BwlagicalJoumal ofthc Linnean .So&& (1997),62: 495-503. With 2 figures
Cladistic information in phylogenetic definitions
and designated phylogenetic contexts for the use
of taxon names
HAROLD N. BRYANT
Provincial Museum of Alberta, 12845-102 Avenue, Edmonton, Alberta T5N OM6, Canada
Received 1 5 November 1996; acceptedfor publication 3 31441997
A phylogenetic definition of a taxon name associates that name with a clade through its
reference to a particular ancestor and all of its descendants. Depending on one’s perspective,
phylogenetic definitions name either clades on the one true, but unknown, phylogeny, or
components on cladograms (clades on hypotheses regarding the true phylogeny). Phylogenetic
definitions do not contain enough information to iden* Components without a reference
cladogram. As a result, (1) if clades are equated with components on cladograms, a
phylogenetic definition may associate a taxon name with different clades on different
cladograms, and (2) the inclusiveness, diagnostic synapomorphies, and distribution in time
and space of the clade with a particular name can differ markedly depending on the
phylogenetic hypothesis one chooses to adopt. This potentially unacceptable lability in the
clade to which a name refers can be avoided by using a taxon name in conjunction with
only phylogenetic hypotheses on which specific taxa are related in a particular fashion. This
de@nated phyfogmtic context can be described in an n-taxon statement that would be appended
to the phylogenetic definition. Use of the taxon name would be considered inappropriate in
conjunction with cladograms on which the relationships contradict those in the n-taxon
statement. Whereas phylogeneticdefinitions stabilize the meaning of taxon names, designated
phylogenetic contexts would stabilize the usage of those names.
0 1997 The Linnean Society of London
ADDITIONAL, KEY WORDS:-clade - component - crown clade - n-taxon statement phylogenetic taxonomy.
CONTENTS
Introduction . . . . . . . . . . . . . .
Perspectives on phylogenetic definitions and clades
Cladistic information in phylogenetic definitions .
Designated phylogenetic context . . . . . .
Acknowledgements . . . . . . . . . . .
References . . . . . . . . . . . . . .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
. . . .
. . . . .
. . . . .
. . . . .
. . . .
. . . .
496
496
497
500
502
502
Correspondence to: Harold N. Bryant, present address: Royal Saskatchewan Museum, 2340 Albert
Street, Regina, Saskatchewan S4P 3V7, Canada.
0024-4066/97/I20495+09 $25.00/0/bj970170
495
Q 1997 The Linnean Society of London
H. N. BRYANT
496
INTRODUCTION
A taxonomy is a scheme of names that can represent either internested classes (a
classification)or the product of a system, such as common descent (Griffiths, 1974;
de Queiroz, 1988). Although the principle of common descent is the central tenet
of modern biology, current biological taxonomy is based on the pre-Darwinian
Linnean hierarchy. De Queiroz & Gauthier (1990, 1992, 1994) have outlined the
basic framework of an alternative, truly phylogenetic taxonomy, with principles and
rules that are formulated based on the principle of common descent. Thus, phylogenetic taxonomy is that part of phylogenetic systematics that represents phylogenetic
relationships through a system of names (de Queiroz & Gauthier, 1992). Given that
taxa are historical entities (species, clades), “taxon names are names of clades” (de
Queiroz & Gauthier, 1992:452) or species. The names of clades are defined through
reference to a particular common ancestor and all of its descendants (Ghiselin,
1984). For example, the name of the clade (A, B) on the left cladogram in Figure
1 could have the node-based definition ‘the most recent common ancestor of A and
B and all of its descendants’. Taxon names can also be defined using stem- or
apomorphy-based definitions (de Queiroz & Gauthier, 1990; see below).
The characteristics (inclusiveness, diagnostic synapomorphies, distribution in time
and space) of the clade named through a phylogenetic definition depend upon the
phylogenetic hypothesis (cladogram) one chooses to adopt as a reference point (de
Queiroz & Gauthier, 1990; Schander & Thollesson, 1995; Bryant, 1996); as a result,
the characteristics of the clade with a particular name can differ considerably on
different cladograms. For example (Fig. l), although the phylogenetic definition
above refers to the clade consisting of only taxa A and B on the left cladogram, on
the right cladogram this definition refers to the clade consisting of all five taxa. This
lability in the inclusiveness, or other characteristics, of clades with particular names
is associated with the limited information regarding phylogenetic relationships in
phylogenetic definitions. This limited cladistic information might be perceived as
allowing unacceptably high instability in the clade with a particular taxon name as
that name is used on cladograms with differing topologies. I propose a mechanism
to deal with this problem whereby taxon names in phylogenetic taxonomy would
be used in conjunction with only particular phylogenetic relationships among specific
taxa.
A
B
C
D
E
B
C
D
A
E
Figure 1. Two hypotheses of relationships among five taxa, illustrating that a change in the phylogenetic
position of a single taxon (A) can result in no equivalent components on the two cladograms despite
the fact that the relationships among the other taxa are the same.
PERSPECTIVES ON PHYLOGENETIC DEFINITIONS AND GLADES
The perceived necessity of restricting the use of taxon names to only certain
phylogenetic hypotheses may be influenced by one’s perspective regarding the clade
DESIGNATED PHYLOGENETIC CONTEXTS FOR TAXON NAMES
497
to which a phylogenetic definition refers. Alternative perspectives are implicit in
differing claims made by de Queiroz & Gauthier (1994) and Bryant (1996). De
Queiroz & Gauthier (1994:30) argued that “under a phylogenetic system of nomenclature, names retain their associations with particular clades or ancestors despite
changes in ideas about relationships”. This statement contrasts with the claim that
the association between taxon names and clades depends not only on the phylogenetic
definition of the name, but also on the particular cladogram one uses as a reference
(Bryant, 1996). Using two contrasting phylogenetic taxonomies of the Carnivora
that were based on different phylogenetic hypotheses (Wolsan, 1993; Wyss & Flynn,
1993),Bryant (1996)argued that some phylogenetic definitions referred taxon names
to different clades on the two reference cladograms.
The view that a phylogenetic definition associates a name with the same clade
regardless of the phylogenetic hypothesis one uses as a reference (e.g. de Queiroz
& Gauthier, 1994) appears to be based on the fact that, given the assumption that
one true phylogeny exists, a phylogenetic definition will associate a taxon name with
only one particular clade on that phylogeny. From this perspective, which focuses
on the true phylogeny and sees that phylogeny as providing the stable reference
point for the identification of clades, our phylogenetic hypotheses do not i d e n e
clades but instead make claims as to the content and other characteristics of those
clades. Because the phylogenetic definition is considered as the mechanism for
permanently linking a taxon name to one clade on the true phylogeny, limiting the
usage of names to only particular phylogenetic contexts might seem to be unnecessary
(but see below).
The perspective implicit to Bryant (1996) focuses, not on the true phylogeny, but
instead on our hypotheses regarding that phylogeny. From this perspective clades
are identified through phylogenetic analyses and are equated with components on
cladograms. Given that there may be several hypotheses regarding the phylogeny
of a particular group of taxa, identification of the same individual clade on two or
more cladograms becomes an issue, as does the question of whether a phylogenetic
definition refers a taxon name to the same clade on different cladograms. Recognition
of this perspective is important to understanding the arguments in Bryant (1996),
especially the claim that the identity of the individual clade referred to by a
phylogenetic definition of a taxon name depends on which cladogram one chooses
as the reference point. Because, from this perspective, the association between taxon
names and clades is not fixed by phylogenetic definitions, the need for limiting the
use of names to only certain phylogenetic hypotheses (cladograms) may be more
apparent.
CLADISTIC INFORMATION IN PHYLOGENETIC DEFINITIONS
Phylogenetic definitions of taxon names lack sufficient information to identlfir a
particular component in the absence of a reference cladogram. Wilkinson (1994:
344) defined components as “statements of relationships that apply, through inclusion
or exclusion, to all taxa under consideration”. A component is a type of cladistically
informative n-taxon statement. An n-taxon statement divides a complete set of taxa
into two subsets; taxa in the inside set are more closely related to each other than
any of these taxa is related to any taxon in the oukide set (Wilkinson, 1994). An ntaxon statement contains cladistic information if “logically possible relationships are
498
H.N. BRYANT
Figure 2. Two hypotheses regarding the relationships among three extant taxa (A, B and E) and two
fossil taxa (C and D; indicated by t),illustrating that phylogenetic definitions can refer a taxon name
to different components on different phylogenies (see text). Both of these cladograms include the
component (A,B,C,D).The component to which the crown clade definition ‘the most recent common
ancestor of A and B and all of its descendants’ refers depends on the relationship among the extant
clades and the two fossil taxa; C and D are excluded from this crown clade on the left cladogram but
are included on the right cladogram. Thus, if clades are components, a crown clade represents a
particular phylogenetic context, rather than an individual clade.
prohibited or conversely when some restricted subset of relationships is asserted”
(Wilkinson, 1994:344). A three-taxon statement (e.g. (A,B)C) is the least inclusive
cladistically informative n-taxon statement (Gafiey, 1979; Nelson & Platnick, 1981;
Wilkinson, 1994).
Components are identified in a phylogenetic analysis through the division of the
terminal taxa under consideration (complete set) between the inside set, those that
are included in the component, and the outside set, those that are excluded from
the component. Thus, in a phylogenetic analysis of taxa A through E (Fig. l), on
the left cladogram A, B and C constitute a component because they form a cluster
to the exclusion of taxa D and E. In other words, components are identified by
determining not only the taxa that are included, but also those that are explicitly
excluded. This component can be represented by the five-taxon statement (A,B,
C)D,E; this n-taxon statement describes a component because n equals five, the
number of taxa included in the phylogenetic analysis (Wilkinson, 1994). The
relationships among the taxa within the component (A, B and C) have no influence
on its individuality or identity; thus, ((B,C)A)is the same component as ((A,C)B)or
((AYBF).
A node-based phylogenetic definition such as ‘the most recent common ancestor
of A and B and all of its descendants’ contains no cladistic information. Two
members (A and B) of the inside set in the equivalent n-taxon statement are identified,
but there is no reference to the outside set. Although node-based definitions refer
to common ancestry, “logically possible relationships” (Wilkinson, 1994:344) are
not prohibited and therefore the definition is compatible with any hypothesis of
relationships. A reference cladogram that includes A and B is required to determine
the node that represents the most recent common ancestor of these two taxa, thus
identiftrlng the component to which the taxon name applies. The association of the
name with a component occurs only within the context of a reference cladogram.
Consider the two cladograms in Figure 2. The phylogenetic definition ‘the most
recent common ancestor of B and D and all of its descendants’ refers to the same
component (A,B,C,D) on both cladograms. In contrast the definition ‘the most
recent common ancestor of A and B and all of its descendants’ refers to a smaller
component (A,B) on the left cladogram but refers to the larger component (A,B,C,
D) on the right cladogram. Given that this definition refers to a smaller component
DESIGNATED PHYLOGENETIC CONTEXTS FOR TAXON NAMES
499
on the left cladogram, even though the larger component is also present, this
definition refers to differentcomponents on the two cladograms. If clades are equated
with components, the clade specified by the definition depends on the particular
cladogram one uses as a reference and phylogenetic definitions can refer names to
different clades on different cladograms (Bryant, 1996).
Stem-based definitions differ from standard node-based definitions in that they
refer to both the inside and outside sets in an n-taxon statement. The stem-based
definition ‘A and all members of X more closely related to A than to D’ explicitly
includes A (inside set) and excludes D (outside set) from the clade being named.
However, these definitions also lack sufficient cladistic information to identrfy a
component in the absence of a reference cladogram. The n-taxon statement may
not be cladistically informative (smu Wilkinson, 1994),and even ifit is, the definition
itself does not indicate whether the n-taxon statement refers to all taxa in a
phylogenetic analysis and therefore identifies an individual component. Because
there may be no ‘members of X more closely related to A than to D’, the definition
above refers explicitly to only two taxa and is therefore equivalent to (A)D, which
is not a cladistically informative n-taxon statement (if the name A has also been
defined phylogenetically, for example as the most recent common ancestor of Y
and Z, one could argue that the above definition is indirectly equivalent to the
cladistically informative n-taxon statement (Y,Z)D). In contrast, the definition ‘A
and B and all members of X more closely related to these taxa than to D’ is directly
equivalent to the n-taxon statement (A,B)D. This definition is incompatible with
cladograms that contradict this n-taxon statement. However, this cladistically informative definition does not identifjr a component because it is uncertain whether
n is equal to all taxa in a phylogenetic analysis. The exclusivity required to identify
an individual component can only be determined through the interpretation of that
definition within the context of a particular cladogram. The cladistic information
in a stem-modified node-based definition (Meng & Wyss, 1994; Wyss & Meng,
1996) such as ‘the clade stemming from the most recent common ancestor of A and
all Recent members of X more closely related to A than to D’ is similar to that of
a standard stem-based definition.
Apomorphy-based definitions make direct reference to no members of either the
inside or outside set in an n-taxon statement. The definition ‘the first species to
possess structure X and all of its descendants’ identifies an ancestor based on the
origin of structure X, but the component to which it refers can only be identified
when the character-state transformations associated with structure X have been
optimized on a reference cladogram.
Given that phylogenetic definitions lack the cladistic information needed to identifjr
particular components in the absence. of a reference cladogram, and if clades
are equated with components (perspective of Wilkinson, 1994; Bryant, 1996), a
phylogenetic definition may associate a name with different clades on different
cladograms. From this perspective, if the maintenance of the association between
taxon names and particular clades is a goal of phylogenetic taxonomy, phylogenetic
definitions may have to be emended when phylogenetic relationships are revised
(Bryant, 1996).
Repeated emending of phylogenetic definitions with on going revisions to phylogenetic hypotheses to preserve the association between taxon names and individual
components would unduly undermine the stability of the nomenclatural system.
Small differences in the position or number of taxa on cladograms can change the
500
H. N. BRYANT
association between taxon names and components. The number of equivalent
components can be reduced, often markedly, by differences in the phylogenetic
position of even a single taxon (Fig. l), and differences in the terminal taxa on
cladograms. In the interests of nomenclatural stability the meaning (wording) of
definitions should be unaffected by differences among phylogenetic hypotheses.
Emending definitions to preserve the association between names and individual
components on cladograms is neither appropriate nor practical. Bryant (1996)
concluded differently that phylogenetic definitions would need to be emended with
revisions to cladograms because he inadvertently attempted to apply a goal consistent
with the perspective of de Queiroz & Gauthier (taxon names should remain associated
with the same clade) to an alternative perspective that views clades as components,
to which this goal is not appropriate.
DESIGNATED PHYLOGENETIC CONTEXT
Because phylogenetic definitions have limited cladistic information, the clade
denoted by a particular name can differ markedly on different cladograms (see
examples in Schander & Thollesson, 1995; Bryant, 1996). This difference may be
viewed in terms of the content of clades (de Queiroz & Gauthier’s perspective) or
the identity of clades (if clades are equated with components). In both instances, the
diagnostic synapomorphies, inclusiveness, and distribution in time and space of the
clade with a particular name can differ depending on the phylogenetic hypothesis
one chooses to adopt. Changes to clades with particular taxon names due to revisions
to phylogenetic hypotheses can potentially undermine the stability in the usage of
those names.
Marked lability in the characteristics of the clade to which a name refers is usually
caused by incorporating names that refer to taxa of uncertain phylogenetic position
in the phylogenetic definitions of taxon names (Schander & Thollesson, 1995; taxon
A in Fig. 1). Many of the phylogeny-dependent differences in the clades to which
the phylogenetic definitions of Wyss & Flynn (1993) and Wolsan (1993)refer (Bryant,
1996: fig. 1) reflect the difference in the position of Amphicyonidae on their
phylogenetic hypotheses. Schander & Thollesson (1995) concluded that this problem
could be avoided by using only names of clades whose relationships are highly
corroborated, and therefore unlikely to change with revisions to phylogenies, in
phylogenetic definitions. However, the likelihood of changes in the phylogenetic
position of taxa cannot always be predicted in advance, and relationships associated
with clades that we wish to name will not always be stable. Some other more broadly
applicable mechanism is needed to deal with differences to the clade to which
a particular name refers that are associated with differences among reference
cladograms.
The source of the stability afforded to the usage of many taxon names defined
using the crown clade convention suggests a solution to this problem. In the crown
clade convention ‘widely known taxon names’ are defined by reference to the most
recent common ancestry of clades with extant members (Gauthier et al., 1989;
Gauthier, Estes & de Queiroz, 1988; Rowe, 1988; de Queiroz & Gauthier, 1992).
For example, Rowe (1987:209) defined Mammalia as “the most recent common
ancestor of its two principal divisions, Monotremata and Theria, and all of its
DESIGNATED PHYLOGENETIC CONTEXTS FOR TAXON NAMES
50 1
descendants.” Although this definition refers explicitly to only Monotremata and
Theria, there is an implicit phylogenetic context associated with the definition in
that the ancestry of these two extant clades is presumed to exclude other extant clades
(e.g.Aves, Crocodylia and Lepidosauria).The common ancestry of Monotremata and
Theria to the exclusion of these other vertebrate clades is highly corroborated and
therefore Rowe’s definition consistently associates the name Mammalia with a clade
that is congruent with this implicit phylogenetic context. Thus, the stability in the
clade named Mammalia by this definition is due in part to stability in the phylogenetic
relationships among particular extant clades. If our hypotheses regarding the
phylogeny of vertebrates changed so that other extant clades were considered more
closely related to Theria than Monotremata is, the name Mammalia would become
associated with a clade with very Werent diagnostic synapomorphies, inclusiveness,
and distribution in time and space, for which the name Mammalia might be deemed
inappropriate. Thus, the phylogenetic relationships for which the use of Mammalia
is appropriate are equivalent to the n-taxon statement ((Monotremata, Theria)
other clades of vertebrates with extant members). This n-taxon statement contains
phylogenetic information that is absent from Rowe’s definition of Mammalia and
denotes the appropriate phylogenetic context for the use of that name. Formal
recognition of the appropriate phylogenetic context for the use of taxon names
would stabilize phylogenetic taxonomy. I define the desz&atedphylogenetic context (similar
in concept to ‘recommended usage’ of Bryant, 1996) for a taxon name as the ntaxon statement that describes the phylogenetic relationships that are considered
appropriate for the use of that name.
Because a standard node-based phylogenetic definition lacks cladistic information,
the appendance to this type of definition of an n-taxon statement that denotes the
designated phylogenetic context for the name would stabilize the usage of that
name. An explicit designated phylogenetic context for Mammalia seems unnecessary
only because views regarding the relationships among the extant clades relevant to
the usage of the name are extremely stable. As a result, use of Mammalia is
appropriate on essentially all cladograms that include monotremes and therians.
Phylogenetic hypotheses relevant to the usage of most taxon names are not as highly
corroborated or stable. Stem-based and stem-modified nodebased definitions with
sufficient and appropriate inherent cladistic information would not require an
appended designated phylogenetic context.
Formal recognition of designated phylogenetic contexts is consistent with the fact
that names of supraspecific taxa are usually associated with specific explicit or
implicit phylogenetic relationships. As a result, it seems appropriate to limit the use
of those names to only trees that have those specific relationships. Gardiner (1982)
proposed that Aves and Mammalia are extant sister taxa and named the crown
clade consisting of these two taxa ‘Haemothermia (emended to Haematothermia
without explanation in Gardiner, 1993). Gardiner’s conceptualization of Haemothermia is based on these specific phylogenetic relationships, which provide the
phylogenetic context for the use of the name. Haemothermia might be defined as
‘the most recent common ancestor of Aves and Mammalia and all of its descendants’,
and its designated phylogenetic context would be the n-taxon statement ((Aves,
Mammalia) other clades of vertebrates with extant members). Because this n-taxon
statement is not congruent with the orthodox view regarding the phylogenetic
relationships among vertebrates, use of Haemothermia is not appropriate within the
502
H.N. BRYANT
context of those cladograms. Nonetheless, use of Haemothermia remains appropriate
within the context of Gardiner’s (1982, 1993) cladograms.
The use of designated phylogenetic contexts will facilitate nomenclatural stability.
Phylogenetic definitions, together with appropriate rules of priority, can establish
and stabilize the meaning of taxon’names, but do not pertain directly to the usage
of those names. Limiting the usage of taxon names to designated phylogenetic
contexts will largely eliminate the need to emend phylogenetic definitions. Instances
may still occur in which the definitions of well known names will need to be emended
to preserve their historical usage (see Carnivora example in Bryant, 1996). Many
of these instances will involve the lack of care in the initial wording of the definition
to allow for possible changes to the clade with revisions to phylogenetic relationships.
Regardless of one’s perspective regarding the clade named by a phylogenetic
definition, stability in the use of taxon names would be facilitated by the recognition
of the appropriate phylogenetic contexts for those names. Because phylogenetic
definitions have limited cladistic information, the phylogenetic context of taxon
names can differ considerably on different cladograms. Phylogenetic definitions of
taxon names without sufficient cladistic information should be accompanied by an
n-taxon statement that denotes the designated phylogenetic context for the use of
the name. This mechanism should discourage the use of the name in conjunction
with cladograms on which the phylogenetic context of the name is not appropriate.
Whereas phylogenetic definitions stabilize the meaning of taxon names, designated
phylogenetic contexts would determine the cladograms with which the name should
be used. As consensus is reached regarding phylogenetic relationships, consensus
will follow regarding the usage of taxon names.
ACKNOWLEDGEMENTS
I thank K. de Queiroz for ongoing discussions of phylogenetic taxonomy. David
Cannatella, Kevin de Queiroz, Mark Wilkinson and two anonymous referees
commented on earlier versions of this paper.
REFERENCES
Bryant HN. 1996. Explicitness, stability, and universality in the phylogenetic delinition and usage of
taxon names: A case study of the phylogenetic taxonomy of the Carnivora (Mammalia). Systematic
Bwbgy 45: 174-189.
de Queiroz K. 1988. Systematics and the Darwinian revolution. Philosophr OfScimce 55: 238-259.
de Queiroz K, Gauthier J. 1990. Phylogeny as a central principle in taxonomy: Phylogenetic
definitions of taxon names. Syskmatic <oologv 39: 307-322.
de Queiroz K, Gauthier J. 1992. Phylogenetic taxonomy. Annual Rariew OfEcohgy and Systematics 23:
449-480.
de Queiroz K, Gauthier J. 1994. Toward a phylogenetic system of biological nomenclature. Tmds
in Ecology and Evolution 9 27-3 1.
Gafhey ES. 1979. An introduction to the logic of phylogeny reconstruction. In: Cracraft J, Eldredge
N, eds. Phylogenetic anabsis andfiabontolo~.New York: Columbia University Press, 79-1 1 1.
Gardiner BG. 1982. Tetrapod classification. <oolOgicalJouml ofthe Linnean Sock9 74: 207-232.
Gardiner BG. 1993. Haematothermia: warm-blooded amniotes. Cladistics 9 369-395.
Gauthier J, Cannatella D, de Queiroz K, Kluge AG, Rowe T. 1989. Tetrapod phylogeny. In:
Fernholm B, Bremer K, Jornvall H, eds. Z?e hierarchy of&. Amsterdam: Elsevier, 337-353.
DESIGNATED PHYLOGENETIC CONTEXTS FOR TAXON NAMES
503
Gauthier J, Estes R, de Queiroz K. 1988. A phylogenetic analysis of Lepidosauromorpha. In:
Estes R, Pregill GK, eds. Phylogenetic rehtionsh$s ofthe l k a d familie.. Essys commemorating Charles L.
Camp. Stanford: Stanford University Press, 15-98.
Ghiselin MT. 1984. ‘Definition,’ ‘character,’and other equivocal terms. Systematic <oology 33: 104-1 10.
Griffiths GCD. 1974. On the foundations of biological systematics. Actu Biotheoretica 23: 85-131.
Meng J, Wyss AR. 1994. Enamel microstructure of Tnbosphmomys (Mammalia, Glires): Character
analysis and systematic implications.Journal ofMamrnalian Evolution 2: 185-203.
Nelson G, Platnick N. 1981. Systematics and biogeography: Ckzdktics and vicariunce. New York Columbia
University Press.
Rowe T. 1987. Definition and diagnosis in the phylogenetic system. Systematic <oology 36: 208-21 1.
Rowe T. 1988. Definition, diagnosis, and origin of Mammalia. Journal of Vkkbrate Paleontology 8:
241-264.
Schander C, Thollesson M. 1995. Phylogenetic taxonomy - some comments. <oologica Smptu 24:
263-268.
Wilkinson M. 1994. Common cladistic information and its consensus representation; reduced Adams
and reduced cladistic consensus trees and profiles. Systm2atiC Biology 4 3 343-368.
Wolsan M. 1993. Phylogeny and classification of early European Mustelida (Mammalia: Carnivora).
Acta 7hniologica 38: 345-384.
Wyss AR, Flynna. 1993. A phylogenetic analysis and definition of the Carnivora. In: Szalay FS,
Novacek MJ, McKenna MC, eds. Mamrnalphylogeny. Phentuls. New York Springer-Verlag, 32-52.
Wyss AR, Meng J. 1996. Application of phylogenetic taxonomy to poorly resolved crown clades: a
stem-modified node-based definition of Rodentia. Systematic Biology 45: 55S568.