or more; 1 = two to seven; 2 = one.
Submandibulars. 0 = absent; 1 = present.
Width of submandibulars. 0 = narrow; 1 =
broad.
Median gular. 0 = present; 1 absent.
Relative size of median gular. 0 = small; 1 =
large.
Lateral gular. 0 present; 1 = absent.
Size of lateral gular. 0 = lateral gular and branchiostegal rays of similar size; 1 lateral gular
covering approximately half the intermandibular space.
Posterior process of vomer. 0 = absent; 1 =
present.
Articulation of vomer. 0 vomers do not articulate with each other; 1 = vomers articulate
with each other.
Articulation of pterygoid. 0 = pterygoids do
not articulate with each other; 1 = pterygoids
articulate with each other.
Articulation of parasphenoid. 0 = parasphenoid not sutured to vomer; 1 = parasphenoid
sutured to vomer.
Denticulated spiracular groove on parasphenoid. 0 present; 1 absent.
Buccohypophysial foramen of parasphenoid.
0 = single; 1 = double.
Rostral organ. 0 = absent; 1 = present.
Rostral tubuli. 0 = absent; 1 = present.
Fossa autopalatina. 0 = absent; 1 = present.
Paired intervomerine pits. 0 = absent; 1 =
present.
Labial cavity. 0 = absent; 1 = present.
Dermal joint between parietal and postparietal.
0 = absent; 1 = present.
Dorsal endoskeletal articulation between otoccipital and ethmosphenoid blocks of braincase.
0 = absent; 1 = present.
Ventral endoskeletal articulation between otoccipital and ethmosphenoid blocks of braincase.
0 = absent; 1 = present.
Basicranial fenestra with arcual plates. 0 = absent; 1 = present.
Unconstricted cranial notochord. 0 = absent;
1 = present.
Otico-sphenoid bridge. 0 = present; 1 =
absent.
Position of intracranial joint relative to cranial
nerves. 0 = joint passes through profundus foramen; 1 = joint passes through trigeminal foramen.
Condition of hyomandibular. 0 hyomandibular with one proximal articular head; 1 = hyomandibular with two proximal articular heads.
Posttemporal fossae. 0 = absent; 1 = present.
Postorbital process on braincase (equivalent to
character A3 of Chang and Smith, 1992). 0 =
present; 1 = absent.
Dentary. 0 = long; 1 = short.
92. Anterior end of dentary. 0 not modified;
1 = modified into support for parasymphysial
tooth whorl.
93. Number of infradentaries. 0 = one; 1 = two;
2 = four.
Number of coronoids. 0 = four or more; 1 =
three; 2 = two.
Condition of most posterior coronoid. 0 = not
distinctly differentiated from other coronoids;
1 = well developed and oriented vertically.
Prearticular position. 0 = at posterior end of
coronoid series, contacts dentary dorsally; 1 =
ventral to the coronoid series, does not contact
the dentary dorsally.
Articulation of symplectic with articular. 0 =
absent; 1 = present.
Trajectory of supraorbital canal. 0 = canal passing between anterior and posterior nares; 1 =
canal passing anterior to both nares.
Contact of supraorbital canal. 0 = supraorbital
and infraorbital canals in contact rostrally; 1 =
canals not in contact rostrally.
Relationship of infraorbital canal to premaxilla.
0 = infraorbital canal enters premaxilla; 1 = infraorbital canal follows dorsal margin of premaxilla.
Trajectory of otic canal. 0 = otic canal does not
pass through growth center of postparietal;
1 = otic canal passes through growth center of
postparietal.
Contact of otic canal. 0 = otic canal not joining
supraorbital canal; 1 = otic canal joining supraorbital canal.
Position of anterior pit line. 0 = anterior pit
line on postparietal; 1 = anterior pit line on parietal.
104. Position of posterior pit line. 0 = posterior pit
line on posterior half of postparietal; 1 = posterior pit line on anterior half of postparietal.
17. Interrelationships of Basal Sarcopterygians Preopercular canal. 0 = preopercular canal
ends at dorsal margin of preopercular; 1 = canal does not end at dorsal margin of preopercular.
Jugal canal. 0 = absent; 1 = present.
Position of infraorbital canal. 0 = ventral to anterior flans; 1 = dorsal to anterior naris.
Pit lines of lower jaw. 0 = middle pit line not
developed into enclosed canal ("oral canal");
1 = middle pit line developed into enclosed
oral canal or intermediate morphology.
Pit line of lower jaw. 0 = anterior pit line flot
developed into enclosed canal; 1 = anterior pit
line developed into enclosed canal linking oral
and mandibular canals.
Trajectory of mandibular canal. 0 = mandibular canal passing through dentary; 1 = mandibular canal flot passing through dentary.
Trajectory of mandibular canal. 0 = mandibular canal passing through most posterior infradentary; 1 = mandibular canal not passing
through most posterior infradentary.
Anocleithrum. 0 = element developed as postcleithrum; 1 = element developed as anocleithrum sensu stricto; 2 = element absent.
Condition of anocleithrum/postcleithrum. 0 exposed on surface; 1 = subdermal.
Depressed lamina of cleithrum. 0 = absent;
1 = present.
Dorsal end of cleithrum. 0 = pointed; 1 =
broad and rounded.
Relationship of clavicle to cleithrum. 0 = ascending process of clavicle overlaps cleithrum
laterally; 1 = ascending process of clavicle
wraps round anterior edge of cleithrum, overlapping it both laterally and mesially.
Extracleithrum. 0 = absent; 1 = present.
Interclavicle. 0 = present; 1 = absent.
Proximal articular surface of humerus. 0 = concave; 1 = flat; 2 = convex.
Endoskeletal supports in pectoral fins. 0 =
multiple elements articulating with girdle; 1 single element ("humerus") articulating with
girdle.
Entepicondylar foramen. 0 = absent; 1 =
present.
Deltoid and supinator processes. 0 = absent;
1 = present.
Number of mesomeres in pectoral fin. 0 =
three to five; 1 = seven or more.
Trifurcations in pectoral fin skeleton (i.e.,
mesomeres carrying both pre- and postaxial radials). 0 = absent; 1 = present.
477
Digits. 0 = absent; 1 = present.
Pelvis contacting vertebral column. 0 = no;
1 = yes.
Dorsal and anal fins. 0 = present; 1 = absent.
Basal plates in dorsal fin supports. 0 = absent;
1 = present.
Anterior dorsal fin support. 0 = separate radials and basal plate; 1 = single element.
Posterior branched radial complex in posterior
dorsal fin. 0 = absent; 1 = present.
Basal scutes on fins. 0 = absent; 1 = present.
Relative length of proximal unsegmented part
of lepidotrichium. 0 = much less than segmented part; 1 = similar to segmented part;
2 = much greater than segmented part.
Distal end of lepidotrichium. 0 = branched;
1 = single.
Epichordal lepidotrichia in tail. 0 = absent;
1 = present.
Relative size of epichordal and hypochordal
lepidotrichia. 0 = epichordals less developed
than hypochordals; 1 = epichordals and hypochordals equally developed; 2 = epichordals
more developed than hypochordals.
Neural arches. 0 = bilateral halves of neural
arch separated; 1 = halves fused.
Supraneural spines. 0 = present on thoracic
and abdominal vertebrae; 1 = restricted to a
few vertebrae at anterior end of column, or
absent.
Condition of intercentra. 0 = ossified; 1 = not
ossified.
Condition of pleurocentra. 0 = flot ossified;
1 = ossified.
Ribs. 0 = absence of well-ossified ribs; 1 =
presence of well-ossified ribs.
Appendix 2: List of Genera Used in the
Phylogenetic Ana lysis
The genera are entered into the data set in alphabetical order so as to preclude any bias toward preconceived groupings during the phylogenetic analysis.
The tetrapods, actinistians, and dipnoans included
in the analysis are all stem-group members except
Crassigyrinus, which is a probable crown tetrapod
(Lebedev and Coates, 1995).
Acanthostega: Late Devonian (Famennian) tetrapod
from eastern Greenland. Most of the skeleton is
known.
Allenypterus: Early Carboniferous (Namurian) actinishan from Montana. Represented by complete, laterally compressed specimens.
478
RICHARD CLOUTIER AND PER ERIK AHLBERG
Barameda: Early Carboniferous rhizodont from Victoria, Australia. Skull roof, palate, and some postcranial elements preserved as natural molds.
Beelarongia: Late Devonian (Frasnian) canowindrid
osteolepiform from Victoria, Australia. Skull roof,
cheek, shoulder girdle, and pectoral fin preserved as natural molds.
Cheirolepis: Middle to Late Devonian (EifelianFrasnian) actinopterygian known from Scotland
and Québec. Represented by numerous complete, laterally compressed specimens.
Crassigyrinus: Early Carboniferous (ViséanSerpukhovian) tetrapod from Scotland. Largely
complete except for the tait.
Diabolepis: Early Devonian (Lochkovian) dipnoan
from Yunnan, China. Only the skull roof, palate,
and lower jaw have been described.
Diplocercides heiligenstockiensis: Late Devonian (Frasnian) actinistian from Bergisch-Gladbach, Germany. Skull roof, cheek, and part of the axial
skeleton are known.
Diplocercides kaeseri: Late Devonian (Frasnian) actinistian from Hessen, Germany. The neurocranium
has been described extensively.
Dipnorhynchus: a dipnoan. The best known species
is D. suessmilchii from the Lower Devonian (Emsian) of New South Wales, Australia. Skull roof,
braincase, palate, and lower jaw are known. Our
coding also includes data from D. kiandrensis and
D. kurikae.
Dipterus: Middle—Late Devonian (Eifelian—Frasnian)
dipnoan from Scotland and Germany, represented by numerous complete bodies.
Elpistostege: Late Devonian (Frasnian) elpistostegid
from Québec, Canada. Known from two incomplete skulls and a piece of vertebral column.
Eusthenopteron: widespread Late Devonian (FrasnianFamennian) tristichopterid osteolepiform. The coding is based on E. foordi from Québec, which is represented by numerous complete bodies.
Glyptolepis: Middle—Late Devonian (EifelianFrasnian) holoptychiid porolepiform from Europe
and Greenland. The whole body is known.
Gyroptychius: Middle Devonian (Eifelian—Givetian)
"osteolepid" osteolepiform from Europe and
Greenland. The whole body is known but only
the dermal bones have been fully described.
Holoptychius: Late Devonian (Frasnian—Famennian)
holoptychiid porolepiform of apparently worldwide distribution. Complete bodies, but endoskeleton rarely preserved.
Howqualepis: Late Devonian (Frasnian) actinopterygian from Victoria, Australia. Natural molds of
complete bodies.
Ichthyostega: Late Devonian (Famennian) tetrapod
from eastern Greenland. The dermal skull and
most of the postcranium are known.
Miguashaia: Late Devonian (Frasnian) actinistian
from Québec, Canada. Represented by complete
but crushed bodies.
Munia: Late Devonian (Frasnian) actinopterygian from
Gogo, Western Australia. Whole body known in
outstanding, three-dimensional detail.
Moythomasia: widespread Late Devonian (Frasnian)
actinopterygian. Scored on basis of Gogo material comparable to that of Mimia.
Onychodus: widespread Late Devonian (Frasnian)
onychodont. The best material comprises skull
bones and some postcranial elements from Gogo.
Osteolepis: Middle Devonian (Eifelian—Givetian) "osteolepid" osteolepiform from Scotland. Many
complete bodies, but Little information about the
internat skeleton.
Panderichthys: Late Devonian (Frasnian) elpistostegid
from Latvia and Russia. P. rhombolepis is represented by complete bodies from Lode, Latvia.
Polypterus: a primitive Recent actinopterygian from
equatorial Africa.
Porolepis: a "porolepid" porolepiform from the Lower
Devonian (Pragian—Emsian) of Europe and Spitsbergen. The dermal skull, shoulder girdle, scales,
and ethmosphenoid have been described.
Powichthys: porolepiform-like genus from the Lower
Devonian (Lochkovian) of Arctic Canada. Braincase and skull roof known. Associated lower
jaw, operculogular elements, and palatoquadrate
probably also belong to genus.
Speonesydrion: Early Devonian (Siegenian) dipnoan
from New South Wales, Australia. Only part of
the skull has been described.
Strepsodus: Carboniferous (Dinantian—Westphalian)
rhizodont from Europe and North America.
Known from one complete but poorly preserved
body and many isolated elements.
Strunius: a small onychodont from the Upper Devonian (Frasnian) of Germany and Latvia. Represented
by complete but rather poorly preserved bodies.
Uranolophus: Early Devonian (Pragian) dipnoan from
Wyoming. The skull roof, palate, lower jaw, and
postcranial dermal skeleton are known.
Ventastega: Late Devonian (Famennian) tetrapod
from Latvia. Lower jaw, palate, and cheekplate
are known; associated clavicles, interclavicles,
and ilia probably also belong to the genus.
Y oungolepis: sarcopterygian genus from the Lower
Devonian (Lochkovian) of Yunnan, China. Head
and shoulder girdle are known.
17. Interrelationships of Basal Sarcopterygians 479
Appendix 3: Data Set of 140 Characters for 28 Sarcopterygian Taxa
1111111111222222222233233333334444444444555555555566666666667
123456789012345678901234567890123456789012345678901234567890 1234567890
Acanthostega
Allenypterus
Barameda
Beelarongia
Cheirolepis
Crassigyrinus
Diabolepis
Diplocercides kaeseri
D. heiligenstockiensis
Dipnorhynchus
Dipterus
Elpistostege
Eusthenopteron
Glyptolepis
Gyroptychius
Holoptychius
Howqualepis
Ichthyostega
Miguashaia
Mirnia
Moythomasia
Onychodus
Osteolepis
Panderichthys
Polypterus
Porolepis
Powichthys
Speonesydrion
Strepsodus
Strunius
Uranoloplats
Ventastega
Y oungolepis
0LOL?000000111100101L0L1100110000101111LL101LL1110010101110111L0L1L1L0
OL1L000000000000011LL0000001200101011003? 1? 0010011011100110001L0L1L010
OL1L100000011100010??L00000110000110100201????0??001097997902929900010
1?010000??????0???001???0001?00001107002???10?0??001010??0?00999299"7
OLOL0100000000000P00000000010001000P0001L0L00000000010002?000000L0000?
OLOL0000000?11100101LLL1100110000100111LL101LL01?0010101110111L0L1L1L1
11 7?70001L00000011???0?? 0001712100?010771970111777799"979977999999990
OL I L0000000000000 1 1LL? 00000 1 200 10 10120020 1? 00 10011? 1 I 100110001L0L1L01?
OL1L0000000? 00000 I ILL?000001200101012002? 1? 0010? 11011100110001L0L1L0 I?
1? 0100L1 2L000701LL1LLL000011712000001003?11021207799777777777777777977
111L00011L000001LL1LLL000111112100001002?170212010010101110000211??01?
OL010000??0???100101L0001001100011011????101LL179097??9????????1001???
OL1L1000000101000100101000011000010010020101LL011001110110000021000011
OL 1 L0000001102000101 L000000100010111200211100101101101111010001101 L010
1L010000000101000100001000011000011010020101LLO??001010110000021000011
OL1L0000001102000101L000000120010111200211100101101101111010001101L010
OL00011000000000000001L00000L0000L000001L0L0000?0000000000000000L0000?
OL1L?000000111100101L0L1100110000101111LL101LL11?0010101110111LOL1LILO
OL1L000000000000011LL000000120010100100201?0010?10011100110001L0L1L01?
OL00011000000000000000L00000L0000L000001L0L000000000000000000000L00000
OL00011000000000000001L00000L0000L000000LOL000000000000000000000L00000
OL1L0000001100000100000000012001011110022100010?100101002L0001L1 OILO 1 L
1001000000010?000100101000011000011010020101LL01100101011000002100001?
OL010000000111100101L0001001100011001102010 ILLI I?001010111000021001011
OL00010000000000000LLLLO1000L0010LOOL000LOL001000LLOLOOLIL000ILOLI L010
11010000000102000101L0000001001100112002111001077011011110100011000010
1101000001?1010001???00000017010007010021110010779779999271000???00010
1?0?00012L000001LL???L00001??12000001097299929999999999?999000?11000??
OL1L10000001110001001? ???0011???0? 7?100??1?? 770?1079917777777L10? 701?
OL1L0000001?000001000000000? ?0010 1? 11002?17779991001?100??0001? 101LO I?
110100LIOL000001LLILLL00011??12100001003??102120?7"992999999021100010
OL? L700000011110010170????? 1??? 70?? 771??? I? IL? 11700??1011109999"99990
1101000001?1010011001070000770110?10100????0110??0???10?1070???1000010
11111111111111111111111111111111111111111
7777777778888888888999999999900000000001111111111222222222233333333334
1234567890123456789012345678901234567890 123456789012345678901234567890
A canthostega
1101L0?0000000?LL1100021010100??LL11097111701700211170111LLL0?71201011
0011010777111777797r>1017111?7001L111700111100?11?1???? 0001170011111100
Allenypterus
Baranzeda
101990?`1991?9299?9990097?991000110990?71??91110?2101110299992299?99029
?977779777197779777907979777777770199777777011072111077777771009 777979
Beelarongia
9 09 9 2L09 00000000?000 ?00000L000000000?0??L00? 0? L? 000000?? ? 0
Cheirolepis
909 909
1011?0??000?00OLL???002101099999LL99999112L01?002111??111LLLOLL??01001
Crassigyrinus
Diabolepis
00 I 00017010979999999102LLL?10?001099910197999997"99997797999999999997
Diplocercides kaeseri ?C010100001111111111101711117701011100011??010019777990729011117100
D. heiligenstockiensis 777171077711177"7771017111777077711700117701001??????0707770011117100
?101LOILL10000OLL?LL102LLL011L0010??1111099999999799999999799999772999
D ipnorhynchus
?101001LL10000OLL??L102LLL011L011011111101101101????1100010101010?0001
Dipterus
99797997220997999999099999999999299999977999979999999999999992797(i)100?
Elpistostege
1011000000111111011100210101000110110001110011002111000001001001111011
Eusthenopteron
0000100110111111011101210101001111110001111011010100110001110001010010
Glyptolepis
1011007700111111????002?0?01000110110001110019092999990901?7100110101?
Gyroptychius
000010011011111101??0121010100111111000111101100?1????0?0???00010"9"
Holoptychius
?0?000???00?0??0LO??00000100000000000000L000000??0??L00?0?L?0000099999
Howqualepis
110100?0000000ILL?770021010100??LL110?? 112L0110021117? 111LLLO77 1211011
lchthyostega
70970999991299927999101?11?990017011?00111?000119999920901??00010??100
Miguashaia
0000000000000000 LO 0000000000000000000000 LO 0000007000 LO 0000 L00000000000
Minda
0000000000000000L0000000000000000000000000000000?000L00000L00000000000
Moythornasia
LOL1000010111? 110?770121010?700110110?? 101100001011077070???7001107010
Onychodus
70?1?0007011111101??002?0??1000110110001110011009799990901?01001001010
Osteolepis
1011L000000?7?7??1??002101010001LL110001110011002117000? ILLL0001201001
Panderichthys
L010L00000000001L00100020001000110000000100010010000?00000L00001110?? 1
Polypterus
0000107110111111017101210101001110110001117011099999290209 777979" 9999
Porolepis
00?00010100111101?0001210101010110??000111999999999999979979999799 9999
Powichthys
7101001LL?000?OLL???102LLL?11L00929991110?9999999??9999799?99992999992
Speonesydrion
7977777779177777779909297779990192997999911111002111010?01070201199999
Strepsodus
7777777799129999999901?LLL??70011011700117700001?????? 07077700011???? 0
Strunius
L1OILO1LL10000?LL?7?102LLL??1L00101??111?1101100??????0?0???000?01?000
Uranolophus
11077099009779779999002201?100?999917991179790909999999177979999779999
Ventastega
00100011100000101100012101010100101101011??0?10?11999999?9999992?229"
Y oungolepis
Note. 0 = ples omorphic state; 1, 2, 3 = apomorphic states; ? = character not available; L = logical impossibility; P = polymorphic
states (0 and 1).