<oological Journal oJ lhe Linnean Sucrefy (1991), 102: 333-366. With 19 figures
A cladistic analysis of the cornutes (stem
chordates)
ANTHONY P. CRIPPS, F.L.S.
Notre Dame Senior School, Burwood House, Cobham, Surrey K T l l 1HA
Received Januacy 1990, accepted f o r publication Nowmber 1990
At the root of the calcichordate controversy is the problem of recognizing homologous similarity.
Only when a criterion or set of criteria for hypothesizing homologies is establishcd can the
calcichordate theory he tested against its main rival-the Stylophoran theory-by applying the
principle of parsimony. T h e criterion of topological similarity is applied to a three-taxon problem
involving a mitrate, the crown-group Echinodermata and the crown-group Chordata. T h e mitrate
shares more features with extant chordates than with extant echinoderms and the calcicliordate
theory is supported by a simple parsimony analysis. In a cladistic analysis of the cornutes, four
monophyletic families are recognized (Cothurnocystidae, Srotiaecystidae, Phyllocystidae and
Hanusiidae) and their interrelationships resolved using Hennig86 and the successive-weighting
procedure of Farris. Because the known fossil record of cornutes and mitrates is very poor, the
correlation between the cladogram produced for cornutes and their order of appearance in the
geological record is weak. All ofthe cornutc families must have originated in the Lower Cambrian at
the latest.
KEY WORDS:-Calcichordate
-
Stylophora
-
cladistic analysis - fossil record.
CONTENTS
Introduction .
. . . . . . .
Parsimony and the calcichordate controversy
T h e interrelationships of cornutes .
. .
. . . .
Phylogenetic analysis .
. . . .
Results of the analysis.
. . . .
Classification of cornutes .
. .
Derstler’s “advanced phyllocystids”.
. .
Calcichordates and the fossil record
.
.
.
.
.
.
.
Conclusions .
Acknowledgements
. . . . . .
. . . . . . . .
References
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
.
.
.
.
. . . .
.
.
.
.
.
.
.
.
.
.
.
333
336
345
354
354
359
360
361
364
364
364
IN‘I‘KODUCTION
T h e aims of this paper are to discuss parsimony analysis as a possible test of
the calcichordate theory and to present a cladistic analysis of the cornutes.
Cornutes are calcite-plated invertebrates found in the marine Palaeozoic
outcrops of Britain, Australia, Czechoslovakia, U.S.A., U.S.S.R., Morocco and
France. T h e group consists of approximately forty species, about a quarter of
which have been described in the past few years. Cornutes are closely related to
two other groups of Palaeozoic fossils-the solutes and the niitrates-which
also
+
002+4074/9 I /OLIO333 34 SOS.OO/O
333
0 1991 T h e Linnean Society of London
A. P. CRIPPS
334
have skeletons of calcite. These three groups are perhaps the most controversial
of all fossil taxa since specialists disagree on their orientation, the interpretation
of almost all parts of their anatomy and, consequently, their systematic position.
Until the 1930s cornutes and mitrates were generally held to be echinoderms
(Jaekel, 1900; Bather, 1900, 1913) and were grouped as the Carpoidea within
the phylum Echinodermata. An alternative view was briefly stated by the
Japanese zoologist Matsumoto: “The Carpoidea Jaekel . . . . . . may probably
stand at the base of the Chordata and be allied with the Urochorda in a certain
way” (Matsumoto, 1929: 27). This is the first statement (albeit vague) of what is
now called the calcichordate theory. T h e theory today is, in reality, a simple
systematic hypothesis: cornutes and mitrates, together with all of the known species of
solute, are more closeEy related to extant chordates than to extant echinoderms.
Matsumoto’s suggestion gained support from Gislin (1930), and over the last
20 years the calcichordate theory has been greatly elaborated by Jefferies (1967,
1968, 1973, 1984, 1986 and in press), Craske & Jefferies (1989), Jefferies &
Lewis (1978).Jefferies, Lewis & Donovan (1987) and Jefferies & Prokop (1972).
In addition to Jefferies’ coauthors, the calcichordate interpretation has received
support (either in part or in whole) from Eaton (1970), Bone (1972), Cripps
(1988, 1989a, 1990, in prep.), and Daley (in press).
The Stylophoran Theory is the main alternative to the calcichordate theory.
The exponents of this theory hold the view that stylophorans (cornutes, mitrates
and solutes) are stem-group echinoderms. Its supporters include Caster ( 1952,
1967), Chauvel (1941), Chauvel & Nion (1977), Regnault & Chauvel (1987),
Ubaghs (1978, 1981), Philip (1979), Derstler (1979), Sprinkle (1983) and
Parsley (1988). Of these authors, Derstler has been the most explicit on the
subject of Stylophoran systematics in providing a cladistic analysis of the group
and clearly stating his belief that the Stylophora is monophyletic (Derstler, 1979,
1982). Within the Stylophoran school there are two views on the nature of the
c r o w n chordates
m
.-mC
m
L
0
<
m
m
0
.-
C
3
I-
m
c
m
.C
2
0
Figure 1. Two X-trees showing the calcichordate and Stylophoran theories. A, ’The calcichordate
theory. T h e cornutes and mitrates are chordates and paraphyletic groups. T h e cornutes are all stem
chordates, the mitrates are crown chordates. B, ’l‘he Stylophora theory. T h e cornutes and rnitrates
are stem echinoderms. ‘Thr cornUtes are paraphyletic and the mitrates polyphyletic.
-
335
CORN LrTE SYSTEMATICS
hemichordates
Dexiothetica
m
m
E,
U
0
.-C
r
V
w
m
c
m
U
L
0
r
0
Figure 2. T h e interrelations of deuterostomes. T he lophophoratc phyla (Brachiopoda, Bryozoa aud
Phoronida) may not be deuterostomes s m J u i t r i c h and the relations between these three phyla
remain very uncertain. T h e hemichordates arc a pardphyletic assemblage, among which the
enteropneusts are most closely related to chordates a nd echinoderms than to either Cephalodisrus or
the colonial form Rhabdopleura. Dexiothetes sharr three dcrived characters-a
ralcite skeleton,
dexiothetism arid an internalized protosome which, within thc Chordata, are only present in fossil
forms (solutes, coriiutes and mitrates). Synapomorphy scheme: ( I ) trimerous body-plan; (21 radial
cleavage; ( 3 ) anus drvelops from the blastopore; ( 4 \ non-mosiac development; (5) pre-oral gut; ( 6 )
protosomal heart; ( 7 ) pharyngeal or huccol clefts; ( 8 1locomotory stalk; (9) loss of coloniality; (10)
distal sucker: ( 1 I)loss of right protocoel pore: ( 1 2 ) giant nerve cells; ( 13) enterucoelous corlom
formation; (14) tornaria larva; (15) calcite skeleton; (16) dexiothetism; ( 1 7 ) intrrnalization of the
protosome
appendage of cornutes and mitrates. Ubaghs (1961) has argued that it is a
feeding arm or aulacophore, whereas other Stylophora workers (e.g. Kolata &
Jollie, 1982) have argued a locomotory role for the appendage.
The calcichordate and Stylophoran theories can be represented by two
X-trees (Fig. 1 ) in which the short branches are fossil taxa. Exactly where the
Stylophoran school would place the solutes and the hemichordates is unclear
from their literature. In fact, there is no evidence that the hemichordates are a
monophyletic group (Cripps, 1990) and it is likely that the enteropneusts are
more closely related to chordates than to pterobranchs (Fig. 2 ) .
336
A. P. CRIPPS
A
B
Figure 3. The mitrate Mitrocystella inczpiens rniloni Barrande, Lower Ordovician. A, Dorsal surface. B,
Ventral surface.
PARSIMONY A N D THE CALCICHORDATE CONTROVERSY
The calcichordate theory is testable, contrary to the assertion of Thomson
(1987). The view of calcichordate workers that echinoderms and chordates are
sister-taxa (Fig. 2) and that, within the chordates, tunicates and craniates are
sister-taxa can be tested by molecular systematists and by cladistic analyses of
extant groups. These systematic hypotheses (Echinodermata Chorata and
Tunicata Craniata) have arisen from the study of fossil cornutes and mitrates
and hence demonstrate the potential of fossils to affect well-established views of
relationships based upon living groups (Hemichordata Chordata and
Acraniata Craniata).
A second test of the calcichordate theory involves the study of their calcite
skeletons, the detailed structure of which could reflect the nature of the
associated soft tissues as in living echinoderms. Studies of this type are only just
beginning but preserved calcite is, unfortunately, still a rarity among specimens
of cornutes and mitrates.
Patterson ( 1981: 2 16) suggested that the calcichordate theory could be tested
by parsimony analysis. A complete analysis would include all of the known
solutes, cornutes and mitrates as well as undisputed fossil echinoderms and the
extant chordate subphyla. However, it is possible to treat the calcichordate
controversy as a three-taxon problem and that is the approach adopted below.
The three taxa used are the crown group of the Echinodermata, the crown group
of the Chordata and the mitrate Mitrocystella incipiens Barrande (Fig. 3 ) .
The two crown groups are easily characterized (Table 1 ) and M . incipiens is an
abundant and well-preserved mitrate. The monophyly of the Chordata and of
the Echinodermata is well established, although see Lovtrup (1977) for an
alternative view on the Chordata. Use of a single species of mitrate avoids the
issue of whether the mitrates are monophyletic, paraphyletic or polyphyletic.
The differences between the calcichordate and Stylophoran schools can be
+
+
+
+
CORNU 1 t S\'SI'L1LlA7'ICS
337
TABLE
1. Synapomorphies of the crown-group Echinodermata and of the crown-group Chordata
Crown-group Echinodermata (aftrr Smith, I9841
[ 1 I Calcite skeleton of stereom
( 2 ) Development of right-hand side larval coelorns supprrssrd
( 3 ) Pmtanicral symmetry
Crown-group Chordata
( I I Post-anal tail with a notochord sand srgmrnred musculature
(21Bipartite brain (prosencephalon and deutrrc.nrrphal(,n)
( 3 ) Perforated ciliary-feeding pharynx with an ertdostylr
14) Dorsal nervr cord with paired nerves
( 5 ) Neural gland ? = Hatsrheck's pit ? = pituitary
Spinal ganglia are absent from tunicates and amphitrxus hut may h a w been secondarily lost if present in
corriutes and mitrates
outlined with reference to Table 1. Advocates of the Stylophoran theory
emphasize the fact that Mitrocystella incipiens shares with crown-group
echinoderms a skeleton of calcite. M.zncipiens does not exhibit pentameral
symmetry but, like all mitrates, has a bilaterally symmetrical outline. T h e
coelomic chambers of M . incipiens, their naming and interpretation, though not
necessarily their reconstruction, depend upon which group (chordates or
echinoderms) is chosen as closest extant relative. The shared character of a
calcitic skeleton is a sufficient reason for many workers to classify M . zncipzens as
an echinoderm. I know of no other possible synapomorphies of mitrates (or of
cornutes) and extent echinoderms, but the calcite skeleton remains the only
undisputed character in the calcichordate controversy.
Calcichordate workers believe that MitrocyJtella inc$iens shares with crowngroup chordates a post-anal segmented tail, branchial openings, a bipartite
brain and a dorsal nerve cord connected to spinal ganglia. A naive application
of the principle of parsimony shows that the calcite endoskeleton shared by
M . incipiens and echinoderms must he plesiomorphous and that the five
characters shared with extant chordates are synapomorphies. However, because
all of the chordate similarities of M. incipiens are disputed, this application of
parsimony fails to resolve the calcichordate controversy. Moreover, parsimony
cannot test the calcichordate theory unless these five characters, and hence the
calcichordate interpretation of the anatomy, are accepted! The problem
underlying the calcichordate controversy is, in my view, the recognition of
homologous similarity which will now be discussed.
Zoologists, before and after Darwin, have employed different criteria for
recognizing homology. Patterson (1982) suggested three criteria as tests of
homology: ( 1 ) similarity; (2) conjunction; and ( 3 ) congruence. The Gmilarity
test embraces topological, developmental and compositional similarity. The test
of conjunction can be stated as follows: if x and y occur together in the same
organism then x cannot be homologous with y. For example, the malleus of
mammals is generally believed to be the homologue of the quadrate of nonmammalian amniotes. If a species was discovered that had both a malleus and a
quadrate bone then the hypothesis of homology would be falsified. However,
there is a difficulty with this test which can be illustrated with a second example.
Another widely accepted homology is that of reptilian scales with avian feathers.
Despite the fact that many birds have scales upon their legs and feet in addition
338
A. P. CRIPPS
to having feathers, this hypothesis of homology remains generally accepted. I
conclude that the conjunction test cannot be applied without recourse to the
topological criterion of similarity.
The test of congruence is the test of parsimony. As Rieppel (1988) concluded,
this test must be subservient to the similarity test, especially to similarity of
topological relations, in order to avoid circular reasoning. If this test is used
without the similarity test, it is possible to erect and find corroboration for any
group of organisms.
I agree with Rieppel (1988: 60) that the first stage in character analysis is the
application of the similarity test. I n the case of fossils the developmental criterion
of homology is inapplicable and, in any case, there appear to be several
falsifications of this criterion. As one example, the adenohypophysis of myxinoids
and vertebrates (sensu Janvier, 1981) develops from endodermal or ectodermal
germ layers respectively, yet specialists on lower craniates d o not seem to doubt
their homology. Perhaps the detailed topological correspondence of the
adenohypophysis in all craniates is the reason why this homology is not seriously
questioned.
The use of the topological criterion of similarity, first proposed by Geoffroy
Saint-Hilaire (1830), is not without practical difficulties. Any comparison of the
topological relations of two structures requires a frame of reference. Yet an
important aspect of the calcichordate controversy is the disagreement over what
was the anterior and posterior surface of cornutes such as Cothurnocyslis elizae
Bather. T h e mitrates present an additional problem in this respect, for there is
disagreement concerning their dorsi-ventral orientation as well as over the
anterior and posterior surfaces. Any objective resolution of the calcichordate
problem appears to be thwarted. As fossils can only be interpreted in the light of
extant organisms it is common practice among palaeontologists to orientate
fossils in order to maximize similarity with living organisms. If it could be agreed
that crown chordates primitively consisted of a distinct head and tail, it would be
reasonable to orient cornutes in the same way, with the globular part (the head)
anterior to the long, thin part (the tail). Unfortunately, any consideration of the
distinctiveness of the head and tail in chordates leads into a debate of great
antiquity between segmentationists and anti-segmentationists. The latter school
sees a fundamental distinction between the chordate head and tail which is
perhaps best illustrated by Romer’s ‘somatico-visceral’ animal (Romer, 1972) as
the hypothetical ancestral vertebrate (Fig. 4). This animal would have
resembled a tunicate tadpole larva and a mitrate. Segmentationists regard the
vertebrate head as a segmented structure and deny any fundamental difference
from the tail. T h e ancestral vertebrate, in the opinion of the segmentationists,
Figure 4. Rorner’s “somatico-visceral animal”. An imaginary ancestral craniate with a distinct head
and tail like a rnitrate. After Romer (1972: fig. 8a).
COKKI:'I'E SYS'1l;MAI'ICS
339
would have been more similar to amphioxus than to the tadpole larva. So the
orientation of cornutes cannot be established through a comparison with the
primitive morphotype of crown chordates, about which there is no widespread
agreement. Fortunately, however, I believe that the orientation problem is
solved by another group of closely related fossils-the solutes.
If cornutes and mitrates are oriented according to the calcichordate
interpretation, then there is a strong case for believing that the large posterior
appendage is homologous with the tail of extant chordates. This would follow
from topological considerations and, as a hypothesis of homology, passes the tests
of conjunction and congruence (this is the case even if calcichordates are
considered echinoderms, since there is no known tail-less group more closely
related to extant chordates). The tail hypothesis can be contrasted with the
feeding-arm or aulacophore hypothesis of some Stylophora workers (e.g. Ubaghs
198 1 ) . This hypothesis involves a different orientation of cornutes and mitrates,
with the appendage at the anterior end of the animals. This is because the
mouth, the position of which determines the anterior end, would almost
certainly have been at the base of the aulacophore. Yet such a feeding arm could
not be homologous with the feeding arm of crinoids since the latter, according to
the cladistic analysis of Smith (1984), is an autapomorphy of the Crinoidea and
therefore a character acquired wilhin the echinoderm crown group. The question
of the function of the appendage can he divorced from any consideration of its
possible homology with the chordate tail, since it is widely accepted that
homologous structures can have different functions. The possibility remains that
the appendage could be the primitive homologue of a tail and yet function as a
feeding-arm. That the appendage was most likely a locomotory device is evident
from a comparison with solutes. T h e solutes possess a large posterior appendage
very similar to the cornute appendage (happily, all workers seem to agree on the
antero-posterior orientation of solutes). There seems no reason to doubt the
homology of these appendages, as the comparison in Fig. 5 shows. Yet, perhaps
realizing the danger to their own theory of accepting this homology, some
Stylophora workers have interpreted the obvious similarities as instances of
convergence (Caster, 1967). The solute appendage is claimed to be a locomotory
device, while the very similar cornute appendage is said to be a feeding arm!
Among Stylophora workers, Kolata & Jollie (1982) and more recently Parsley
(1988) accept that the cornute appendage was used for locomotion. I conclude
that the aulacophore hypothesis has been falsified and can only be protected by
ad hoc proposals of convergence. T h e most important contribution of solutes to
the calcichordate debate is that they allow us confidently to orient cornutes and
mitrates with the appendage at the posterior end of the head, unless one assumes
(without evidence) that the mouth has migrated from a more posterior position.
This result greatly strengthens the hypothesis that the large appendage was a
tail. Another consequence of the comparison with solutes is that Jefferies'
identification of the mouth in cornutes is most likely correct, as i t would occupy a
similar position at the anterior end of the head. If this opening is an anus, as
Stylophora workers believe, then it is necessary to propose that the mouth
migrated towards the posterior end of the animal or towards the anterior end if
cornutes retain the primitive position of the mouth. Moving the mouth entails a
reorganization of the internal anatomy which, although not impossible, seems
unnecessarily complicated in view of the absence of any supporting evidence.
340
A. P. CRIPPS
A
B
fore
mid
hind
Figure 5. A solute and a cornute drawn for comparison. A, The solute Dendrocystoides scotzcus
(Bather), Upper Ordovician (After Jefferies, in press). B, The cornute Gra~oqystirperneri, Middle
Cambrian. Not to same scale.
An internal structure at the base of the appendage adds further credence to its
interpretation as a tail. The structure in question sits in a calcitic basin and is
known from many natural internal moulds of solutes, cornutes and mitrates; the
calcite that once surrounded it has dissolved away. I t is always a bipartite
structure in mitrates and this is true for many cornutes as well. Situated on either
side of this structure are a number of rock-lumps, which in some of the bestpreserved specimens are connected to it by a slender bridge of rock. T h e rockbridges are oval or circular in cross-section. In mitrates a complex of canals exists
on both sides of the bipartite structure.
These canals were discovered by Chauvel ( 1941 : 160- 161 ) who considered
them to be channels for nerves; this interpretation has been accepted by workers
on both sides of the debate. T h e calcichordate interpretation of the structures
mentioned above is that the large bipartite structure was the brain, the rocklumps were ganglia and the rock-bridges and canals were nerves. This
interpretation provides a second synapomorphy of cornutes and mitrates with
extant chordates, in addition to the presence of a tail. Furthermore, it is a
relatively easy task to homologize the parts of the brain, the nerves and their
ganglia with those of craniates, using the topological criterion of similarity. For
34 I
COKNL. 1 :E SYSTEMATICS
mouth
bipartite
brain
dorsal nerve
cord
intestine
Figure 6. T h r tadpolr larva of
(.'ions
i n Irft lateral asprct. Aftcr M'illcy
j
18931.
example, the pyriform rock-lumps lateral to the deuterencephalon (posterior
division of the bipartite structure), sending two nerves (infilled canals) to the
dorsal surface of the head and two others forward to the mouth region, are
readily interpreted as trigeminal ganglia.
For Stylophora workers, the calcitic basin did not house a brain but was the
site of muscle insertion (Ubaghs, 1969: 31; Kolata & Jollie, 1982: 639). This
view, in my opinion, simply fails to interpret the complex of structures in this
region of the appendage. More importantly it appears dependent upon the
assumption that there is no connrction between the bipartite structure in the
midline and the complex of nerves either side ofit. That this assumption is false is
demonstrated by the numerous published photographs of this region. That such
an assumption is necessary is made obvious by any attempt to envisage a
bipartite block of muscle innervated by half-a-dozen surrounding ganglia and
with nerves connecting it to the surface of the head! There is certainly nothing
comparable in any living echinoderm or chordate.
Two criticisms are frequently directed at the interpretation by calcichordate
workers of the bipartite structure as a brain: ( 1 ) the 'brain' is too large for a
group of animals suggested to include the ancestors of extant chordates (e.g.
Bone, 1972: 12) and; (2) the 'brain' as reconstructed is posterior to the entire
alimentary tract, the heart, gonads etc.-such a bizarre morphology, i t has been
argued, is too incredible to be believed (Halstead: p. 206 in Jefferies, 1967). Both
points can be put into perspective through a comparison with the tunicate
tadpole larva (Fig. 6 ) . Using the larva of Ciona intestinalis as a n example, the
brain (which is bipartite) is almost twice the size of the brain of solutes, cornutes
and mitrates relative to the size of the head. T h e brain is also situated posterior
to the primordial pharynx and to a large part of the primordial gut. I conclude
that there is nothing exceptionally odd about the brain of calcichordates and no
reason to doubt its identification.
Another group of fossils also have a posterior appendage that might be
considered a tail. They are the cinctans (Fig. 7)-a small monophyletic group of
Middle Cambrian echinoderms. Their appendage, often called a stele, appears
to be an extension of the marginal frame of the head (Jefferies, in press). T h e
position of the appendage at the posterior end of the head suggests that i t is
homologous with the cornute tail and this hypothesis passes the tests of
conjunction and similarity. If the cinctan appendage is homologous with a tail
A. P. CRIPPS
342
A
B
Figure 7. T h e cinctan Trochovstztes bohemicus Barrande, Middle Cambrian. A, Dorsal surface. B,
Ventral surface. T h e posterior appendage exhibits no obvious internal or external segmentation.
and cinctans are echinoderms, then what has become of the tail as a chordate
au tapomorphy?
Applying the same criteria of homology discussed above, it is likely that the
chordate tail is homologous with the stalk of hemichordates, as originally
proposed by Eaton (1970). A tail may be distinguished from a stalk in having a
notochord and segmental musculature. Hemichordates have muscles in their
stalks but they are not segmented. T h e stalk also includes an extension of the
metacoels along its central axis, which could be a primitive homologue of the
notochord. I n fossil organisms it is impossible to say exactly when the notochord
arose, even if the functional anatomy of the tail is considered as explained below.
The notochord functions as an anti-compressional strut in living chordates, so
that tails can bend from side to side but cannot shorten or lengthen appreciably.
The hemichordate stalk is telescopic, therefore the coelomic extensions investing
it do not function in the same way as a notochord. Instead, when the stalk
contracts, coelomic fluid is pushed up into the head, causing it to swell. I n
cornutes, there is no compelling reason for reconstructing the tail with a
notochord in preference to coelomic extensions. An anti-compressional device
may have been desirable in the cornute fore tail as argued by Jefferies (1981,
1986) but coelomic fluid could perform the same job as the notochord if its
escape route to the head was cut off.
Features of the cornute tail absent from the cinctan stele are the presence of
large lumina between the dorsal plates and the internal and external
segmentation of the tail. By comparison with extant chordates, the lumina are
likely to have contained muscle blocks. Segmentation is a relatively easy
character to recognize in fossil material, as is the presence of lumina in the tail if
preservation is good. For this reason, these features provide a more practical
343
CORNU‘IE SYSTEMATICS
4
/
3
/
E
D
I
Q
Figure 8. T h e most parsimonious view of the early cvolution of the chordate tail. A, Hernirhordate
stalk. B, Cinctan stele. C , Solute tail. D, Coriiutc tail. E, Mitrate tail. Synapomorphies: ( I ! calcite
plating of stalk; ( 2 ) tripartite regionation, s e p e i i t a t i o n ; (3) stylocone, pairrd dorsal plates; (4)
styloid, paired ventral plates, dorsal ossirleb.
definition of a tail and allow it to be distinguished from both a stalk and a stele
(Fig. 8).
A third synapomorphy of Milroc_ystelln incipiens with extant chordates, proposed
by calcichordate workers, is the presence of multiple branchial openings. In fact,
the evidence for the existence of branchial clefts in mitrates, other than
Lagynocystis pyramidalis (Barrande), is very weak. In several species of cornutes
however, such as Colhurnocystis elitae Bather (Fig. 9), a curved row of gill slits is
present in the ventral integument. Multiple gills may be a primitive character if
the numerous gill clefts of enteropneust hemichordates are considered to be the
primitive condition. The recognition of pharyngeal clefts in cornutes is
dependent upon accurate restoration arid identification of the pharynx to begin
with. This inevitably involves a comparison with living organisms and therefore
a search among living groups for the best model. Jefferies maintains that the
reconstructed soft anatomy of cornutes and mitrates provides some of the most
powerful evidence in support of the calcichordate interpretation. Bauer ( 1989:
142) has suggested that reconstructing the soft anatomy on a chordate plan
appears “to presuppose the outcome of the phylogenetic analysis”. However,
reconstruction of the size and position of the chambers of the head is an objective
A. P. CRIPPS
344
A
n
B
n
-mFigure 9. T h e cornute Cothurnocystrs elizae Bather, Upper Ordovician. A, Dorsal surface. B, Ventral
surface.
exercise provided an important assumption is made. Calcichordate workers
deduce the positions of the head chambers in cornutes largely by studying
changes in stereom texture on the inner surfaces of the marginal plates. Smith
(1989) comments that there is no comparable change in stereom design in living
echinoderms and so the validity of this technique is, at present, difficult to assess.
Probably all workers would agree on two points: ( 1 ) that these reported changes
in stereom design exist and exhibit similar patterns in different species and; (2)
such changes in architecture are probably significant.
It is known that the detailed structure of stereom in living echinoderms almost
always reflects the nature of the associated soft tissue, whether ligaments, muscle
or nervous tissue. T h e assumption made by calcichordate workers is that the
changing designs on the inner surfaces of the marginals of cornutes are related to
the nature of the adjacent head chambers. If this assumption is permitted, then it
is possible to reconstruct the chambers of the head objectively. When this is
completed, the naming of these chambers requires the acceptance of a living
model. But Bauer is wrong to suppose that this involves a prejudgement of the
affinities of cornutes. As with any other character of these or any other fossils, the
next step is to compare the reconstructed chambers with those of living
organisms-living
echinoderms, living chordates and living hemichordates.
When this is done it is clear that cornutes resemble most closely the tunicates in
having, for example, a massive perforated chamber filling most of the head-the
pharynx. The mitrates exhibit many more detailed similarities with living
tunicates as is evident when their soft anatomy is reconstructed using similar
techniques. I conclude that the techniques used to reconstruct the soft anatomy
of cornutes are independent of the calcichordate theory, as is the recognition of
any similarity between the reconstructed chambers and those of living
organisms. However, the assumption on which those reconstructions depend
remains untested.
COKKL 1 L SYS I E:mmcs
345
Two further characters from the tail may also be shared with crown-group
chordates. These are a dorsal nerve cord and spinal ganglia, preserved a5 natural
internal moulds. The ganglia (rock-lumps) are thought to be sensory as they lie
outside of the structure interpreted as the nerve cord and because they were
probably intersegmental. It must be admitted that these synapomorphies are
dependent upon acceptance of the tail hypothesis which, in my view, can be
strongly argued. However, alternative interpretations of the internal moulds are
possible if the ‘tail’ is in fact an aulacophore (Ubaghs, 1981)-a viewpoint
rejected above. T h e presence of spinal ganglia may also be questioned as a
potential synapomorphy with crown chordates because neural crest (and
therefore its derivatives, including spinal ganglia) is not present in acraniates or
tunicates.
I n my view, strict application of the topological criterion of homology to the
calcichordate problem, leads to the following conclusion. The mitrate
Mitrocystella incipzens shares with living chordates a segmented tail, a bipartite
brain, a dorsal nerve cord and, possibly, spinal ganglia. Mitrocystella inc$iens
shares with living echinoderms a calcite skeleton. T h e principle of parsimony can
now be employed and the Stylophoran theory is rejected. As might be expected
from this conclusion, the addition of other mitrates to the character analysis adds
further possible characters to strengthen the calcichordate theory iJefferies,
1973, 1986; Jefferies & Lewis, 1978) but brings no new potential
synapomorphies with the crown group of the Echinodermata. I have considered
here only one way of testing the calcichordate theory. Other ways, especially the
results of molecular systematists, may reinforce or contradict the theory. In
particular, sequence data are needed for hemichordates so that Jefferies’
Dexiothetica (Echinodermata Chordata) can be tested against the more
traditional grouping of Hemichordata Chordata.
+
+
‘ I N E 1NI’EKK E L~A.1I O N S H 1 PS OF CORN L’J’ES
For the reasons argued above, cornutes are considered stem chordates in the
present work. The choice of suitable outgroups for the following analysis is, as
always, dependent upon the acceptance of a more inclusive phylogeny. In the
case of cornutes, two suitable groups are the solutes and the mitrates. The
mitrates (Fig. 8) are a paraphyletic group belonging to the crown group of the
Chordata. Members of the mitrate grade may be distinguished from cornutes by
the features listed in Table 2. The solutes may also be a grade group, as some of
them appear to be more closely related to cornutes than to each other (Jefferies,
in press). However, a cladistic analysis of solutes has yet to be attempted and the
possibility of a monophyletic Soluta unexplored (possible group autapomorphies
include a feeding-arm, the so-called sugar loaf plate and a hook-shaped end to
the tail). It was Jefferies’ placing of some of the solutes in the Chordata (as a
more primitive grade of stem chordates than the cornutes) that prompted the
present analysis. I have previously attempted a cladistic analysis of the cornutes
(Cripps, 1988) using only the mitrates as an outgroup and, since they are crown
chordates, I used them to determine the derived character-states. A consequence
of this procedure is that it denied n priori the possibility of cornute monophyIy
and it also proved impossible to compare many cornute features, such as the
branchial skeleton, with those of mitrates. The second problem was
A. P. CRIPPS
346
TABLE
2. Characteristic features of t h e m i t r a t e g r a d e of calcichordates
( I ) Right pharynx with right branchial openings
( 2 ) Three-layered ventral skeleton
( 3 ) Plates d and i make rontact upon the dorsal surface of the head
(4) Absence of a ventral strut
(5) Absence of a separate plate k
(6) Internal branchial openings and left and right atrial chambers
(7) Absence of the cornute mid and hind tail
(8) Ventral surface of the head convex
(9) Expansion of the marginal plates across the dorsal surface of the head
(10) Gonorectal canal opens into the hranchial region
( I 1 ) Absence of major dorsal fore-tail plates
(12) T h e first pair of fore-tail plates of cornutes from part of the head-skeleton in mitrates (plates epsilon and
theta)
Characters 6 1 2 appear partly or fully developed in the most crownward known cornute Prokopzrystis mergli
Cripps (1989a)
circumvented by using a cornute, Ceratocystis perneri Jaekel, to root the tree.
Ceratocystis perneri is the only cornute to retain a hydropore and, mainly on this
basis, is usually considered the most primitive member of the group.
In the present analysis I use solutes and mitrates to determine character
polarity as shown in Table 3. The solutes, as primitive stem chordates, are used
to root the tree. Permitting some of the character-states in mitrates to be
plesiomorphic allows the possibility of a monophyletic Cornuta, a possible
outcome denied in previous analyses of the group by calcichordate workers.
Additionally, since the analysis of Cripps (1988), several new species have been
described some of whose characters seem to contradict previous groupings. For
the solutes, I adopt the dorso-ventral orientation of Kolata et ul. (1977) which is
also adopted by Jefferies (in press). As previously mentioned, some of the solutes
are more cornute-like than others. Three genera have been chosen to form the
outgroupSyringocrinus, Belemnocystites and Iowacystis-all
of which have a
distinct marginal frame like cornutes. lowacystis sugittaria Thomas & Ladd is
shown in Fig. 10 and its marginal plates named after their probable homologues
in cornutes. It is worth pointing out that the vast majority of the character-states
in the data matrix (Table 4) do not depend upon correct identification of the
homologues of cornute marginal plates in solutes. For example, the absence of a
c-appendage from solutes is certain, whether or not the identification of plate c in
1. sugittaria is correct. For the mitrates I have chosen the three most primitive
species, which are the basal species of the three chordata subphyla. These are
Chinianocarpos thorali Ubaghs (Craniata), Peltocystis cornuta Thoral (Tunicata) and
Lagynocystis pyramidalis Barrande (Acraniata). I use the ‘convex-surface-down’
TABLE3.
Polarity-decision t a b l e
for a c h a r a c t e r , X, w i t h t w o
states-Xl
Solutes
Mitrates
Derived state
in cornutes
and
X2
XI
XI
XI
X,
X,
xz
x, xz
XI x*
X,
X,
CORSU'l't: SYSIEMA'I'ICS
6
347
g-ar m
Figure 10. T h e solute Iou~aysttssagittaria I'hornas and Ladd, Upper Ordovician. A, Dorsal surface.
B, Ventral surface.
orientation of this group, so that the convex surface of the mitrate head is
homologous with the ventral surface of the cornute head (see Cripps, 1989a). In
the analysis below, I have used 34 species of cornute and 75 characters. All of the
cornutes have been described with three exceptions: Prochauvelicystis semispinosa
(Daley, in press), Procothurnocystis oixensi (Woods & Jefferies, in prep.) and Beryllia
miranda (Cripps, in prep.). Milonic_ystis kerfornei Chauvel was identified as a
mitrate by Chauvel (1986) but is a phyllocystid cornute, as shown by Cripps (in
prep.). Most of the characters used in this study can be conveniently grouped for
the purposes of discussion. A more detailed discussion of the following characters
will be found in Cripps (in prep.): 6, 16, 17, 35, 39, 56, 58, 67, 73-75.
( 1 ) Head openings (characters 1-8)
T h e openings of the cornute head can be identified using two approaches: (a)
topological comparisons with hemichordates, solutes and extant chordates; and
( b ) functional considerations. Jefferies (1986) gives the most complete account of
the evidence. Four of the characters in this category concern the position of the
gonopore-anus. Jefferies has argued that, in solutes, the gonopore was situated at
the anterior end of the head near the mouth and to the right of the midline
(Jefferies, in press). The position of the gonopore in cornutes is variable
(characters 2-5) though it is always confluent with the opening of the rectum
and is at the posterior end of the head. All situations of the gonopore-anus in
cornutes are considered apomorphic compared with solutes and in all except one
or two species, it is located to the left of the midline. T h e mouth in solutes is at
the base of the feeding-arm, which is either ventral or terminal. In cornutes, the
mouth is either dorsal or terminal. When terminal it is either a wide slit-like
opening or a small opening at the tip of an oral cone. Neither condition is found
in any solute. The number of branchial openings in cornutes is highly variable
( 3 or 4-c. 50). Jefferies has identified a single branchial slit in the solute
A. P. CRIPPS
348
TABLE
4. Character data matrix for 34 species of cornutes (stem chordates). Character states are
the derived conditions (? = missing data, N = not applicable)
a,
d
e
1
y3
-3
m
- c J J
m
1
a,
0
5
.3
-c
a,
It
.3
1
0
Q
SOLUTES
Ceratocvstis perneri
Cera tocvstis vizca inoi
Nevedaecvsti s americana
Protocvsti tes menevensis
Co thurnocvst is primaeb-a
Cothurnocxstis elirap
Co thurnocvst is f e 1 1 inensis
Cothurnocvst is courtt~.ssolei
Cot hurnoc.vsti s bi f ida
Proco thurnocvst is owensi
Ph.vlIocvstis blavaci
Phvl Iorvstis ci.assimarqinara
Phvl 1ocvst is sa la iri ca
Prochacrvel icvs t is semispiriosa
Chauvelicvstis spinosa
Chauvel i cvs t is ube qhhs i
Chauvel icvst is vizcainoi
Mi lonicvst i s kerfornei
h,v@delo theca m i f f ei
Ce 11iaec.vst is 1 i.cni eres1
Proffel
lieecvstis ubeghsl
Thorelicystis relchiori
Thorelicvstis zegoraensis
Thorelicystis griffei
Bohmieec.vstis bouceki
Scotiaecystis collepsa
Scotiaecys tis curve te
Hanusia prilepensis
Henusie obtusa
Hanusia sarkensis
Beryllie riranda
Donfrontia pissotensis
ReticulocPrpos hanusi
Prokopicystis rerffli
tfITRATES
e
1
u
~ O O O O O O O O O O O N O O O ~ N O O ~ N
O O O O O l O O O l O l l O O O O N l O l O O O l O l l 2 O O O l
N
? ? ? ? ? ? ? 0 1 0 0 1 ? 0 0 0 0 ~ 1 0 1 0 0 0 1 0 1 ? 1 0 0 0 ?
? ? ? ? ? ? ? 0 1 1 0 1 1 1 1 0 0 0 1 0 1 0 0 0 ? ? 7 1 2 0 0 1 1
l
1
1
1
l
?
1
1
O
7
0
0
1
1
1
1
1
?
1
I
1
1
?
?
1
1
1
7
1
1
?
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
l
l
1
7
7
7
1
1
1
?
1
1
1
7
?
1
1
1
l
l
7
7
1
1
1
?
1
?
7
1
1
7
7
?
0
0
0
?
0
0
O
7
7
7
0
0
O
O
O
7
0
0
?
?
0
0
0
?
0
0
?
0
O
7
?
7
0
0
1
?
1
1
O
7
7
7
0
0
l
l
l
?
1
1
?
?
0
0
0
?
0
?
0
0
O
?
?
7
1
1
0
?
0
0
1
7
7
7
1
1
O
O
O O O O l O l l O O O O N l O l O O O l O l l 2 O O ; l
0 0 7 ? 7 ? 1 1 1 1 0 0 0 1 0 1 0 0 0 1 1 1 0 2 0 0 l 0
0 0 1 1 1 0 1 2 1 1 0 0 0 1 0 1 0 2 1 1 2 1 0 3 0 0 l l ~
7 7 0 1 1 0 1 2 1 1 0 0 0 1 0 1 0 0 1 1 ? 1 0 2 0 0 l 0
0 0 ? ? ? ? 1 ? 1 1 0 0 0 1 0 1 0 1 1 1 0 1 0 3 0 0 1 0
? 7 ? 1 1 0 1 1 1 1 0 0 0 ? 0 1 0 1 0 1 0 1 0 3 0 1 ! 0
0 0 0 1 1 0 1 1 1 1 0 0 0 1 0 1 0 1 1 1 7 1 0 2 0 0 i 0
0 1 0 1 1 0 1 1 1 1 0 0 0 1 1 0 ~ N 0 0 N 0 1 0 2 1 1 0
0 1 0 1 1 O 1 1 1 1 0 0 0 1 1 O Y N l O N O l O 2 l l ~
0 1 ? ? ? ? 1 ? 1 1 0 0 ? ? ? O N N ? O N 0 7 0 2 1 ? 0
0 0 7 1 1 0 1 1 1 1 0 0 0 0 0 1 0 0 0 1 0 1 0 1 0 0 1 0
O 0 0 1 1 0 1 ? 1 1 0 0 0 0 0 O N ~ O O N O O l O l l O
0 0 0 1 1 0 1 1 1 1 0 0 0 0 0 1 0 0 0 0 N 0 0 2 0 1 ~ 0
? 0 0 1 1 0 1 1 1 1 0 0 0 9 0 1 0 0 0 0 N 0 0 3 0 1 1 0
O 1 O O O O 1 1 1 1 O 1 1 O O O N N O O N O O Z l O l O
? ? ? 7 7 ? ? ? 1 1 0 1 1 0 0 O N N O O N O O l l l l O
7 7 0 0 0 0 1 0 1 1 0 1 0 1 1 O N N 0 ? ? ~ 1 . 3 0 1 1 0
? 0 0 0 0 0 1 1 1 1 0 1 0 1 0 1 0 0 0 ? 7 ? 1 3 0 1 1 0
0 0 l l 1 0 1 2 1 1 0 0 0 l 0 1 0 0 0 1 0 1 1 3 0 1 1 0
0 0 1 0 0 1 1 2 1 1 0 0 0 0 0 1 0 7 0 1 0 ? 7 3 0 0 1 0
0 1 1 0 0 1 1 2 1 1 0 0 0 1 0 1 0 7 0 1 7 1 0 3 0 0 1 0
0 1 1 0 0 1 1 1 1 1 0 0 0 0 0 1 0 ? 0 1 ? ? 0 2 0 1 1 0
0 1 1 0 0 1 1 2 1 1 0 0 0 1 0 1 0 2 0 1 2 0 0 3 0 0 1 0
0 1 1 0 0 1 1 2 1 1 0 0 0 1 0 1 0 2 0 1 2 0 0 3 0 0 1 0
1 O O O O O 1 1 1 1 O 1 O 1 O l l O O O N O l l O O l O
7 0 0 0 0 0 7 7 1 1 0 1 0 1 0 1 1 0 0 7 7 7 1 1 0 0 1 0
7 0 0 0 0 0 ? ? 1 1 0 1 0 7 7 1 7 7 0 7 ? 7 1 1 0 1 1 0
1 0 0 0 0 0 1 1 1 1 0 1 0 0 0 O N N O O N O O O O 1 1 0
1 0 0 0 0 0 1 0 1 0 1 1 0 0 0 0 N N 0 0 N 0 0 0 0 0 1 0
1 0 0 0 0 0 1 0 1 0 1 1 0 0 0 0 N N 0 0 N 0 0 0 0 1 1 0
l O O O O O l O l O l O O O O O N N O O N O O O O O O O
l O O O O O O N O O O O O O O O N N O O N O O O O O O O
~
~
N
349
C O R K I T E SYS'I'EMATICS
o o o o
I) o N o o o o o o o 0 o o o o o o o o o o o o o 0 0 0 o 1) o
1 0 0 0 0 i 1 it 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 . 0 0 0 0 (1
o o n
n 1 1
o II (I
0 I) 0 0 0
I)
1 0 o 0 0 1 1 0 0 0 0 0 0 ? 0 0 0 0 0 0 0 0 0 0 0 0 o 0 0 0 0 0 f l 0 ? 1 1 0 0 0 0 0
o o n o o i i
o
~
o
o
~
~
~
~
o
o
~
~
o
o
o
o o oo n oo n ~
o
o
o
~
~
0 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 l ~ 1 0 0 l J 0 0
o o o o o 7 ? ? o o o ? o o o o o I o o o o o o o o ? o n n o II 11 I 1 1 ) n o o o n
n
o o o o o ~ ~ o o ~ o i o o o o o o n o o o o o o o o o o o o oi oo oo n~ o o o
o o o o l l l o o l o o o o o o o o l o o o o o o o o o o l l l ~ l'
I ~ ' ? ! I l I I O f l O f l
0 1 0 0 0 1 1 ? 0 1 0 ? 0 9 0 0 0 0 1 0 0 0 0 0 0 0 ? ? 0 0 I l O O O I l 0 ~ O
0 0 ? ? ? 1 1 0 0 0 0 0 1 1 1 0 0 0 0 0 0 0 0 0 0 0 ? 0 1 ' ~ 0 ~ 1 0 l fl l 1i l ~r
0 0 0 0 1 1 1 0 0 1 0 1 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 9 1) 0 n 0 1 I 0 0 0
o o o o o I 1 o o I o o I o o I 1 o o o 1 o o o o o 1 o n
o I n .I I I ) n n o
o
n
o
o
O f l O
, 1 0 0
0 0 0
o
I.
r,
o o o o ~ ~ o o ~ o o i o o i i o o o i o o o o o i o o n o ~ o o ~ o o o o o n ~
o o o
1:
o o
?
o o I 1 o o o o o o o o o
? 7
o
? 7
o
:I
o
.I
o o ? o i i ? o i o o ~ i o o o o o o o o o o o o ~ l o ~ u o
~ o o o i ? ? o i i o i i o o Io ~O O O O O ~ O I ~ o ?i
0 0 0 0 0 1 7 ? 0 1 1 0 1
o o o o o 1 : o o 1 1 o 1
0 0 0 1 O l ? ? 0 1 0 0 1
0 0 0 1 0 1 7 ? ? 1 0 7 1
1 0 0 0 0 1 0 0 0 0 O ? 1 1 1 0 I 0 i
1 0 0 0 0 7 o o o o o o 1 1 1 o L r) I
1 0 0 0 0 0 0 0 0 0 0 0 0 0 ? 0 0 0 1
1 0 0 0 0 0 0 0 0 1 0 7 0 7 1 0n o 1
7 11 n n o r i : n
o o oI o1 o0 0 1 l o o
o~ n ? I I ~ I I 0 0 3
0 0 I 1 0 I 1 0 I) 0
I I O ? I n I I 0 0 0
0 0 7 n o n o 0 0 0
0 0 ? 1 0 0 0 0 0 ' :
o n
o o o o o i ~ ~ o o o i 1 1 o o o o o o o o o o ? o o i o o 1 n o o ~ 1 o o o o ~ ~ o
O O O O O l l O l o O l l l l o O O O O o o o o 7 o o l o ~ l l o o o 71 n o o o o 0
0 0 0 0 0 1 1 0 0 0 0 ? 1 0 1 0 0 0 0 0 0 0 0 0 0 0 ? 1 1 0 v 0 0 0 1 1 0 l 1 0 0 0 0
o o o o o I ? ? o o 0 7 7 7 I o o o o o o o o o o 0 7 I 1 1 1 n o II n 1 1 o o o o ? 0
a o o o o ~ i o o o o i i o i o o o o o o o o o o o o i ~ ~ ~ ~ o u i ~ ~ o o o o ~
0 0 0 0 0 ? ? 7 0 0 0 7 1 1 1 0 0 0 ? 0 0 0 0 0 ? 0 ? 1 0 n 0 0 0 0 0 0 0
~ o ~ o o ~ i o o o o i ~ ~ ~ ~ o o o o o o o o o o o ~ ~ o n o o i i o o o o o o
o o i o o ~ i o o o o ~ ~ ~ i ~ o o o o o o o o o o o i i ~ o o o i ~ o n o o o o o
1 0 0 0 0 1 1 7 1 0 0 1 1 1 0 0 0 0 0 1 0 1 0 0 1 0 0 1 0 0 l 0 1 0 0 l 0 0 0 0 0 0
1 0 0 0 0 7 : 7 0 0 0 ? 1 1 0 0 0 ? 0 1 0 1 0 0 ? 7 0 1 ~ ~ 1 0 ? ? ? ? o o o 0 ? n
1 0 0 0 0 ? ? 7 1 0 0 7 1 1 0 0 0 0 0 1 0 1 0 0 ? ? 0 1 0 0 ? ? 0 1 0 0 1 0 ~ 0 ? 1 0 0 0 0 ? 0
o 1 o o o 1 1 1 o o o o i i o o i o o o 1 ~ 1 0 o o ? 1 o v 0 f ~ 1 o o ~ n n o i o o
o 1 o o o i 1 i o o o 1 i i o o i o o o o o 1 1 1 o o i o o o o i n o 1 o o o ~ ~ o
o i o o o ~ ~ i i o o i ~ i o o o o o o i o ~ o o o o i o n o ~ ~ ~ n ~ ~ o o o l o
0 1 0 0 0 1 1 1 1 0 0 1 1 1 0 0 0 0 0 0 7 0 0 1 1 0 0 7 0 0 0 0 1 0 0 1 0 0 0 1 1 1
0 0 0 0 0 0 N 0 7 0 0 1 1 1 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 ~ 1 0 0 1 0 0 l 0 0 0 1 1 1
A. P. CRIPPS
350
0
1
2
Figurc 1 1 . Variation in the shape of the stylocone among cornutes. A, Reticulocarpos hnnusi. B,
Cerutocyslis uzzcninoz. C, Thohordiqds grzyez. Stylocone shape is treated as an unordered character in
this analysis.
Dendrocystoides scoticus (Bather), located at the left posterolateral corner of the
head. The increased number of openings in cornutes may have reflected a
changing role for these openings, from outlet valves for excess water to filterfeeding, since cornutes (unlike solutes) have no feeding arm. Among those
cornutes for which the number of branchial openings is known, several species
have nine or fewer openings. The next highest number is about 14 in
C o ~ h ~ r n o ~elizae.
s t i ~ I take the large number of openings in C. elizae and in the
scotiaecystids to be the derived condition among cornutes.
( 2 ) Branchial skeleton (characters 9- 1 1 )
The single branchial slit in Dendrocystoides scoticus is surrounded by a n area of
small plates (Jefferies, in press). In cornutes, three kinds of specialized plates are
sometimes associated with the branchial openings: (a) anterior u-plates; (b)
posterior u-plates; and (c) interbranchial elements. The u-plates surround the
openings, whereas the interbranchial elements are situated between the openings. To anticipate the results of the cladistic analysis in this paper, the
interbranchial elements most likely evolved from the u-shaped plates within the
family Scotiaecystidae. T h e so-called ‘pores suturaux’, described by Ubaghs in
Phylloystis crassimarginata Thoral (Ubaghs, 1969: 27, 28) may be surrounded by a
fourth type of branchial skeleton. In the specimens of P. crassimarginata I have
observed, the plates surrounding the openings do not appear to be significantly
different from the u-shaped plates of other phyllocystids and are almost certainly
homologous. Several species of cornute lack any specialized branchial skeleton.
(3) Stylocone (characters 12, 13)
The Stylocone is a relatively massive ventral element in the mid tail of all
cornutes in which the tail is preserved. It always has an anterior excavated area
and a median longitudinal groove upon its dorsal surface. No such structure
exists in any known solute, although some of the large mid-tail elements of
certain solutes may be primitive homologues of the cornute stylocone. If the
convex-surface-down orientation of mitrates is correct, the dorsal styloid of
mitrates cannot be the homologue of the cornute stylocone unless a n ad hoc
hypothesis of mid-tail rotation is introduced.
T h e stylocone in cornutes varies in outline shape, from a parallel-sided
structure to a funnel-shaped structure (Fig. 1 1 ) .
CORNU'I E SYS'I'EMAI'ICS
35 1
E
0
1
2
Figure 12. Character-coding for the relative sizes of the appendages in rornutcs. A-C, hAppendage. A, C'era/ocystzsp c m e n . B , Co!hurnocv.rtzs prlrnneon. C, S r o l i a e y l i s collapm. D-F, (-Appendage.
D , Thoralirvstis rnrlrhior?. E , Procothurnocys/i.i u u w , i . F, .Cco/iarcyslis curaala.
(4)Ventral strut (characters 14-18)
A strut, variable in its shape and composition, strengthens the ventral
integument of most cornutes. Its posterior part is always an extension of plate g,
but anteriorly it may be continuous with the anterior marginal frame or
terminate short of the frame. 'The strut is usually composed of two plates
(extensions of plates g and a ) but sometimes an additional strut-plate is present
(plate rn or z ) . One objective of this study is to determine, through the test of
congruence, whether the extra strut-plate is homologous in all cornutes which
have it.
( 5 ) Spikes and appendages (characters 19-28)
Spikes are here defined as extensions of the ventral or ventrolateral surfaces of
the marginal plates terminating in a point. Appendages are anteriorly directed
extensions of the marginals which nearly always have a rounded tip. Entire
marginal plates may be modified as appendages. Solutes have neither spikes nor
appendages (except for the feeding arm). Marginal plates which sometimes have
spikes are plates f , k , I , t and e. Plates often modified as, or having, appendages
are b, c and 1. The length of an appendage is considered in relation to the size of
the head (Fig. 12). In Hanusza spp. the /-appendage is ribbed upon its ventral
surface and, in place of spikes, plates,fand k have low keels which I assume are
homologous with spikes.
(6) Shape of lhe head (characters 29-31)
T h e head varies in shape from bilaterally symmetrical in outline to bootshaped, sometimes with a very pronounced 'toe' (Fig. 13). There are two sorts of
352
A. P. CRIPPS
0
1
2
3
Figure 13.Coding for the degree of asymmetry exhibited by the cornute head (the relative size of the
‘toe’ region), A, Be$ia miranda. B , Hanusia prilepensi~.C, Prolocysliles meneuenis. D, Cothurnocystis elizae.
symmetrical outline: (a) heart-shaped (cordiform) symmetry with well
developed posterior lobes to the head and a closed frame (see below); and (b)
elongate symmetry with a relatively narrow head and an open frame. Elongate
symmetry is shared by some cornutes with the mitrates and the three cornutelike solutes used to root this analysis. While many solutes have an asymmetrical
head, the three cornute-like species tend towards symmetry.
( 7 ) Integuments (characters 32-38)
Of the three solutes constituting the outgroup, two-Ioowacystis saggituria and
Syringocrinus sincluiri Parsley & Caster-have a flexible ventral integument and I
take this to be the primitive condition for cornutes. The dorsal surface of all three
solutes has fewer, larger plates that do not form an integument.
The integument plates of most cornutes are constructed from fine-grained
labyrinthic stereom, but in some species retiform stereom forms two-dimensional
plates. In at least two species-Progalliaecystis ubughsi (Ubaghs) and Galliaecystis
lignieresi Ubaghs-retiform stereom has been iaid down as a superficial veneer
covering the labyrinthic stereom.
The three species of the genus Hunusiu have relatively large integument plates,
especially upon the dorsal surface of the head. One very large
plate-LDIP-situated
in the ‘toe’ region of the head, can be readily
homologized in all three species (Cripps, 1989b). A large integument plate
occupies a roughly similar position on the dorsal surface of Ceratocystis perneri
(Plate CPL, Jefferies, 1969) and Ceratocystis vizcainoi Ubaghs.
The keel plates (kpines of Ubaghs, 1969) are elongate integument plates with
a pointed anterior end and a broader, blunt posterior end. Found only in two
species-Procolhurnoystis owensi and Cothurnocystis fellinensis Ubaghs-the Cpines
may be homologues of the left keel of the triradiate ridge found in some other
cornutes such as Cerutocystis perneri.
(8) Hind tail (characters 39-41)
The hind tail of solutes consists of a series of unpaired dorsal elements, each of
which contacts a single large ossicle ventrally. The paired dorsal hind-tail plates
of cornutes are symmetrically arranged in all species except for Protocystites
meneuensis Hicks. The length of the hind tail, when known, varies considerably
CKIRNLU'E SYSI'EMA'I'1C:S
353
among cornutes (cf. for example 56 segments in Cothurnocystis elizae with three
segments in Prokopiystis mergli Cripps). T h e solute hind tail is very long in all
described species and this is probably the primitive condition for cornutes. Four
species of cornute have a very short hind tail (fewer than five segments):
Domfrontia pissotensis (Chauvel), Beryllia miranda, Reticulocarpos hanusi Jefferies &
Prokop and Prokopic_ystis mergli. In these species the tail, though short, is relatively
massive compared with the size of the head as if to compensate. It is possible
that, in some cases, part of the hind tail has not been preserved thereby giving a
false impression of the true length of the tail. When only a single specimen of a
species is known (e.g. Hanusia spp.) then the length of the tail, as preserved,
cannot be assumed to be the true length. When more than one specimen is
known, each with the same number of hind-tail segments, the probability that
the true length of the tail is preserved increases dramatically.
(9) Plater of the marginal frame (characters 42-67)
Marginal plates are named using the alphabet notation of Jefferies 8r Prokop
(1972). Plates given the same latter in different species are considered
homologous.
The dorsal bar, present in some cornutes, is formed from inward extensions of
marginal plates a and d. Whether a homologue of the bar was present in the first
mitrate is doubtful since, of the three primitive mitrates, only Pellocystis cornuta
has an a-d contact. The polarity of this character may also be questioned since
an a-d contact exists in Iowncysti.5 Jagzftaria. However, the 'dorsal bar' in
I. sagittaria does not separate two areas of integument and no a-d contact exists
in Belemnocystites. T h e presence of a dorsal bar is probably therefore a derived
character among cornutes.
The validity of some of the characters of the marginal frame is dependent
upon correct identification of the homologues of the cornute marginals in solutes.
Yet if, for example, the plate identified as I in lowaystis (Fig. 10) was in reality a
primitive homologue of plate s, the use of plate s as a character could still be
justified by emphasizing its shape. In all cornutes with a plate s, this plate is
elongate and convex inwards in dorsal aspect. If plate s is indeed a primitive
character, present in solutes, an elongate plate s, convex inwards, is the derived
state.
Similarly, plate x cannot, with certainty, be considered absent from solutes,
but a n L-shaped plate x definitely is.
Plates u and w are two smail plates situated on the ventral surface of some
cornutes, between a and d. I have identified possible homologues of these small
plates in lowaystis sagittaria (Fig. 10B). ( A pair of similar plates is also present in
Belemnocystites wetherbyi Miller & Gurley .) In two cornute species- Thora1irysti.c
melchiori (Ubaghs) and Thoralicystis grtfei (Ubaghs)-a single plate occupies the
position of u and w. Whether this plate is ZI, w or a fused u-w is unknown, but
there is no reason to suspect that i t is non-homologous with either plate.
( 10) Characters 68-75
Most of the remaining characters require no further comment. The marginal
frame of cornutes may be described as either 'open' or 'closed'. A closed frame is
one in which the outer edge of the integuments is completely bounded by calcite
(e.g. Fig. 12f). In an open frame, thc anterior end of the integuments is
A. P. CRIPPS
354
unbounded in the region of the mouth. An open frame is always associated with
a terminal mouth. The three solutes constituting the outgroup all have a closed
frame.
Five species of cornute are much smaller than all other species (see table in
Cripps, in prep.) and, in this respect, are similar to the most primitive mitrates
which are much smaller than all other mitrates. Solutes are, in general, much
larger animals than cornutes or mitrates.
VTIL and VTIR are the most anterior pair of ventral fore-tail plates in
cornutes. Cripps (1989a) argued that these plates are homologous with plates
epsilon and theta of the mitrate head.
Phylogenetic anaEyszs
All data were analysed using Hennig86, version 1.5, by James S. Farris.
Solutes were specified as the outgroup. The majority of characters are binary
characters and entered as either 0 (plesiomorphic) or 1 (apomorphic). Missing
data and data ‘not applicable’ to particular taxa are entered as question marks.
Multi-state characters (13, 23, 26, 29, 30) were treated as non-additive
(unordered) using the ccode-option. No differential weights were applied. The
most parsimonious tree or trees were calculated using the mhennig, bb and ie
commands. The results were as follows:
mhennig-found two trees @ 193 steps, consistency index = 0.41
bb-found 68 trees (@ 188 steps, consistency index = 0.43
ie-abandoned after 72 hrs of searching without a solution.
I n view of the size of the matrix and the low consistency index of the most
parsimonious trees found by the mhennig and bb commands, it is not surprising
that the more powerful ie command failed to find the shortest tree(s) in a
reasonable period of time.
From the 68 trees found using the bb command, a Nelson consensus tree was
produced (Fig. 14). The first of the 68 trees was then subjected to the successive
weighting procedure of Farris (1969). This approach assigns a greater weight to
congruent characters and is therefore an a posteriori weighting routine. It resulted
in six equally parsimonious trees of 520 steps with a consistency index of 0.70.
One of the six trees, containing two trichotomies, is shown in Fig. 15.
Two less parsimonious solutions of particular interest were analysed using the
tree editor (Dos Equis). The results of the bb analysis, before and after successive
weighting, were edited and the lengths of the new trees recorded:
Monophyletic cornuta
Juxtaposition of the
Scotiaecystidae and the
Phyllocys tidae
bb ( 188)
194
Successive weighing (520)
590
194
524
Resulh of the analysis
Throughout the following discussion I use the scion concept of Craske &
Jefferies ( 1989).
I
outgroup
Ceratocystis perneri
Cerat o cystis vizc ainoi
Protocystites menevensis
Prochauvellcystis semispinose
Amygdalotheca griffei
Milonicystis kerfornei
-
Chauvelicystis spinosa
Chauvelicystis vizcainoi
L
Chauvelicystis ubaghsl
Phyllocystis salairica
-
Phyllocystis crasslmarginata
Phyllocystls blayaci
Galllaccystis lignieresl
Progalliaecystis ubaghsi
I
-
Hanusla sarkensis
-
-
Hanusia obtUSa
Hanusia prilepensls
I
outgroup
Ceratocystls perneri
Ceratocystts vlzcafnol
-
I
Protocystites menevensis
N e v a d a e c y st i s a m e r i c a n a
dL
,r
Colhurnocystis primaeva
C o t h u r n o c y st l s f e l l i n e n s i s
-
5l
Procothurnocystis owens/
Cothurnocystls courtessolei
Cothurnocystis elizae
Cothurnocystis blfida
I
L
Thorallcystis melchlori
Thorallcystis zagoraensis
7
Thoralicysrls
grlffel
Scotlaecystls colfapsa
Scotiaecystis curvata
Amygdalotheca grlffel
Milo n l c ys t l s k e rf one I
-r
phyllocystls salairica
Phyllocystis blayaci
Phyllocystis crasslmarglnata
a1
I
+
Prochauvelicystls semisplnosa
Ch s u v e l i c y st i s s p l n o s a
Cheuvelicystls ubaghsl
Ch a u v el i c y st i s v i z c slnol
Galllaecystis lignlerasl
I
Progalliaacystis ubaghsl
-
Hanusla prllepensls
Hanusla sarkensls
Hanusla o b t u s a
Reticulocarpos hanusl
Beryllla mlranda
E
DomflOntfE plssotensls
r
Prokoplcystls mergll
rnitrates
SddIHI3 'd 'V
9SE
C:ORNL''l'K S Y S ' l ' ~ h l A ' 1 ~ l C ~ S
3.57
The Nelson consensus tree in Fig. 14 contains two trichotomies and two
polytomies (one consisting of 12 and another consisting of five unresolved nodes).
Previously recognized monophyletic groups such as the Phyllocystidar and the
Scotiaecystidae are not present. A classification based on any consensus tree,
especially one with so many multiple furcations, will inevitably be highly
unstable. I have therefore based the classification below upon the cladogram
resulting from the successive weighting procedure (Fig. 15). While the
justification of Farris's successive weighting technique remains debatable, the
results are reasonably close to expectations as judged from previous analyses
(Cripps, 1988 (using PAUP); Jefferies, 1986; Daley, in press).
A comparison with the results obtained by Cripps (1988) using PAUP reveals
that the three families which resulted from this earlier analysis
(Cothurnocystidae, Scotiaecystidae and Phyllocystidae) remain intact and are
strengthened in the present work. Furthermore, the interrelationships of these
families to each other and to the mitrates remains unchanged (Fig. 16). An
additional group, which I have named the Hanusiidae, has emerged but Hanusia
spp. were only recently described. 'The position of the Phyllocystidae, crownward
of the scotiaecystids, has been reinforced. Amygdalotheca grzfei Ubaghs, for a long
time considered a close relative of the mitrates, is a phyllocystid (Clripps, in
prep.). The systematic position of Hanusia in Fig. 16 differs from Cripps ( 1989b)
in which this genus was thought to be more crownward than Galliaerys~isand
Figure 1.5. Cladogram resulting from thr siiccessi\e weighting procedure of Fari-ib's f 1969,
synapomorphy scheme: ( I ) rigid head floor; (2,./-and k-spikes; (31 asymmetrical Iirad: 14-1 open
frame; (5)triradiate ridge on dorsal surface of head; (6) hind tail with paired dorsal platrs; 1 7 1
h-appendage; (8) c-appendage; ( 9 ) styloconr; (10) I-appendage; ( I 1 ) e-spike; I 12) dit-like lermrnal
moulh: ( I 3 ) LDIP; ( 14) absence of hydroporc; [ I 5 ! flexible hcad roof: (16) gonopore-,inus situ,ited t ( i
left oftail; (17) posterior u-platrs; (18) oral cone; (19) ventral strut (contacting anterior iiamt.): 120)
anterior u-plates; ( 2 1 ) L-shaped plate r; (22) /iruh/r headfloor; (23) absence o f triradiate ritlgc ( o r
transformation into keel plates); (24) Plate t; (251 /-spike; (26) kecl plates; (27)long Gappendage;
(28) large number of branchial openings; (29) absence of keel plates; (30) enlarged toe
region; ( 3 1 ) absence of18 or U J (or fusion); (32)enlarged toe region; (33) right side of hcad convex
rightwards; (34) absence of x; (35) plate r; (361 lcft side of head formed largcly from plate k ; (37)
funncl-shaped styloconr; (38) absence of y; (39) large number of branchial openings; (40)
absence of i-k contact, (41) interbranchial elrinrnts: (42) righ/ rnar,girt t f h r a d ? / r a q h f ;(43)dorsal
mouth; (44) gonorectal canal opens into branchial region; (45) absence of v and w; 146)
absence of c; ( 4 7 ) ilosedframe; (48) plate r ; (49)long I-appendage; (50) long b-appendage; 151 i
bobbin-shaped dorsal integument plates; (52) cihwirr 0f.f and k-spikes: (53) absence of v and m;
(54) anterior strut plate; (55) ahsenre uf r-k coritnc/; (56) ahserrce (fr-appmdagr; 157) a h w t c e 111
b-appendage; (58) absenrr oJ I-appendage; (59)plate t; (601 gonorertal canal opens abo\r thr lire tail;
(61) ahJeircu o f t o e region; ( 6 2 ) margirials with a dorsal ridge; (63) cordiform head; ( 6 4 ) t d l > [ r u t ridge; (65) dorsal integument plates with wi-tical proresses; (66) platrs h. z iind .I' limn ail invcrtrd
U-shape: (67) dorsal mouth; (68) c l o d frame; (69'1 cordiform symmetry; 1 7 0 1/-spike: 1 7 1
plate h-c; (721 spines attached t~ right sidr of head: 1 7 3 1L-shaped platc /; (74)L-shaped plate x;
(75) spines attached to left and right sides ofhrad; I 761 b- arid /-branches o f plate a meet a t a n acute
angle; 1771 expanded plate h; (78) ahsenre o/-plate.v; ( 7 9 ) absrncr nj'branchial skuleton: (80)nbwnr-r 111 ( i n
oral rnne: (81) slit-like terminal mouth; (821 parallel-sided stylocone: ( R 3 j ,f- and k-k
plate a with long facet for contacting anterior strut plate; (85)dorsal bar; (86)I-appendage; 1871
i-apprndage with ribs: (88) LDIP; (89)dccply rxcavatrd marginal platrs; (901 plates a and I with a
dorsal keel; ( 9 1 ) rhorl shut; ( 9 2 ) absenre u/ /or rrgiori: (931 head with a periphcrdl llaiigr; ,94!
dwarfism; (95) short hind tail: (96) 2-D retikirm intrgument platcs: (97) short, forward curving
plate k; 198) optic embayments: ( 9 9 ) rzgh/ margin uf head slraigh/: [ 100) dorsally cxpandrd ni.irginal
plates; I 101 ) expanded plates h and z; [ 1021absenvc of major dorsal fore-tail plates; (10.7) rt,zid head
rooj; 1104) V T I L and V T l R contact platr> h and 1; (105) gonorectal canal opens into the
branchial region. Clharacters in bold arr parallrllisms, italicized charactcrs arc r n w d s .
Characters I 7 and 54 are possibir parallellisins. C:li;ii-;icters 23 and 34 are possiible rrvcrs;ils.
~
358
A. P. CRIPPS
0)
m
m
I
0
.-U
n
in
2.
0
0
1
C
2Ul
c
I
c
3
0
L
I)
m
I
in
2,
0
m
.-m
I
0
0
0
0
v)
m
U
.a
2,
I
0
-0
2,
Az
P
m
m
E
.in
3
C
m
I
-
in
m
m
.-
I
L
E
Figure 16. The relationships of thr four cornute families to each other and to the mitrates and solutes
(outgroup).
Progalliaecystis. The outline-shape of Hanusia was considered transitional between
the boot-shaped head of primitive cornutes and the symmetrical outline of the
most crownward species of cornutes, the mitrates and extant chordates. The
single autapomorphy given by Cripps (1989b: 238) for the scion of Hanusia is the
division of the brain into a n anterior prosencephalon and posterior
deuterencephalon. This character is now known to have a wide distribution
among cornutes and is most probably plesiomorphic. One of the autapomorphies
of the family Hanusiidae is the presence of a long anterior strut-plate which
makes contact with the 6-branch of plate a. If Hunusia is more crownward than
Galliaecystis and Progalliaecystis this unusual form of the strut can be interpreted as
the primitive homologue of the type of short strut characteristic of the scion of
(Reticulocarpos hanusi+ Beryllia miranda). I n my view, whether the smaller ‘toe’
region of the head of Hanusia is an autapomorphy of the genus or is a step
towards outline symmetry remains uncertain.
Three particular consequences of this analysis with regard to plate
homologies, and therefore plate nomenclature, are considered below.
( 1 ) Plate t . Possession of plate t (that is, a plate situated between plates k and
I) characterizes the Cothurnocystidae and also the Phyllocystidae. T h e nonhomology of this plate in these two groups emerged from the results of a PAUP
analysis (Cripps, 1988) and is here reaffirmed. The differences in form of plate t
between the cothurnocystids and the phyllocystids may now be considered
significant. In the cothurnocystids t is a relatively long plate with a welldeveloped spike. I n the phyllocystids t is primitively short and never has a spike.
Such differences would not normally be thought important unless non-homology
is indicated by parsimony analysis.
CORNU'I'E SYS'I'EMATICS
359
( 2 ) Anterior strut-plate. Ten species of cornute have an anterior strut-plate,
including the hanusiids, most of the mitrate-like cornutes (Beryllia, Domfrontia,
Reticulocarpos) and two of the phyllocystids (Milonicystis and Amygdalotheca grzfei) .
It is equally parsimonious to consider the anterior strut-like homologous in all
these species or, alternatively, that the extra strut-plate was evolved twice and
lost once. T h e former hypothesis is preferred as it seems heuristically more useful
to view similarity as a product of inheritance rather than of convergent
evolution. I n a previous paper (Cripps, in press) I called the anterior strut-plate
of the phyllocystid Milonicystis kerfornei plate z to distinguish it from the anterior
strut-plate (plate m ) of mitrate-like cornutes which I thought was probably not
homologous. However, the abandonment of either rn or z is probably premature
unless future analyses support the present conclusion.
( 3 ) Platey. Platey is a small plate situated immediately anterior to the tailinsertion upon the dorsal surface of the head. In the cladogram in Fig. 15, this
plate has a curious distribution. I n evolutionary terms, y is lost on two separate
occasions (once within the Scotiaecystidae and once by the scion of Hanusia) and
reacquired by Beryllia miranda. As with plate t therefore, plate y should probably
be renamed to reflect this conclusion (perhaps in B. miranda).
Two character transformations, considered probable by calcichordate
workers, are tested in this analysis.
( 1 ) U-plates > interbranchial elements. T h e hypothesis that the u-shaped
plates surrounding the branchial openings evolved into the interbranchial
elements of some scotiaecystids is in accord with the results presented here. If the
transformation did take place then it would have occurred between the latest
common ancestors of the parascion of Thoralicystis melchiori and the parascion of
Thoralicystis zagoraensis Chauvel.
( 2 ) Triradiate ridge > keel plates. Jefferies'
view
(personal
communication) is that the keel plates of Procothurnocystis owensi and Cothurnocystis
fellinensis are remnants of the left keel line of the most primitive cornutes such as
Protocystites menevensis. This transformation is neither supported nor denied in the
present analysis. T h e most parsimonious solution depends on whether or not this
homology is specified at the start of the analysis.
CLASSIFICAI'ION O F CORNUTES
The following classification is based upon the cladogram in Fig. 15 and uses
the sequencing convention of Nelson (1972). I have made no attempt to
construct subordinate classifications within monophyletic plesions such as the
Cothurnocystidae and all species within such groups are sequenced.
Phylum Chordata
Plesion (Genus) Ceratocystis
Ceratocystis perneri Jaekel
Ceratocystis vizcainoi Ubaghs
Plesion Protocystites menevensis Hicks
Plesion Nevadaecystis americana Ubaghs
Plesion Cothurnocystis primaeva Thoral, sedis mutabilis
Plesion (family) Cothurnocystidae, sedis mutabilis
Cothurnocystisfellinensis U baghs
360
A. P. CRIPPS
Procothurnocystis owensi Woods and Jefferies (in prep.)
Cothurnocystis courtessolei U baghs
Cothurnocystis elizae Bather
Plesion (family) Scotiaecystidae
Cothurnocystis bijida Ubaghs
Thoralicystis melchiori (Ubaghs)
Thoralicystis zagoraensis (Chauvel)
Thoralicystis grzffei (Ubaghs)
Bohemiaecystis bouceki Caster
Scotiaecystis curvata Bather
Scotiaecystis collapsa Cripps
Plesion (family) Phyllocystidae
Unnamed taxon 1
Amygdalotheca grzffei Ubaghs
Milonicystis kefornei Chauvel (Cripps, in prep.)
Unnamed taxon 2
Unnamed taxon 2a
Phyllocystis salairica Dubatolova
Phyllocystis blayaci Thoral
Phyllocystis crassimarginata Thoral
Unnamed taxon 2b
Prochauvelicystis sernispinosa Daley (in press)
Chauvelicystis spinosa U baghs
Chauvelicystis ubaghsi (Chauvel)
Chauvelicystis vizcainoi ( Ubaghs)
Plesion (family) Hanusiidae fam. nov.
Galliaecystis lignieresi Ubaghs
Progalliaecystis ubaghsi ( Ubaghs)
Hanusia obtusa Cripps, sedis mutabilis
Hanusia sarkensis Cripps, sedis mutabilis
Hanusia prilepensis Cripps, sedis mutabilis
Plesion Unnamed taxon
Beryllia miranda Cripps (in press)
Reticulocarpos hanusi Jefferies & Prokop
Plesion Domfrontia pissotensis (Chauvel) (Cripps, in prep.)
Plesion Prokopicystis mergli Cripps
Su bph yl um Cephalochord a ta
Subphylum Tunicata
Subphylum Craniata
DERS‘I’LER’S “ADVANCED PHYLLOCYSTIDS”
In his 1979 paper, Derstler presented a cladistic analysis of cornutes and
mitrates in which the latter group emerged as a polyphyletic assemblage. In
Derstler’s scheme, the mitrates evolved from two (possibly three) groups of
cornutes. One of these ancestral groups of cornutes is called by him the
“advanced phyllocystids” or the Amygdalothecidae. Included in this family are
three species: Galliaecystis lignieresi, Amygdalotheca grzfei and Reticulocarpus hanusi.
The family is characterized by two features: ( 1 ) a free zygal plate and (2) fused
CORN U'1'1: SYS'I'EMAl'ICS
36 I
right and median adorals. The zygal is termed the anterior sturt plate ( m , z ) by
calcichordate workers and has been discussed above. This plate is not free in
A. grzfei in that it is sutured to the marginal frame anteriorly. An anterior strut
plate is also present in Lfomfrontin pissotensis, Berytlia miranda, Progaltiaecystis
ubaghsi, Milonicyslis kerfrnei and all species of the genus Hanusia. As shown in the
present work and by Cripps (in prep.), A . griefei is not closely related to R. hanusi
or to other mitrate-like cornutes but is a phyllocystid.
T h e right and median adoral plates are plates h a n d y . The process of fusion
cannot be directly observed in the fossil record but may be inferred from a wellcorroborated cladogram. A separate plate y is absent not only from Derstler's
Amygdalothecidae but also from most of the scotiaecystids.
I find that there are no characters supporting a monophyletic
Amygdalothecidae but that several characters presented here show that some
members of this group are more closely related to mitrates than to each other.
There is good reason to believe that all mitrates share a unique common ancestor
(Table 2 ) , despite the different views on mitrate orientation and disputed
reconstructions of mitrate soft anatomy. T h e transition from the cornute to the
mitrate grade has been explored in a series of papers by calcichordate workers
(Jefferies & Prokop, 1972; Cripps, 1989a,b, in prep.). Most of the mitrates can
be assigned to the three extant chordate subphyla (Jefferies, 1973, 1986; Jefferies
& Lewis, 1978) and therefore they form a paraphyletic group within the
chordate crown group.
CALCICHORDAI LS AND T H E FOSSIL RECORD
In Fig. 1 7 the geological ages of the 34 species of cornutes studied in this
analysis are plotted, as are the appearances of the mitrates and non-mitrate
craniates. From left to right, the plesions are plotted in order of their increasing
relationships to the mitrates and the chordate crown group. In my view, a plot of
this kind serves only to indicate the quality of the fossil record. In other words,
the stratigraphic record is interpreted in the light of comparative anatomy, not
vice-versa (Nelson, 1978). It follows that the fossil record (specifically the order
of appearance of species) cannot falsify a systematic hypothesis based upon
comparative anatomical studies. T h e data given for the first appearance of nonmitrate craniates in the Lower Cambrian is based upon the view that some or all
of the conodonts are best interpreted as craniates. Nevertheless, the conodonts
remain a controversial assemblage and if they are not stem craniates (some of
them, for instance, may be chaetognaths (Szaniawski, 1987)) then the earliest
craniates-heterostracansare
found in the Upper Cambrian and Lower
Ordovician. The mitrates appear in the Tremadoc and survive into the
Carboniferous but most mitrates probably belong to a single large monophyletic
plesion of stem craniates (Jefferies, in prep). Figure 17 suggests that all of the
cornute families arose in the Lower Cambrian at the latest. An evolutionary
radiation of the group followed, dominated by variations in feeding and
locomotion strategies. T h e geological record of cornutes (and of mitrates) is
extremely poor as judged from Fig. 17 and from the fact that, although known
from all continents except Antarctica, fewer than 90 species of calcichordates
have been discovered. Of this number, the vast majority come from just three
countries-France.
Czechoslovakia and the U.K. T h e cornutes were most
o
Lowe r
Middle
uppe r
'remadoi
3
1
1
Figure 17. The stratigraphic occurrence of the 34 species of cornutes, arranged, from left to right, in order of their increasing relationship to the mitrates and non-mitrate
craniates. Taxon names are constructed from the first two letters of the genus and species name, the only exception being Protocystites meneuensis which is PRMN (to distinguish
this species from Prokopzcystis rnergli).
l
Arenig
Llanvirn
-1andeilc
Caradoc
Ashgill
w
N
Q1
CORNU'I'E SYSI'EMA'I'ICS
363
14
12
n
al
'G
10
al
P
a,
-
0
0
I-
m
0
E
6
D
2
4
2
MC
UC
T
AR
LV
LD
C
AG
B
430
448
458
0.3
488
478
488
505
0.2
525
0.1
540
1
580
580
540
520
500
480
1
I
460
440
Myr
Figure 19. Rates of morphological evolution in the cornute family Scotiaecystidae. A, Cladogram of
the scotiaecystids in which the nodes separating the three species of Th-horulicyslis are collapsed to
reflect their contemporaneity. These species arc treated as a single taxon for the purpose of
calculating the rate of evolution. T h e numbers associated with the internodes are determined from
Fig. 15 and are thc number of character-statr changes between two successive cladogenic events.
The origin of a pair of sister taxa is taken as 5 Myr hefore the earliest occurrence of the oldrr sister.
For explanation of taxon names see Fig. 17. B, Ploc of the rates of change, calculated by dividing the
number of state changes along an internode by the age difference of the two cladngrnic cvents it
separates. Horizontal bars represent the average rate of morphological evolution. T h r greatest rate
of change (0.3 state changes/million years) coincides with the period of greatest specific diversity,
whirh is during the Arenig.
364
A. P. CRIPPS
diverse during the Arenig (Fig. 18) which was also a time of rapid morphological
evolution in the cornute family Scotiaecystidae (Fig. 19).
CONCLUSIONS
Resolution of the three-taxon statement involving Mitrocystella incipiens, crown
group chordates and crown group echinoderms requires the acceptance of a
criterion for homology recognition. Application of the topological criterion of
homology leads to the conclusion that M . incipiens is most closely related to
crown chordates and is, therefore, a stem chordate. A cladistic analysis of
cornutes using Hennig86 and the successive weighting procedure of Farris results
in a paraphyletic group with some cornutes more closely related to mitrates than
are others. Within the assemblage of cornutes four monophyletic families are
recognized-Cothurnocystidae, Phyllocystidae, Scotiaecystidae and Hanusiidae.
The systematic position of Cothurnocystis primaeva is uncertain. T h e fossil record of
cornutes is judged to be very poor on two grounds: ( 1 ) a poor fit of the times of
appearance of the species with the nodes of the cladogram and; (2) the relatively
small number of species known for a group with global distribution.
ACKNOWLEDGEMENTS
Dr R . P. S. Jefferies and Dr A. B. Smith kindly read and made critical
comments on an earlier draft of this paper. This work was supported by a grant
from the Central Research Fund of London University which enabled the
author to study fossil material in France and in the U.S.A.
REFERENCES
BATHER, F. H., 1900. Chapters 8-12. In E. R . Lankester, A Treatise on zoology. Part III. Echinoderma: 1-216.
London.
BATHER, F. H., 1913. Caradocian cystidea from Girvan. Transactions of' the Royal Suciety of Edinburgh, 49:
359-529.
BAUER, A. M., 1989. Review of the ancestry of the vertebrates. Journal of Geological Education, 37: 142-143.
BONE, Q., 1972. The Origin of Chordates. Oxford Biology Readers 18. Oxford University Press.
CASI'ER, K . E., 1967. Contributions on pp. S550, S561-4. In R. C. Moore (Ed.), 7reatise on lnverkbrate
Paleontology. Par1 S. Echinodermata 1 ( 2 / .
CHAUVEL, J., 1941. Recherches sur Ies cystoides et Ies carpoidcs armoricains. Me'moires de la .Socit!tP Giologique
el Mine'ralogique de Bretagne. 286 pp, 7 PIS.
CHAUVEL, J., 1986. M i h i c y s l t S kerfornei n. gem n. sp. un nouvel echinoderme homalozoaire de I'Ordovicien
armorician. Hercynica, I I ( I J : 79-81.
CHAUVEL, J . & NION. J., 1977. Echinodermes (Homalozoa: Cornuta et Mitrata) nouveaux pour
I'Ordovicien du .Massif Armorician ct consiqurnces paliogiographiques. Gdobios, 10: 3 5 4 9 .
CRASKE, A. J. & JEFFERIES, R. P. S., 1989. A new mitrate from the Upper Ordobician of Norway and a
new approach to subdividing a plesion. Palaeontology, 321 I ) : 69-99.
CRIPPS, A. P., 1988. A new species of stem-group chordate From thc Upper Ordovician of Northern Ireland.
Palaeontology. 3 l ( 4 / : 1053-1077.
CRIPPS, A. P., 1989a. A new stem-group chordate (Cornuta) from the Llandeilo of Czechoslovakia and the
cornute-mitrate transition. zoological Journal of the Linnean Society. 96: 49-85.
CRIPPS, A. P., 1989h. A new genus of stem chordate (Cornuta) from the Lower and Middle Ordovician of
Czechoslovakia and the origin of bilateral symmetry in the Chordates. Geobios, 22(2): 215-245.
CRIPPS, A. P., 1990. A new stem craniiite from the Ordovician of Morocco and the searrh for thc sister-group
of the Craniata. zoological Journal o/ the Linnean Socieb, 100: 27-7 1.
CKIPPS, A. P., in prep. Two cornute speries from the Ordovician of Normandy and a reinterpretation of
Milonzqystzs kerfornei.
C:ORNtI'I'E SYSI'EM241'IC:S
365
DALEY, P. E. J., in press. Two new stem chordates iCornuta) from the Lowrr Ordo\ician of Shropshire
(U.K ) and Southern France. Palaeontolqey.
DERSTLER, K., 1979. Biogeography of thc stylophoran rarpoids (Echinodermatai. In J . (;ray & A. J .
Boucot (Eds), Hisloricnl Biogeography, Plate TrrloniiJ and /he Chan~qin~qEnriironmmt: 9 I - 104. Orrgon State
University Press.
DERSTLER, K., 1982. Estimating the rate o f m o r p h o l o ~ i r a lchange in fossil groups. In B. Marnet & M . J .
Copeland [ Eds). Proceedings of /hr 7hird .Vui/h .Imericon Paleon/olo,@a/ C ~ I Y ' R / ~ OL~dnrnr
~.
I : 131-136
Montreal.
EATON, T. H., 1970. T h e stem-tail problem and the ancestry of chordates. Jourtinl ofPa/mn/olngv. 44: 969-979.
FARRIS. J. S.. 1969. A successive approximati(ins apprciach to character weighting. .$w/rmn/n ;nologv. 18:
374-385.
G E O F F R O Y SAINT-HILAIRE, E., 1830. Printiprv dr Philosophie <oologrque, disrules en M a r s 1830. nu Spin de
1';lctldamie Royale des Sciences. Paris: Pichon et Ilider.
GISLEN, 'I., 1930. Affinities hetwern the Echinodrrmata, Entrropneusta and Chordonia. Coulopska Brdra,?
,fi& Lppsala. 12: 199-304.
JAEKEL, O., 1900. i'ber Carpoidecn: cine n e w Klassr von Pelmatozoen. <ei/Jthr(/i der Deiit\fhrn (;eo/ogi,\rhen
Gesellschaf/, 52: 661-677.
JANVIER, P., 1981. 'I'he phylogeny of the Craniata. with particular reference to the ,ignific;incc of fossil
'agnathans'. Journal qf Vertebrate Paleoniologv. 1: I 2 I 159.
JEFFERIES, R. P. S., 1967. Some fossil chordates with cchinodcrm affinities. .('ympo!in o / / h e ;oo/ocrI.al So+y
sf'
Lonmdon, 20: 163-208.
JEE'E'ERIES, R. P. S., 1968. 'rhe subphylum Calcichordata (Jrfferies 19671 primitkt hssil c.hordatcs with
rchinodrrm affinities. Ridletin of /he British .\friswm (.V-a/uralHistory), Geology Serirs, 16: 243 339.
ERIES, R . P. S., 1969. O'eratoys/zs pcrnvri rl Middle Cambrian chordate with w h i n o d r r n ~affinitirs.
Palneontology, 12: 49G.535.
kpramzda1t.r (Barrandr! and thr ancestry of
JEFFERIES, R . P. S., 1973. T h e Ordovician Cossil Lagvno&i
amphioxus. Philosophical Transadions of the Koval .Socrr!y. ( B ) . 265: 409-469.
JEFFERIES, R. P. S.. 1981. I n defence of thr calrirhordatrs. zoological Journal qf'the Linnenn , S o t l e ! ~o/L ondon,
~
73: 351-396.
JEFFERIES, R. P. S., 1984. Locomotion. rhapr, ornament and extrmal ontogeny i n some mitrate
calcichordates. ,7ournal oJ Vertebrate Paleontologv. 4: 292 3 19.
JEFFERIES, R . P. S., 1986. The ilnrestry o j / h ~I.u/ubra/e.r: 376. British M u s r u m (Natural History) and
Cambridge University Press.
JEFFERIES, R. P. S., in press. T h e solute D e r i d r o ~ . w / o i hccotirur from the 1Jppcr Ordovician (if Sccitland and
the shared ancrstry of chordates and echinoderms. Pirlaeon/olo,<y.
JEFFERIES, R . P. S . & LEWIS, D. N . , 1978. 'l'hr English Silurian fossil Placo
ancestry of the vertehratrs. P h l ~ o . ~ n p h i7m1t.~nr/to11.1
~a~
ti/ ihp R y a l ,Socie(v. ( R ) , 282:
JEFFERIES, R . P. S .. LEWIS, M. &. DONOVAN. S.K.. 1987. Protoytiles menezxensi.r a stem-group chordatc
(Cornuta) from the middle Cambrian of Siiuih LValcs. Pa/ueontology, 30: 429484.
JEFFERIES. R. P. S. & P ROKOP, R . J., 1972. A ncw calcichordate from the Ordo\ician of Bohemia and i t s
anatomy, adaptations and relationships. B i o l o , ~ r d.7ournal of the 1,mnean .Soiie!v. 4: 69- I 15.
KOLAT.4, D. R. & JOL L IE , M., 1982. .4nonialocystid mitratrs (Stylophora Echinodrrmata, from the
Champlainian (Middlr Ordovician) Guttcnbcrg Pot-mation of the Upper Lli
Journal nf Paleontolqy, 56: 63 1-653.
KOLATA. D. R., S T R IMPL E , H. L. & LE\'ORSON, C., 1977. Revision of thr Ordov~ciancarpoid family
Iowacystidac. Palaeonlology,20: 529-557.
LOX'TRUP. S., 1977. The Phylogeny of /he Vel-febratn.330 pp. Chirhrster.
LIAI'SUhlO'T'O, H., 1929. Outline of a classification of Echinodermata. Stipnrr Repor/.r o / / h r Tohobu (Impprial)
l.nicersi!v ( 2 , Geology), 13: 27-33.
NELSON, G., 1972. Phylogrnetic relationship n n d clasrilication. .S:vs/mma/ic <oology. P I : 227-231.
NELSON. C;., 1978. Ontogeny, phylogeny, paIc(intolugy and the biogcnctir law. .$vsfcmah <nolo,ip. 27:
324-315.
PARSLEY, R . L., 1988. Feeding and respiratory stratrgirs in Stylophora. I n C. R. C:. Paul 8; A . B. Smith
(Edsj. Erhinoderm PhvIqqenv and Ez,olu/ionary Biolqt.: 347-363, Oxford: Clarcndon Press.
PATTERSON. C.. 1981. Significance of fossils i n determining evolutionary relationships. :intirial Rrri~rc' oJ
Erology and .SyJ/emntic.,, 12: 195-2123,
PA'rI'ERSON, C., 1982. Morphological characters and homology. In K . A. Joysc) &. A . E. Friday (Ed.
Problems nf P/ylogenetic Keconslruclion. Sys/emn/rr\ .4ssoriatton Sperial Folume 21: 2 1-74. London and Nrw Yo
Systematics Association.
PHILIP, G.. 1979. Carpoids echinoderms or chordates? Biological Rez~rew.s.54: 439-47 1.
R E G NAUL T, S. &. CHAUVEL, J., 1987. Dk'ouvcrtc d'un Cchinodermc carpoidc (Stylophot-a Xlitrata 1
dans le Devonien Infirieur du hlaror. G e o b i o ! , 20 ( 5 ) : 669-674.
RIEPPEL, 0 . C., 1988. Fundamvnlals nf Ciimpam/rzv H i d q v . 202pp. Birkhauser.
R O M E R . A . S., 1972. ' r h c vertebrate as a dual iininial sometic and viscrral. Euolulzonnrv H ~ o I N ~6:I . .121 156.
SMI'I'H. A. B.. 1984. Classification of the Echinc~dcrmata.PalaPontologv, 27: 4 3 1 4 5 9 .
~
366
A. P. CRIPPS
SMITH, A. B., 1989. Biomineralisation in echinoderms. In J. G. Carter (Ed.), Skelefal Biomineralisation Patterns,
Processes and Evolutionary Trends. Short Course in Geology, 5(2): 117-147. Washington D.C.: American
Geophysical Union.
SPRINKLE, J., 1983. Patterns and problems in echinoderm evolution. Echinoderm Studies, 1: 1-18.
SZANIAWSKI, H., 1987. Preliminary structural comparisons of protoconodont, paraconodont, and
euconodont elements. In R. J. Aldridge (Ed.), Palaeobiology of Conodonts: 3 5 4 7 . Chichester: Ellis Horwood
Ltd.
THOMSON, K. S., 1987. Spinal discord. (Review of the Ancestry of the Vertebrates.) Nature, 327: 196-197.
UBAGHS, G., 1961. Sur la nature de I’organe appek tige ou pidoncule chez les carpoides Cornuta et Mitrata.
Comptes rendus des Siances de 1’Acadkmie des Sciences, Biol. 253, 2738-2740.
UBAGHS, G., 1969. Les hhinodermes carpoides de l‘Ordouicien Inflrieur de la Montagne Noire. Cahiers de
Paleontologie. 1 12pp. Paris.
UBAGHS, G., 1978. Classification of the echinoderms. T359-T371. In R. C. Moore & C. Teichert (Eds),
Treatise on Invertebrate Paleontology, Part T Echinodermata 2. Vol. 1. 401pp. Boulder and Lawrence.
UBAGHS, G., 1981. Reflexions sur la nature et la fonction de I’appendice articuli: des carpoides Stylophora
(Echinodermata). Annales de Paldontologie (Invertebrates), 67: 33-48.
WILLEY, A,, 1893. Studies on the Protochordata No. 1. O n the origin ofthe branchial stigmata, preoral lobe,
endostyle, atrial cavities etc. In Ciona intestinalis L., with remarks on Clauelina lepadif0rmis. Quarterly Journal of
Microscopical Science ( 2 ) 34: 3 17-360.