A new platynotan lizard (Diapsida, Squamata) from the late Cretaceous Gobi Desert (Ömnogöv), Mongolia

2008·1.5 MB·English

by  Norell, Mark

A tamerican museum
Novitates
PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY
CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024
Number 3605, 22 pp., 7 figures April 9, 2007
A New Platynotan Lizard (Diapsida: Squamata) from
the Late Cretaceous Gobi Desert
(Omnogov), Mongolia
MARK A. NORELL,1 KE-QIN GAO,2 AND JACK CONRAD3
ABSTRACT
Here we describe a new diminutive varanoid from the Late Cretaceous Djadoktha Formation of
Omnogov, Mongolia. The new taxon, Ovoo gurval, was found in the Nemegt Basin at the locality
of Little Ukhaa, a locality adjacent to the rich fossil beds of Ukhaa Tolgod. The new varanoid is
similar to Aiolosaurus oriens, another small varanoid from the Ukhaa Tolgod locality and several
diagnostic characters of Ovoo gurval are shared with Aiolosaurus oriens. Ovoo gurval also has a
pair of unusual neomorphic ossifications on the skull roof overlying the frontonasal contact.
Positionally, these are unlike any neomorphic ossifications in other squamates, and certainly can
be distinguished from osteoderms found in some varanoids.
INTRODUCTION Djadoktha specimens represent a remarkable
diversity, and especially with respect to
Localities in Djadoktha and Djadoktha-like varanoid lizards, which are usually only rarely
rocks (see Loope et al., 1998; Dashzeveg et al., encountered in fossil deposits. Well-preserved
2005; Dingus et al., in press) have produced an varanoids are important because not only is
extensive lizard fauna. Notable among these there an impressive living diversity (Pianka,
localities is Ukhaa Tolgod, which has pro¬ 1995; Norell, 2004), but they also may hold
duced several thousand specimens of fossil the clues necessary to pinpoint the origins of
lizards (Dashzeveg et al., 1995). The groups like mosasaurs, aigialosaurs, and
1 Division of Paleontology, American Museum of Natural History ([email protected]).
2 Department of Geology, Peking University, Beijing 100871, People’s Republic of China; Research Associate, Division
of Paleontology, American Museum of Natural History ([email protected]).
3 Division of Paleontology, American Museum of Natural History ([email protected]).
Copyright © American Museum of Natural History 2008 ISSN 0003-0082
2 AMERICAN MUSEUM NOVITATES NO. 3605
snakes. This paper describes a diminutive new
varanoid lizard (IGM 3/767) from a Late
Cretaceous deposit exposed in the Gobi
Desert, Mongolia.
ABBREVIATIONS
Institutional
AMNH-R American Museum of Natural
History, Division of Vertebrate
Zoology, Reptiles
IGM Institute of Geology, Mongolian
Academy of Sciences
FMNH Field Museum of Natural History
IGM Institute of Geology, Mongolian
Academy of Sciences
Anatomical
Fig. 1. Map showing the type locality in rela¬
Uppercase L and R as prefixes signify left tion to other fossil localities in the Gobi Desert.
and right respectively.
eh choana
dplf dorsal posterior lacrimal foramen
ect ectopterygoid
f frontal covered in 1996 (figs. 1, 2); it has produced
iof infraorbital foramen a diverse assemblage of dinosaurs, lizards,
j jugal articulation and mammals and shares faunal similarity
1 lacrimal
with Ukhaa Tolgod, but it may represent
m maxilla
a slightly different age or environment due
mb mystery bone
to the presence of Bagaceratops (a
n nasal
na naris Barungoyotian protoceratopsian), which is
P palatine unknown at the main Ukhaa Tolgod expo¬
pat palatine teeth sures. The geology and circumstances of
po postorbitofrontal vertebrate fossil occurrence at Ukhaa Tolgod
pf prefrontal has recently been reviewed by Loope et al.
pmx premaxilla (1998) and Dingus et al. (in press). Basically,
pt pterygoid
vertebrate fossils are most abundant in struc¬
ptt pterygoid teeth
tureless sandstone facies, which have been
sptm septomaxilla
interpreted as alluvial flows from catastroph¬
t tooth
ically collapsing semistable sand dunes.
V vomer
vplf ventral posterior lacrimal foramen Structural collapse was due to saturation of
the dune. Several different alluvial flows have
been identified at Ukhaa Tolgod, and this
GEOLOGICAL OCCURRENCE
model has now been extended to Bayn Dzak
IGM 3/767 was collected at the Little (Dashzeveg et al., 2005). In many cases the
Ukhaa locality (Dingus et al., in press; remarkable preservation of specimens from
Makovicky et al., 2003), Omnogov Aimag, Ukhaa Tolgod suggests that the animals were
Mongolia, during the 2001 Mongolian buried alive.
Academy of Sciences-American Museum of The age of the Ukhaa Tolgod fossil beds
Natural History Paleontological Expedition. is not readily apparent. However, estimates
Little Ukhaa lies approximately 10 kilome¬ based on faunal similarity to Bayn Dzak
ters west of the main exposures at Ukhaa suggest a Campanian age (Dingus et al., in
Tolgod. The Little Ukhaa locality was dis¬ press).
2008 NORELL ET AL.: NEW GOBI PLATYNOTAN 3
Fig. 2. The locality of Little Ukhaa showing its relationship to the main exposures at Ukhaa Tolgod,
Omnogov, Mongolia.
SYSTEMATIC PALEONTOLOGY navigational aids along old caravan routes
and, more recently, roads. Ovoos are venerat¬
SQUAMATA OPPEL, 1811 ed by Mongols and are worshipped by circling
ANGUIMORPHA FURBRINGER, 1900 them clockwise three times and adding offer¬
PLATYNOTA CAMP, 1923
ings in the form of rocks, prayer-flags, money
VARANOIDEA CAMP, 1923
and even vodka bottles. Gurvel- derives from
Ovoo guvvel, new taxon the Mongolian word for lizard.
Type locality and horizon: Little Ukhaa
Holotype specimen: IGM 3/767, well-pre¬ Tolgod Nemegt Basin, Mongolian Gobi
served partial skull with the braincase and Desert; Upper Cretaceous Djadokhta Forma¬
mandibles missing. tion (Loope et al., 1998).
Etymology: Ovoo- is from Mongolian Known distribution: Known only from
ovoo (pronunciation: o-boe), meaning “a heap the type locality and horizon.
or cairn” (fig. 3). A remnant of the pre- Diagnosis: Distinguished from Chermino-
Buddhist religion of Mongolia, these cairns tus longifrons and other closely related var-
are said to be inhabited by local spirits. anoids by the following character states: nasals
Occasionally they are also way points and paired; presence of aperture between premaxilla
4 AMERICAN MUSEUM NOVITATES NO. 3605
Fig. 3. A Mongolian ovoo at the spring of Naraan Bulag in the Nemegt Basin, Omnogov, Mongolia. 43°
27.891N 104° 57.84W
and maxilla (the premaxillary fenestra sensu Premaxilla: The premaxillae are fused as
Gauthier, 1982; see also Gao and Norell, 1998); a single element to form the anterior terminus
anteromedial process of maxilla separating of the snout. The nasal process is flat and
premaxilla from septomaxilla; dorsal septomax- straplike, and attenuates posteriorly as it
illary foramen strongly reduced and close to divides the paired nasals by one half of the
midline (from Gao and Norell, 2000). length of the process. Tiny posterior premax¬
Sharing with Aiolosaurus oriens character illary foramina (anterior ethmoidal openings)
states including presence of a premaxilla- are developed at the base of the nasal process.
maxilla aperture; dorsal septomaxillary fora¬ The tooth-bearing base of the premaxilla has a
men strongly reduced and close to midline. well-developed posterior shelf that forms an
Distinguished from Aiolosaurus oriens and extensive subnarial floor ventral to the nasal
other closely related varanoids by the follow¬ process. The posterolateral border of the shelf
ing derived character states: presence of paired is notched for the larger and rounded aperture
mystery bones roofing the nasal/frontal su¬ between the premaxilla and maxilla, and the
ture; absence of dermal sculpturing on the premaxilla contacts the maxilla at a loose
skull bones (region unpreserved in Aiolosaurus fitting joint by its processes medial and lateral
oriens); premaxillary nasal process broader to the aperture. On the palate, a pair of short
than deep; premaxilla-maxilla aperture large vomeromaxillary processes underlie the paired
and rounded; premaxillary teeth 12 (as op¬ vomers. Adjacent to this contact is a single
posed to 7 in Aiolosaurus oriens); maxillary bilobate incisive process (fig. 4C). No ventral
teeth 12-13 (Aiolosaurus oriens 10 at most). premaxillary foramina are observed; however,
they may be obscured by replacement teeth.
DESCRIPTION The fused premaxillae carry a total of 12 tooth
positions, including seven functional teeth and
IGM 3/767 is composed of a rostrum and empty spaces for five others. Eight replace¬
anterior postorbital region (fig. 4). The ante¬ ment teeth are present at the bases of the
rior wall of the orbit is preserved and the functional teeth. This number of the premax¬
frontal is preserved to its contact with the illary teeth is significantly different from that
parietal. Much of the suborbital bar is present, in Aiolosaurus oriens, which has a total of
as is the left postorbital. Most of the palate is seven teeth from the type and only known
preserved in articulation, with vomers, ecto- specimen (Gao and Norell, 2000). The teeth
pterygoids, and palatines preserved. are small, conical, and strongly recurved. The
2008 NORELL ET AL.: NEW GOBI PLATYNOTAN 5
premaxillary teeth are narrow laterally but the retracted naris, allowing a short contact of
slightly expanded labiolingually. the nasal with the maxilla. The lateral border
Septomaxilla: As in other varanoids, the of the mystery bone has a long sutural contact
septomaxillae are only visible in dorsal view. with the prefrontal, and this suture extends to
Together they form much of the floor of the the midlevel of the orbit. The medial border of
narial chamber. Each septomaxilla is bulbous the bone gradually curves posterolaterally
and is supported ventrally by the vomer and from the midline, so that the bony plate is
contacts the maxilla laterally. Medially a small more or less triangular in shape with a short
ridge contacts the nasals just posterior to the and rounded posterior process. Symmetry and
nasal-premaxillary contact. Small dorsal sep- the topological relationship of these structures
tomaxillary foramina are present anteriorly in with the surrounding bones testify to their
anteriorly projected troughs near the midline, identity as actual structures, not artifacts of
lateral to the midline ridge. preservation. To our knowledge, they have no
Nasal: The paired, elongate nasals define known homolog among squamates or any
the medial and posterior borders of the large other vertebrate clade.
retracted nares. Anteriorly, the tapering pro¬ Frontal: The paired frontals are sub-
cess of the nasal extends to a point along the equal to the nasals in length. The dorsal
contact with the nasal process of the premax¬ surface of each bone is essentially smooth but
illa. The anterior process is roughly one half is weakly ornamented with small longitudinal
the length of the entire nasal bone. The narial bumps and ridges along the posterior border.
border is crescentic but lacks anterolateral These appear to be related to the articular
processes, and laterally the nasals have slight surface rather than dermal rugosities. A row
contact with the maxillae just posterior to the of tiny irregular foramina extends from the
posterior corner of the nares. The lateral midline anteriorly to adjacent to the orbital
borders of the widened posterior halves of margin more posteriorly. The anterior third of
the nasals have short sutural contacts with the the frontal is covered by the mystery bone, but
maxillae, but most of the lateral borders as exposed on the right side, the frontal is
contacts the slender processes of paired anteriorly notched and slightly underlies the
mystery bones. As shown on the right side of posterior border of the nasal beneath the
the specimen, the posterior edge of the nasals mystery bone. The lateral border of the frontal
overlaps the frontals beneath the “mystery contacts the elongate supraorbital process of
bones” (fig. 5). the prefrontal along a longitudinal suture. For
“Mystery bones”: The “mystery bones” most of their length the lateral borders of the
are a pair of roofing elements otherwise frontals are parallel sided; posteriorly, howev¬
unknown among squamates. The paired mys¬ er, the borders curve laterally at the back of
tery bones overlie both the nasals and the the orbit to form postorbital processes. The
frontals between the supraorbital processes of posterior third of the right frontal is broken
the prefrontals (fig. 5). This point is important and missing, but the left frontal is preserved to
because the nasals invariably overlie the the simple and transverse frontal/parietal
frontal in squamates. Thus, the preserved suture. The ventral surface is exposed enough
condition demonstrates that the mystery to show the presence of extensive subolfactory
bones are distinct from the anterior portions processes (= cristae cranii, or frontal down-
of the frontals that they overlie. They do not growths), which meet at the midline as in
have any characteristics of osteoderms and are extant Varanus. No bones of the skull table
therefore neomorphic ossifications of the skull except for the postorbital (see below) are
roof. The paired bones are relatively small thin preserved posterior to the frontals.
plates, with a short midline suture contact. Maxilla: The subtriangular maxilla forms
Anteriorly, each bone is bifurcated with a most of the lateral surface of the rostrum. The
short anteromedial process along the midline, nasal process of the maxilla is low and not
and a much longer anterolateral process distinctly offset from the narial margin, such
extending between the nasal and the prefron¬ that the dorsal margin is a gentle, oblique
tal. However, the latter process failed to reach incline in lateral view. The lateral surface of
6 AMERICAN MUSEUM NOVITATES NO. 3605
Fig. 4. A) The holotype skull of Ovoo gurval in A, ventral, B, dorsal, C, left lateral, and D, right
lateral views.
the maxilla shows a slightly impressed fossa process behind premaxillary nasal process.
posteriorly, bounded ventrally by the dental The narial margin starts anteriorly as a
margin. A row of labial foramina (exits for the rounded ridge that becomes sharper and more
ethmoidal nerves and for labial blood vessels) medially curved posteriorly. Inside the narial
parallels the dental border. In dorsal view, the chamber lie the well-ossified septomaxillae
bone is anteriorly forked with well-developed (see below), and lateral to the septomaxilla/
anterolateral (premaxillary) and anteromedial maxilla contact is the anterior opening of the
(septomaxillary) processes. Between these two superior alveolar canal on the inner wall of the
anterior processes is a narial fossa and the maxillary bone. The maxilla broadly overlaps
semicircular notch for the large and rounded the anterolateral surface of the prefrontal. The
premaxillary aperture. The anteromedial pro¬ posterior suture between the nasal process and
cess is anteroposteriorly short, but is medially the prefrontal runs posterolaterally from the
elongate such that it contacts the opposite posterior terminus of the naris to the anterior
2008 NORELL ET AL.: NEW GOBI PLATYNOTAN 7
Fig. 4. Continued.
extremity of the orbit, where the maxilla al canal (maxillopalatine foramen) lies near
contacts the small lacrimal (see below). The this suture adjacent to the space between the
posterior process of the maxilla tapers pos- penultimate and ultimate tooth. This opening
teroventrally. It contacts the lacrimal on the of the infraorbital canal is most apparent on
ventral surface of the latter, and lies on the the left side, but it can also be observed on the
lateral surface of the common contact between right side.
the palatine and ectopterygoid. The palatine- The maxillary teeth have bases that are
ectopterygoid contact occurs in about the expanded anterodorsally and compressed lat¬
anterior quarter of the orbit just posterior to erally. The maxilla carries no more than 13
the last maxillary tooth. Contact with the teeth for the complete tooth row; the left side
ectopterygoid is preserved on the left side of shows 10 well-preserved teeth and the spaces
the skull and is a complex kinetic joint where for two to three others, and the right side has
the ectopterygoid fits into a socket formed by eight functional teeth and four to five empty
the maxilla ventrally and the palatine dorsally. spaces. The largest teeth are located anteriorly
On the palatal surface, the maxillary teeth and in the middle portion of the tooth row,
are supported by a narrow dental shelf, which with posterior teeth progressively smaller. The
borders the elongate internal choana. The maxillary teeth show weakly developed, but
dental shelf expands slightly medially posteri¬ clearly defined infoldings at the tooth base.
orly, reaching its widest point at the contact These are interpreted as plicidentine, a char¬
with the anterior terminus of the anterior acteristic of extant varanoids (see Zaher and
maxillary process of the palatine. Posteriorly it Rieppel, 1999, and Rieppel et al., 2003, for a
contacts the palatine along a diagonal, later¬ discussion of this character). Along the
ally directed suture, which causes the skull to maxillary tooth row he several smaller re¬
flare laterally at the anterior corner of the placement teeth at the base of the functional
orbit. The posterior opening of the infraorbit¬ teeth, and these replacement teeth are approx-
AMERICAN MUSEUM NOYITATES NO. 3605
Fig. 6. The left anterior orbital wall.
A fragment of the postfrontal portion of the
left postorbitofrontal is preserved adjacent to
the frontal. The slender and elongate posterior
process of the postorbital is completely
preserved on the left side, and this process is
still in articulation with the broken anterior
process of the squamosal, demonstrating the
imately half the size of, or even smaller than, presence of a complete supratemporal arch in
the functional teeth. The teeth show well- this taxon. The anterior process (the frontal
developed resorption pits. process of the postfrontal) of the postorbital
Prefrontal: The large prefrontal lies be¬ bone is broken, but the articular groove along
tween the retracted nares and the orbits, and the lateral edge of the frontal indicates the
forms most of the anterior wall of the orbit. presence of the prefrontal/postorbitofrontal
The frontal process of the prefrontal extends contact as in some varanoids (e.g.,
posteriorly to form most of the dorsal margin Cherminotus longifrons, Lanthanotus borneen-
of the orbit. Although no contact is preserved sis, and Varanus prisca). The ventrolateral
between the prefrontal and the anterior process process of the postorbitofrontal is smooth,
of the postorbitofrontal, a well-developed showing no indication of possible articulation
articular groove along the lateral edge of the with the (missing) jugal.
frontals indicates that such a contact is present Lacrimal and Posterior Lacrimal
excluding the frontal from participation in the Foramina: The lacrimal is nearly completely
orbital margin. The orbital process of the preserved on the right side of the skull but is
prefrontal contacts the palatine in a broad fragmentary on the left. It is a small element,
suture that runs perpendicular to the long axis fitting in the anterior corner of the orbit, and
of the skull for most of its length, but is contributes only to the lateral wall of the
ventrolaterally directed near the lateral margin single lacrimal foramen (fig. 6). There is no
and extends posteriorly toward the jugal pronounced, posterior flange like that seen in
ventral to the lacrimal. The medial edge of this extant Varanus. The posterior lacrimal foram¬
downward extension forms the lateral border ina are paired as in extant Varanus (see Norell
of the orbitonasal fenestra and its lateral edge is et al., 1992: fig. 10). The dorsal posterior
notched to form the medial border of the dorsal lacrimal foramen is relatively small, and opens
posterior lacrimal foramen (fig. 6). between the prefrontal and the lacrimal, rather
Postorbitofrontal: The postorbital and than penetrating the latter bone as in
postfrontal are, apparently, fused in this taxon Lanthanotus borneensis. The ventral posterior
as they are in many extant Varanus, in lacrimal foramen is small and completely
contrast to the condition seen in the Eocene enclosed in the lacrimal. The jugal is not
Saniwa ensidens (Rieppel and Grande, 2007). preserved on either side of the skull, but an
2008 NORELL ET AL.: NEW GOBI PLATYNOTAN 9
articular surface on the left ectopterygoid and slightly more than half of the medial boundary
a broken surface on the posterodorsal surface of the suborbital fenestra. The pterygoid
of the maxilla indicate its original presence in contacts the palatine mostly medially where
this taxon. there is a groove to receive an anterolateral
Vomer: The vomers are paired, greatly flange on the pterygoid. The pterygoid process
elongate and straplike, parallel-sided elements and posterior/posterolateral margins of the
that lie adjacent to the midline of the palate. maxillary process forms the anterior, and
Anteriorly they contact the premaxilla and anteromedial boundary, of the suborbital
maxilla, and posteriorly they extend to contact fenestra. Anteriorly a small medial oblique
the palatine at the level of the penultimate surface projects into the pterygoid fenestra. A
posterior maxillary tooth. Their lateral surface row of at least four small, conical, recurved
forms the entire medial boundary of the palatine teeth are present beginning at the
internal choana (fenestra exochoanalis). posterior margin of the palatine and extending
Anteriorly there is a small emargination just forward (palatine teeth are lost in Varanus
posterior to the contact with the maxilla, but are retained in some specimens of
which presumably is the anterior opening for Lanthanotus, but see McDowell and Bogert,
Jacobson’s organ (fenestra vomeronasalis ex¬ 1954; Jollie, 1960; Rieppel, 1980a).
terna). Anteriorly the vomers meet and form a Pterygoid: The pterygoids are paired
narrow fossa on the midline. At the anterior sinuous Y-shaped bones. Only the left ptery¬
end of this fossa lies a pair of anteriorly goid is well preserved. The ectopterygoid
projected vomero-premaxillary foramina. The process is splintlike and fits into a deep laterally
vomers are in medial contact for only about projected slot on the ectopterygoid. The
half their length, being posteriorly separated laterally exposed surface of the pterygoid is
by the so-called interpterygoid vacuity (or dorsoventrally concave. On the ventral surface
pyriform recess). Each vomer is L-shaped in the ectopterygoid ramus is very short and
cross-section. At their common anterior con¬ forms none of the lateral border of the
tact, they form a composite structure shaped suborbital fenestra. The anteromedial (pala¬
like an inverted T in cross-section, where tine) process carries a pair of loosely organized
lateral flanges of bone form extensive vomer¬ tooth rows that are anteriorly confluent with
ine shelves. The vomers are toothless as in the palatine tooth row and that extend
other varanoids generally (but see Eosaniwa posterior to the midlevel between the suborbital
koehni [Rieppel et al., 2007]). fenestra and the basipterygoid process. Like the
Palatine: The palatines are paired, tetra- palatine dentition, the teeth are small but
radiate elements. An anteromedial process of recurved and pointed. A transversely concave
the palatine ventrally overlies the vomer in a fossa laterally parallels this tooth row, origi¬
broad overlapping joint (a scarf joint). A nating just posterior to the level of the
ventral tuberosity is present at the anterior ectopterygoid process and extending posterior¬
margin of the palatine at the overlap with the ly beyond the pterygoid teeth. Just posterior to
vomer. A well-defined exochoanal fossa ex¬ the tooth row, the basipterygoid process
tends along the ventral surface of the palatine, projects medially and the thin, incomplete
but there is no development of a secondary quadrate process extends posterolaterally.
palate. The exochoanal fossa possesses a thin Ectopterygoid: Only the left ectoptery¬
roof divided by a lateral ridge at the posterior goid is completely preserved. It is a stout bone
end as in Lanthanotus borneensis. The anterior that bridges the palatine-maxilla complex with
maxillary process extends as a narrow splint to the pterygoid and forms the entire lateral
the level of the fourth-to-last maxillary tooth. boundary of the suborbital fenestra. In ventral
Along the suture with the maxilla lies a small view, the ectopterygoid arches laterally form¬
ventral opening from a branch of the infraor¬ ing the widest part of the preserved region of
bital canal. As mentioned above, the palatine the skull. The anterior process curves antero-
with the maxilla forms a socket for articula¬ medially to contact the palatine, excluding the
tion with the anterior process of the ectoptery¬ maxilla from the suborbital fenestra. The
goid. The large pterygoid process forms ventral surface of the ectopterygoid is a nearly
10 AMERICAN MUSEUM NOVITATES NO. 3605
flat to slightly concave surface. The ectoptery- recovered 2288 equally short trees. The length
goid is apparently laterally exposed, but the of each tree is 3286 steps and a retention index
dorsolateral surface was almost certainly of 0.7615.
overlain by the jugal (missing from the We report both the strict consensus
specimen; see above). (fig. 7A) and the Adams consensus (fig. 7B)
Palpebral: No palpebral bones were trees as recovered by PAUP* (Swofford,
found associated with IGM 3/767. However, 2001). The Adams consensus collapses volatile
in extant Varanus the palpebral lies in a slitlike taxa to their most basal recovered position
fossa between the lacrimal and the prefrontal and shows relationships that are consistent
near the anterodorsal orbital rim. A well- with ah of the principle trees.
defined fossa matching the Varanus condition Ovoo gurval is recovered as a basal member
is present in the new taxon, suggesting that a of the Varaninae (those taxa closer to Varanus
palpebral may have been present. varius than to Lanthanotus borneensis) in all of
the principal trees recovered in the T.N.T.
PHYLOGENETIC ANALYSIS analysis (fig. 7C-E). Aiolosaurus oriens is
variably recovered as the sister taxon to
Phylogenetic relationships within the Cherminotus longifrons (a derived lanthano-
Varanoidea and, more globally, within the tine; Conrad, in press) (fig. 7C), as the basal-
Platynota have been inferred from several most member of Varaninae (fig. 7D), or as the
semi-independent data sets (McDowell and sister taxon to Ovoo gurval at the base of
Bogert, 1954; Borsuk-Bialynicka, 1983, 1984; Varaninae (fig. 7E). Consequently, the Adams
Pregill et al., 1986; Norell et al., 1992; Norell consensus tree (fig. 7B) shows Ovoo gurval as
and Gao, 1997; Lee, 1997; Lee and Caldwell, the outgroup to Saniwa ensidens and Varanus.
2000; Rieppel, 2000). Recently, Conrad (in In the Adams consensus tree, Varanidae is
press) presented an extensive analysis of supported by five unambiguous synapomor-
squamates based on morphological characters. phies. These are: 3(1), presence of a rounded
We added Ovoo gurval and 28 other taxa snout in dorsal view; 65(0), absence of a
to the data matrix from Conrad (in press), contact between the frontal and maxilla, and
which previously included 222 ingroup 149(1), laterally extensive crista tuberalis;
taxa and 363 morphological characters. The 151(1), spheno-occipital tubercle placed ante¬
added taxa include eight species of Varanus, riorly such that the crista tuberalis is pos-
four recently described mosasaur species, two terodorsally inclined; and 178(0), presence of a
“agamids”, two glyptosaurines, Hymeno- ventrally convex dentary. The unambiguous
saurus clarki, and 11 species-level codings to synapomorphies supporting the clade formed
replace the previously compositely coded by Cherminotus longifrons and Lanthanotus
Iguanidae, Corytophanidae, Crotaphytidae, borneensis in the Adams consensus tree are:
and Phrynosomatidae (see appendix 2). We 32(1), presence of a medially flared palatine
also added 9 new characters to the data flange on the maxilla, and 83(1), presence of a
matrix. Ovoo gurval could be scored for 112 nuchal fossa on the posterodorsal margin of
of the characters included in this new matrix. the parietal. The clade consisting of Ovoo
Character ordering and rationale were derived gurval, Saniwa ensidens, and Varanus is
from Conrad (in press). We also corrected the supported by 27(1), contact of the anterome¬
codings for the Varanus species in that matrix dial processes of the maxilla posteroventral to
to reflect the large contribution of the the premaxillary nasal process; 51(1), absence
prefrontal to the orbitonasal fenestra. We also of a contact between the jugal and postorbito-
changed the coding to reflect the nature of the frontal; and 62(1), presence of a midline
“crawling” sculpturing present on the skull contact of the frontal subolfactory processes.
bones of Aiolosaurus oriens. We analyzed these
data using the computer program T.N.T.
DISCUSSION
using the New Technology Search (1,000
replicates) and three subsequent ratchet repli¬ Ovoo gurval adds importantly to our knowl¬
cates (each of 1,000 replicates). Our analysis edge of Djadoktha Lormation squamates, to