Re-assessment of varanid evolution based on new data from Saniwa ensidens Leidy, 1870 (Squamata, Reptilia)

2008·0.82 MB·English

by  Conrad, Jack L

A tamerican museum
Novitates
PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY
CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024
Number 3630, 15 pp., 5 figures December 31, 2008
Re-assessment of varanid evolution based on new
data from Saniwa ensidens Leidy, 1870
(Squamata, Reptilia)
JACK L. CONRAD,1 OLIVIER RIEPPEL,2 AND LANCE GRANDE2
ABSTRACT
Saniwa ensidens is a pivotal taxon for understanding varanid evolution. A complete specimen of
Saniwa ensidens was recently described, offering important new insights into the morphology of
this taxon. We apply these new data to a broader-scale study of squamate relationships in order to
understand the phylogenetic position of Saniwa ensidens and of varanids more generally. Among
the other fossils included in our analysis were the Eocene taxon “Saniwa” feisti, the Miocene
Varanus rusingensis, and the giant Pleistocene varanid Megalania prisca. We compare the
phylogenetic hypothesis from our analysis of morphology with a recent molecular-based
hypothesis and find numerous differences in the phylogenetic relationships within Varanus. We
constrained our morphological data set to the phylogenetic pattern presented by the molecular
data to further analyze the possible phylogenetic relationships of the fossil taxa. Our analyses show
that Saniwa ensidens is the sister taxon to crown-group Varanus and that “ Saniwa” feisti is a basal
member of the varanid lineage, not closely related to Saniwa ensidens. Both Varanus rusingensis
and Megalania prisca are members of the crown radiations of Varanus.
INTRODUCTION lizards (Varanidae) (fig. 1). Rieppel and
Grande (2007) recently described an excep¬
Monitor lizards and their fossil relatives tionally well-preserved specimen of Saniwa
compose a speciose squamate clade with a ensidens from “Locality H” within the Eocene
deep fossil record. Saniwa ensidens is an deposits of Fossil Lake, Wyoming (see Grande
Eocene squamate universally regarded as and Buchheim, 1994). This new specimen
having some affinity with modern monitor offers insights that improve the understanding
1 Department of Vertebrate Paleontology, American Museum of Natural History ([email protected]).
2 Department of Geology, the Field Museum, 1400 S Lake Shore Drive, Chicago, Illinois 60605-2496 (orieppel@
fieldmuseum.org; [email protected]).
Copyright © American Museum of Natural History 2008 ISSN 0003-0082
2 AMERICAN MUSEUM NOVITATES NO. 3630
Fig. 1. Skulls of three varanines in dorsal view: (A) Saniwa ensidens (reconstructed based on FMNH PR
2378), (B) Varanus albigularis (AMNH R 47726), and (C) Varanus gouldii (drawn after Maisano, 2001b).
Note the general conservation of features between the three taxa. Saniwa ensidens possesses a greater
contribution of the prefrontal to the dorsal skull roof and that the maxillae extend further dorsomedially
(Rieppel and Grande, 2007). Reconstructed portions Saniwa ensidens are shown as semi-opaque shadows to
minimize the morphology they hide. Note that the right palpebral has been removed from Varanus
albigularis and that this taxon has a large and elaborate septomaxilla. Abbreviations: e, epipterygoid; n,
nasal; pap, palpebral; sm, septomaxilla.
of the placement of Saniwa ensidens among of Varanus have been based on molecular data
varanoids. Additionally, incorporation of new (Fuller et al., 1998; Ast, 2001, 2002b; Pepin,
morphological data may help to resolve the 2001), which cannot address the position of
interrelationships of other fossil varanoids and fossil taxa. The fossil taxa Megalania prisca
within the genus Varanus through a better and Varanus rusingensis have never been
understanding of character polarities and included in a cladistic analysis focusing on
character evolution. relationships and interrelationships of
Many fossil squamates have been suggested Varanus. Additionally, various fossils too
as being close relatives of modern varanids incomplete to be included here have been
(e.g., Megalania prisca, Saniwides mongolien- referred to the Varanidae. Noteworthy is the
sis, Telmasaurus grangeri), but with only Middle Miocene Iberovaranus (Hoffstetter,
limited cladistic analysis of these relationships. 1969; Estes, 1983), which could be an early
Conrad (2008) recently provided an extensive occurrence of Varanus or proximal outgroup,
morphological data matrix addressing global but whose position cannot be analyzed with¬
squamate relationships. Norell et al. (2008) out the discovery of more complete remains.
further expanded on this analysis, adding Varanus contains 68 extant species accord¬
several additional varanid species and mor¬ ing to Uetz (2008) with a size range rivaling
phological characters. that between rats and elephants (Pianka,
Importantly, the interrelationships within 1995). Although many aspects of the osteolo¬
Varanus have not been directly addressed in gy of Varanus are conservative, some details
an analysis also analyzing the phylogenetic are variable between species (see Mertens,
placement of Saniwa ensidens. Recent analyses 1942c) (fig. IB, C). Given such diversity, it is
2008 CONRAD ET AL.: VARANID EVOLUTION 3
problematic that most morphology-based Saniwa ensidens based on the complete skeleton
analyses code Varanus as a single terminal (FMNH PR 2378) and a cast of a partial skull
taxon without reference to a particular species (FMNH PR 2380) recently described by
or phylogenetic hypothesis of Varanus inter¬ Rieppel and Grande (2007).
relationships. Lanthanotus borneensis, the ex¬ Analysis 1: We analyzed these data using
tant sister group to Varanus (Pregill et al., the computer program T.N.T. (Goloboff et
1986; Estes et al., 1988; Wu et al., 1996; Evans al., 2003) using the New Technology Search
and Barbadillo, 1998, 1999; Gao and Norell, (1000 replicates) and three subsequent ratchet
1998; Lee, 1998; Evans et al., 2005; Conrad, runs (each of 1000 replicates). Our analysis
2008; but see Northcutt, 1978 and Caldwell, recovered 2373 equally short trees, each with a
1999), does not help much in reconstructing length of 3846 steps and a retention index of
the basal Varanus morphology because it is 0.7138.
very derived when compared with primitive We report both the strict and Adams
varanoids, monstersaurs, and fossils previous¬ consensus trees for taxa of interest (fig. 2),
ly allied with varanids. A better understanding the latter as reconstructed by the computer
of the interrelationships of Varanus species program PAUP* (Swofford, 2001). Adams
and Lanthanotus in the context of their fossil consensus trees are reported rather than
relatives could offer new insights into charac¬ majority-rule trees. Adams consensus collap¬
ter polarities within Varanidae and its stem ses problematic/volatile taxa to their most
lineage, and help in accurately identifying the basal supported position and retains branches
basal character states among the species of that are supported in all of the principle trees,
Varanus. regardless of the position of volatile taxa.
Here, we will add to recent analyses in order Analysis 2: To further test the position of
to further elucidate the phylogenetic place¬ Saniwa ensidens and other fossil varanids, such
ment of Saniwa ensidens, the phylogenetic as Megalania prisca and Varanus rusingensis,
interrelationships of other proximal varanid we created a subset of the data containing
outgroups, and the interrelationships of only “Saniwa'’'’ feisti, Necrosaurus cayluxi,
Varanus species. Saniwides mongoliensis, Telmasaurus grangeri,
Aiolosaurus oriens, Lanthanotus borneensis,
MATERIALS AND METHODS Cherminotus longifrons, Ovoo gurvel, Saniwa
ensidens, Megalania prisca, and all of the
Data Matrix: A number of studies have Varanus species present in the global analysis
investigated the relationships of varanids and described above (reduced matrix A). These
the interrelationships of Varanoidea over the data were then analyzed in the same manner
last five decades (McDowell and Bogert, 1954; as the global data (see above). Because the
Rieppel, 1980a; Branch, 1982; Borsuk- results of this analysis were very similar to
Bialynicka, 1983, 1984; Pregill et al., 1986; those of the global analysis (see below), the
Estes et al., 1988; Norell et al., 1992; Pianka, RMA was used for further tests that would
1995; Caldwell, 1996; Dal Sasso and Pinna, have been prohibitively time-consuming or
1997; Lee, 1997; Caldwell, 2000; Lee and impossible given the global data matrix.
Caldwell, 2000; Nydam, 2000; Rieppel and Analysis 3: We ran a third analysis in
Zaher, 2000a; Pepin, 2001; Rieppel et al., 2006; which only extant taxa were included for
Conrad, 2008; Norell et al., 2008). Most comparison with a recent molecular phyloge-
recently, Conrad (2008) presented an extensive ny of varanids (Ast, 2001, 2002a). Ast’s (2001)
morphological analysis of squamate relation¬ study was chosen for comparison because it is
ships. Norell et al. (2008) augmented this one of the most taxonomically inclusive and
analysis by adding 29 taxa (including the basal one of the most recent molecular-based studies
varanine Ovoo gurvel) and nine new characters. of extant varanoid interrelationships. Fuller et
To this matrix of 251 taxa and 373 characters al. (1998) and King et al. (1999) have also
we have now added four more Varanus species recently analyzed varanid interrelationships
{Varanus albogularis, Varanus gilleni, Varanus using molecular data and produced a phylo¬
rudicollis, and Varanus salvator) and coded genetic hypothesis that is generally similar to
4 AMERICAN MUSEUM NOVITATES NO. 3630
mosasaur lineage f
Saniwa" fmsti t Adams
Necrosaurus cayiuxi t
Saniwides mongoiiensis t
Teimasaurus granger! |
Aiolosaurus oriens t
Lanthanotus bomeensis
Cherminotus longifrons t
Ovoo gurvel t
Saniwa ensidens t
acanthurus
semiremex
gilleni
eremius
tristis
prasinus
kordensis
rudicollis
olivaceus
dumerilii
indicus
flavescens
rusingensis t
Varanus Varanus
griseus
exanthematicus
niioticus
albigularis
gouldii
bengalensis
saivator
varius
komodoensis
salvadorii
priscus f
Fig. 2. Strict (left) and Adams rule (right) consensus cladograms representing areas of interest from the
global analysis of squamate relationships described in the text (note, non-varaniform taxa omitted). Extinct taxa
are denoted by daggers (t). Groups A and B (from the text) are identified here and referred to again in figure 4.
that of Ast (2001), but the latter was slightly and the analysis of Ast (2001) were forced into
more taxonomically inclusive. Pianka (1995) the topology of the latter study. This con¬
recovered a slightly different result, using straint tree was treated as a “backbone”
different techniques. Fitch et al. (2006) ana¬ constraint in PAUP* so that nonoverlapping
lyzed relationships among a subset of Varanus, taxa were could be placed within the con¬
and their results generally agree with those of straint tree.
Ast (2001). Data Acquisition: Morphological data
Analysis 4: Finally, we constructed a were acquired through direct observations of
constraint tree for reduced matrix A (RMA) specimens (appendix 1) and published data.
in which the extant taxa common both to it Published data were used to supplement the
2008 CONRAD ET AL.: VARANID EVOLUTION 5
codings for some extant Varanus (Mertens, recovering the mosasauroid clade as interme¬
1942a, c, b; Bellairs, 1949; McDowell and diate between “gobidermatids” and crown-
Bogert, 1954; Rieppel, 1980a; Jenkins and group Varanoidea. Norell and Gao (1997)
Goslow, 1983; Landsmeer, 1983; Rieppel, point out that one of the weaknesses of Lee’s
1993; Pianka, 1995; Zaher and Rieppel, (1997) (and, by extension, Pepin’s 1999)
1999a; Rieppel and Zaher, 2000b; Maisano, study is that it assumes the monophyly of a
2001b; Pepin, 2001; Rieppel and Grande, clade containing Gobiderma pulchrum and
2007; Uetz, 2007), Lanthanotus (McDowell Parviderma inexacta, even though there is no
and Bogert, 1954; Rieppel, 1980a, b, 1983; evidence to suggest such a relationship.
Zaher and Rieppel, 1999b, a; Maisano, 2001a; Indeed, Gao and Norell (1998) offer evidence
Rieppel and Zaher, 2000b; Maisano et al., suggesting that Gobiderma pulchrum is a
2002), the included Gobi taxa (Gilmore, 1943; monstersaur (closer to Heloderma than to
Borsuk-Bialynicka, 1983; Estes, 1983; Borsuk- Varanus) and Parviderma inexacta may be
Bialynicka, 1984; Gao and Hou, 1996; Gao more closely related to varanids. Other weak¬
and Norell, 1998, 2000), Saniwa ensidens nesses of the Lee (1997) study are its
(Gilmore, 1928; Estes, 1983; Caldwell, 2003; constraint of snakes as platynotans and the
Rieppel and Grande, 2007), Megalania prisca selection/construction of some of the morpho¬
(Hecht, 1975; Molnar, 1990, 2004; Lee, 1995; logical characters (see Zaher and Rieppel,
Erickson et al., 2003), and Varanus rusingensis 1999b, a). Gao and Norell (1998) offer a
(Clos, 1995). different hypothesis of relationships, based on
a broader sampling of fossil and extant taxa,
Monospecific Taxa: Note that Aiolosaurus
but including neither snakes nor mosasaur¬
oriens, Cherminotus longifrons, Lanthanotus bor-
oids. Conrad (2008) suggests that snakes are
neensis, Saniwides mongoliensis, Telmasaurus
not closely related to anguimorphs, but that
grangeri are each monospecific and may, hereaf¬
they are scincoids.
ter, be referred to by their generic names only.
PREVIOUS ANALYSES
RESULTS
Saniwa ensidens has a long history of
Search Results
systematic association with varanids (see, for
example, Camp, 1923, Gilmore, 1928, and Analysis 1: Our global analysis recovered
McDowell and Bogert, 1954) and resembles 2373 equally short trees, each with a length of
extant varanids in cranial morphology. Other 3846 steps and a retention index of 0.7138.
fossil taxa such as Aiolosaurus oriens, Both strict and Abrams consensuses are
Cherminotus longifrons, Proplatynotia longir- illustrated (fig. 2).
ostrata, Saniwides mongoliensis, and Telma¬ Analysis 2: Our analysis of reduced ma¬
saurus grangeri are also similar to Varanidae trix A (RMA) recovered 144 equally short
(Gilmore, 1943; Borsuk-Bialynicka, 1984; Lee, trees, each with a length of 288 steps and a
1997; Gao and Norell, 2000), and many of retention index of 0.5621. Only the Adams
these taxa have been referred to Varanidae in consensus of this search is illustrated (fig. 3).
the past. Analysis 3: The analysis limited to extant
Four recent studies have addressed many of taxa recovered three equally short trees, each
these taxa. Lee (1997) presents a phylogenetic with a length of 204 steps and a retention
hypothesis in which Proplatynotia longirostra- index of 0.4729. The strict and Adams
ta and Paravaranus angustifrons are the sister consensuses for this analysis are identical
taxa to the extant varanoids, Telmasaurus is (see fig. 4).
the sister taxon to a clade containing varanids, Analysis 4: The analysis run with a
mosasauroids, and snakes, and Saniwa ensi¬ backbone constraint for extant varanids re¬
dens and Saniwides are successively closer covered 70 equally short trees, each with a
sister taxa to the extant Varanus. Pepin length of 308 steps and a retention index of
(1999) presents a very similar analysis, but 0.5056. The results of this analysis are
resolves the interrelationships more fully, described more fully below.
6 AMERICAN MUSEUM NOVITATES NO. 3630
"Saniwa• feisti ■[ Lanthanotus borneensis
Necrosaurus cayluxi t flavescens
Saniwides mongoliensis t indicus
Teimasaurus grangeri f rudicollis
Aiolosaurus oriens f griseus
Lanthanotus borneensis exanthematicus
Cherminotus longifrons f niioticus
Ovoo gurvel f
albigularis
Saniwa ensidens t oiivaceus
semiremex
dumeriUi
gitleni
bengaiensis
eremius
salvator
tristis
gitleni
prasinus
eremius
kordensis
semiremex
acanthurus
tristis
rudicoltis
prasinus
oiivaceus
kordensis
dumeritii
acanthurus
indicus
flavescens goutdii
varius
A
komodoensis
B
saivadorii
Fig. 3. Analysis from reduced matrix A (RMA)
Fig. 4. Phylogenetic hypothesis generated by
analysis. See the text for details. Groups A and B
analysis of the RMA when all fossil taxa are
are identical in their topology to those denoted in
deleted. Note that this topology shows similarities
figure 2.
with the morphological analyses in figures 2 and 3,
and also with that of the molecular analysis of Ast
Systematic Results (2001) (fig. 5).
Character list: The complete list of
characters and character states are found in 233(1) presence of at least weak precondylar
Conrad (2008) and Norell et al. (2008). Both vertebral constriction. “Saniwa” feisti and
of these papers are available for free in pdf Necrosaurus cayluxi form a polytomy at the
format from http://digitallibrary.amnh.org/ base of this clade. This and other polytomies
dspace. The data are presented in a format within the results of this analysis may be
that allows them to be copied and pasted to a present, in part, because of the inclusion of
new document in nexus format, T.N.T. incomplete specimens. Saniwides, Teimasaurus,
(Goloboff et al., 2003) format, etc. and crown-group varanids form a clade based
Clade Diagnoses: According to the cur¬ on 55(0) presence of separate (unfused) frontals
rent study, “Saniwa” feisti, Necrosaurus cay¬ in adults, 70(0) presence of a U-shaped
luxi, Saniwides, Teimasaurus, and crown- frontoparietal suture, 124(1) presence of an
group Varanidae form a clade based on five ectopterygoid-palatine contact anterior to the
unambiguous synapomorphies. These are suborbital fenestra, and 183(1) dorsal dentary
58(0) straight (linear) interorbital frontal contribution to the anterior inferior alveolar
margins, 61(1) subolfactory processes of the foramen. Within this clade, Teimasaurus and
frontals partly surrounding the olfactory Saniwides form an exclusive clade diagnosed by
tracts of the brain, 65(1) presence of an 115(0) presence of palatine tooth patches, and
external maxillofrontal contact, 115(2) pres¬ 118(0) pterygoid teeth arranged in multiple
ence of a single line of palatine teeth, and rows/patches.
2008 CONRAD ET AL.: VARANID EVOLUTION 7
Varanidae is typically considered to include Varanus rusingensis and Megalania prisca
extant Varanus, Lanthanotus, and all descen¬ (hereafter Varanus prised) are both nested
dants of their last common ancestor (Pregill et within the extant Varanus radiation according
al., 1986; Estes et al., 1988; Pianka, 1995; Lee, to this analysis. Varanus prisca is the sister
1998; Bernstein, 1999; Conrad, 2004, 2008). taxon to Varanus salvadorii, sharing with it
The current analysis recovers five unambigu¬ 69(0) absence of parietal tabs on the frontal.
ous synapomorphies for Varanidae including Varanus komodoensis forms a clade with
Aiolosaurus. Aiolosaurus forms a polytomy Varanus prisca and Varanus salvadorii based
with lanthanotines and varanines in this on 32(1) presence of a medial palatine flange
analysis (for a review on the phylogenetic on the maxilla and 111(0) palatine longer than
placement of Aiolosaurus, see Norell et al., wide. Varanus varius is the next most proximal
2008). The five character states supporting sister taxon and shares with the other species
Varanidae are 3(1) presence of a blunt and listed 3(1) a blunt, rounded snout and 372(0)
rounded snout, 65(0) absence of an external distal placement of the fleshy external nares.
maxillo-frontal contact, 149(1) presence of a Varanus salvator shares with these other taxa
broad crista tuberalis that incorporates the three unambiguous synapomorphies, includ¬
paroccipital processes, 151(1) an anteriorly ing 72(1) broad and squared lateral flange of
placed spheno-occipital tubercle, and 178(0) a the parietal at the frontoparietal suture, 138(1)
ventrally arched dentary. The Cherminotus- reduced crista prootica without a distinct
Lanthanotus clade is supported by 32(1) ventral extension, and 189(1) splenial extend¬
presence of a medial palatine flange on the ing for less than one-half the dentary length.
maxilla, 83(1) presence of a nuchal fossa at the Varanus gouldii and Varanus bengalensis form
posterior margin of the parietal, and 107(0) a polytomy with the salvator-varius-komodoen-
presence of a rod-shaped vomer. sis-salvadorii-prisca group in a clade hereafter
Varaninae (sensu Pregill et al., 1986 as referred to as “group A”. Group A is
modified by Conrad, 2008; all taxa sharing a diagnosed by 1(3) an extremely elongate
more recent common ancestor with Varanus antorbital snout (constituting more than half
varius than Lanthanotus borneensis) is here the craniobasal length) and 233(2) vertebrae
diagnosed by 27(1) presence of a midline with strong precondylar constriction.
contact of the maxillae posterior to the Group A forms a polytomy with Varanus
premaxillary nasal process, 51(1) absence of flavescens and a clade containing the mostly
a jugal-postorbital contact, and 62(1) midline African taxa Varanus albigularis, Varanus
contact of the subolfactory processes on the exanthematixus, Varanus griseus, Varanus
frontals. Saniwa ensidens is found to be the niloticus, and Varanus rusingensis; hereafter
sister taxon to crown-group Varanus in all the referred to as “group B”. Group B is united by
principle trees in this analysis. The six a single unambiguous synapomorphy, which is
unambiguous synapomorphies uniting this 212(5) presence of globidont posterior teeth.
clade are 3(0) presence of a tapering snout All of group B besides the Miocene Varanus
(fig. 1) (reversed in some Varanus), 10(1) rusingensis form an unresolved clade united by
presence of dermal sculpturing on the frontal 292(0) presence of a separate astragalus and
and parietal, 42(1) presence of a posterolateral calcaneum.
lacrimal flange, 43(1) a double lacrimal Group A, group B, and Varanus flavescens
foramen, 44(1) an enlarged primary lacrimal form a clade with Varanus indicus; united by
foramen, and 111(0) palatine longer than 141(1) presence of a double facial foramen and
wide. The species of Varanus are united to 312(0) absence of keeled scales on the body.
the exclusion of Saniwa ensidens based on the This clade, in turn, forms a polytomy with
following synapomorphies: 52(2) Jugal lying Varanus rudicollis and a clade composed of
mostly posterior to the maxilla, with little or Varanus dumerilii and Varanus olivaceus. This
no overlap, 69(1) presence of parietal tabs on clade is diagnosed by 20(1) fused nasals and
the frontal, 74(1) frontal tabs present on the 111(1) palatine subequal in length and width,
parietal, 115(1) absence of palatine teeth, and and forms a polytomy with other Varanus
118(2) absence of pterygoid teeth. (fig. 2).
AMERICAN MUSEUM NOVITATES NO. 3630
Comparisons with molecular studies: The respect to clades A and B, but resolved the
analysis above differs significantly from the position of Varanus acanthurus as a sister-
phylogenetic hypothesis of the interrelation¬ taxon to Varanus rudicollis. All of the more
ships of Varanus proposed by Ast (2001), basal taxa on the varanid lineage remained in
although there are several points of congru¬ the same position as with the global analysis.
ence (compare figs. 2, 3, and 5). Notably, both The RMA is used in the following analyses.
analyses recover a clade containing the large¬ Analysis 3 (extant-only analysis) (fig.
bodied taxa Varanus komodoensis, Varanus 4): We re-analyzed RMA with all fossil taxa
salvadorii, and Varanus varius and a clade deleted, in part, to test the importance of
containing the African taxa Varanus exanthe- fossils in our analysis and to isolate possible
maticus, Varanus griseus, and Varanus niloti- similarities in the signal between the molecular
cus. In contrast to Ast (2001), we find no data and our morphological data.
support for major Indo-Asian clades. Instead When all fossil taxa are deleted from the
these clades are found to be paraphyletic or RMA, we recover an Indo-Asian monitor
polyphyletic with respect to African and Indo- clade consisting of the taxa Varanus olivaceus,
Australian clades. The Indo-Australian group Varanus bengalensis, and Varanus dumerilii.
(as identified by Ast, 2001) is not monophy- The interrelationships of these three taxa is
letic. Varanus bengalensis and Varanus Salva¬ that revealed by Ast’s (2001) analysis, but with
tor are found to belong to the otherwise several other taxa removed; that is, some of
mostly Indo-Australian clade termed group A the Indo-Asian taxa common to both analyses
above. Ast (2001) found Varanus bengalensis (see the right side of fig. 5) fall outside of the
and Varanus salvator to be nested members of Indo-Asian clade recovered in our extant-only
the Indo-Asian A clade in her study. Most of analysis. Ast (2001) finds Varanus flavescens
the other members of Ast’s (2001) Indo-Asian and a clade composed of Varanus rudicollis
clades included in our global analysis form a and Varanus salvator to be successively more
paraphyletic assemblage representing proxi¬ remote sister taxa to her Varanus bengalensis-
mal sister taxa to the clade including groups A Varanus dumerilii clade. She also finds
and B. Varanus prasinus and Varanus indicus to be
Taxonomic inclusiveness is a key consider¬ nested members of a clade including Varanus
ation when comparing and contrasting these olivaceus (Ast, 2001). In the current analysis of
analyses. Ast’s (2001) analysis is more taxo- extant taxa, Varanus flavescens, Varanus
nomically inclusive amongst extant taxa, and indicus, and Varanus rudicollis are suggested
she included multiple “subspecies” and/or to be basal Varanus species. Varanus salvator
specimens from multiple localities for many is recovered as the sister taxon to a mostly
species. By contrast, our morphological anal¬ Indo-Austalian clade including taxa typically
yses (above and below) benefit from the assigned to the clade Odatria (e.g., Varanus
inclusion of fossil taxa (e.g., Saniwa ensidens) acanthurus) and some large-bodied varanids
that may, in some cases, offer a clearer (e.g., Varanus gouldii and Varanus komodoen¬
understanding of the primitive morphology sis)', Varanus prasinus is nested within our
for some nodes and certainly help to polarize Indo-Australian clade. Our extant-only anal¬
characters throughout the tree. We will further ysis recovered Varanus gouldii as a basal
investigate these considerations below. member of the clade containing Varanus
varius, Varanus komodoensis, and Varanus
salvadorii, whereas Ast (2001) recovered it as
Results of Comparative Analyses
more closely related to the Indo-Asian clades
Analysis 2 (RMA analysis): Analysis of (but see Ast, 2002b).
RMA reveals a very similar Adams consensus Thus, similarities between the extant-only
tree to that of the global analysis (compare analysis performed here and the molecular
figs. 2 and 3). Clades A and B were identical analysis (Ast, 2001) not present in analyses 1
between the two analyses. Adams consensus of or 2 above include the recovery of an Indo-
the RMA analysis was unable to resolve the Asian clade and consolidation of Indo-
relative position of Varanus flavescens with Australian taxa into a single clade (figs. 2, 3,
2008 CONRAD ET AL.: YARANID EVOLUTION 9
griseus
Ast (2001, 2002b) exanthematicus Ast (2001,2002b)
all species included niloticus species overlapping
with current study
ffavescens
dumerilii
bengaiertsis
rudicollis
salvator
olivaceus
prasinus
beccari
kiethhomei
jobiensis
doreanus
yuwoni
melinus
indicus
semiremex
mitchelli
timorensis
scalaris
giauerti
tristis
glebopalma
pilbarensis
eremius
gilleni
kingorum
primordius
atom
acanthurus
baritji
panoptes
gouldii
giganteus
mertensi
spenceh
salvadohi
varius
komodoensis
Fig. 5. Phylogenetic hypothesis for the extant Varanus species as presented by Ast (2001, 2002a). The left
side shows all of the species included in her analysis. The right side is a cladogram of the same topology, but
with only the species included in both Ast (2001, 2002a) and the current morphological analysis.
10 AMERICAN MUSEUM NOVITATES NO. 3630
5). This result raises the possibility that the in possessing a more anteriorly extensive jugal,
absence of historical morphological data a simpler frontoparietal suture, and in the
provided by fossils may be a factor in the plesiomorphic retention of palatal teeth. The
recovery of those clades by molecular analy¬ overall appearance of the skull roof of Saniwa
ses. Inclusion of fossil outgroups to Varanus ensidens is similar to that of extant Varanus,
(e.g., Saniwa ensidens) and fossil Varanus (e.g., especially given the diversity present in the
Varanus rusingensis) apparently repolarize latter (see fig. 1 and Mertens, 1942a, b, c,
character states such that the attraction of 1942c).
some Indo-Asian taxa and the two main Some other taxa sometimes considered close
clades of Indo-Australian taxa is reduced. relatives of Varanus are actually outgroups to
However, the possibility remains that there the crown-group Varanidae. Saniwides mon-
also may be undetected morphological ten¬ goliensis and Telmasaurus grangeri form a
dencies associated with becoming large, lead¬ clade that is one of the proximal outgroups to
ing to convergence between Varanus salvator, Varanidae in our analysis. This conclusion
Varanus gouldii, and the large-bodied Indo- contrasts with those of some earlier studies
Australian taxa within morphological phylo¬ (e.g., Lee, 1997 and Pepin, 1999), which
genetic analyses. Molecular data may be less suggested Saniwides formed a clade with
susceptible to this bias, and the problem of Varanus exclusive of Saniwa ensidens. The
subjectivity present in morphological charac¬ recently described specimens of Saniwa en¬
ter formulation. sidens have clarified similarities between that
Analysis 4 (constrained tree analysis): Our taxon and Varanus.
constrained tree analysis was designed to test Varanus rusingensis is probably the oldest
the placement of fossil taxa given the context known member of the extant Varanus radia¬
of the molecular phylogeny presented for tion. The only doubt about this hypothesis is
Varanus by molecular evidence. raised by a small subset of the trees generated
Saniwa ensidens was found to be the sister from the constrained analysis described above
taxon to Varanus in all of the principle trees (analysis 4). This taxon demonstrates that the
recovered in this analysis. Varanus rusingensis Varanus clades had diversified by and reached
was somewhat variable in its placement. It was Africa no later than the Early Miocene (Clos,
variably recovered as the sister taxon to all of 1995). “Megalania” prisca is confirmed to fall
other Varanus, to Varanus olivaceus, or to within the extant radiation of Varanus.
Varanus flavescens. Varanus prisca was con¬ Inclusion of Incomplete Fossils: As is
sistently recovered in a nested position within often the case, inclusion of fossils in this
the extant Varanus radiation. It was variably analysis also means the inclusion of taxa that
found to be the sister taxon to Varanus cannot be scored for every character state.
salvadorii, the sister taxon to Varanus varius, Indeed, many of the extant taxa were coded
the sister taxon to a clade containing Varanus from incomplete specimens or species for
varius and Varanus komodoensis, or the out¬ which specific knowledge of some character
group to a clade containing Varanus komo¬ systems (e.g., some soft characters) could not
doensis, Varanus salvadorii, and Varanus be scored. Inclusion of these additional data
varius. will benefit future iterations of this analysis
pending fuller description of specific taxa and/
DISCUSSION or discovery of more complete fossils.
Conclusions about Clades of Varanus:
Fossil Varanidae Conclusions: Saniwa The interrelationships of the Varanus clades
ensidens is a pivotal taxon for understanding have been approached both using molecular
the evolution of the varanid lineage because of and morphological data. Ast’s (2001) relative¬
its placement and the completeness of the ly inclusive analysis of extant Varanus pro¬
known remains. Our analyses confirm the duced a result that differs significantly from
placement of Saniwa ensidens as the sister our morphology-based global analysis, which
taxon to Varanus within Varaninae (fig. 2). included numerous nonvaranids, fossil vara-
Saniwa ensidens differs from Varanus mainly nids, and several extant Varanus. Taxon