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TAXONOMIC COMPOSITION AND SYSTEMATICS OF LATE ASSEMBLAGES FROM UKHAA TOLGOD AND ADJACENT LOCALITIES, MONGOLIAN GOBI

GAO KEQIN Frick Research Fellow, Division of American Museum of Natural History

MARK A. NORELL Chairman and Associate Curator, Division of Paleontology American Museum of Natural History

BULLETIN OF THE AMERICAN MUSEUM OF NATURAL HISTORY Number 249, 118 pages, 37 ®gures, 1 table, 1 appendix Issued March 24, 2000 Price: $11.30 a copy

Copyright ᭧ American Museum of Natural History 2000 ISSN 0003-0090 CONTENTS Abstract ...... 4 Introduction ...... 4 Geological Setting ...... 5 Systematic Paleontology ...... 11 Oppel, 1811 ...... 11 Iguania Cope, 1864 ...... 11 (sensu lato: nonacrodontan iguanians) ...... 11 Ctenomastax parva, new and ...... 11 Temujinia ellisoni, new genus and species ...... 18 Zapsosaurus sceliphros, new genus and species ...... 25 Polrussia mongoliensis Borsuk-Bialynicka and Alifanov, 1991 ...... 31 Cope, 1864 ...... 32 crassus Gilmore, 1943 ...... 32 Priscagama gobiensis Borsuk-Bialynicka and Moody, 1984 ...... 34 Phrynosomimus asper Alifanov, 1996 ...... 36 Iguania Incertae sedis ...... 40 Isodontosaurus gracilis Gilmore, 1943 ...... 40 Cuvier, 1817 ...... 46 Family Incertae sedis ...... 47 Myrmecodaptria microphagosa, new genus and species ...... 47 Camp, 1923 ...... 52 Gray, 1827 ...... 52 Adamisaurus magnidentatus Sulimski, 1972 ...... 53 Gobinatus arenosus Alifanov, 1993 ...... 55 Tchingisaurus multivagus Alifanov, 1993 ...... 62 Pyramicephalosaurus cherminicus Alifanov, 1988 ...... 66 Macrocephalosaurus Gilmore, 1943 ...... 70 Macrocephalosaurus sp...... 70 Macrocephalosaurus chulsanensis Sulimski, 1975 ...... 70 Erdenetesaurus robinsonae Sulimski, 1975 ...... 72 Cherminsaurus kozlowskii Sulimski, 1975 ...... 73 ?Scincoidea Oppel, 1811 ...... 74 Parmeosaurus scutatus, new genus and species ...... 74 Hymenosaurus clarki, new genus and species ...... 79 Scincomorpha Incertae sedis ...... 82 New genus and species (unnamed) ...... 82 Slavoia darevskii Sulimski, 1984 ...... 86 Globaura venusta Borsuk-Bialynicka, 1988 ...... 86 Eoxanta lacertifrons Borsuk-Bialynicka, 1988 ...... 89 FuÈrbringer, 1900 ...... 90 Carusioidea Gao and Norell, 1998 ...... 90 Carusiidae Borsuk-Bialynicka, 1987 ...... 90 intermedia Borsuk-Bialynicka, 1985 ...... 90 Camp, 1923 ...... 92 Monstersauria Norell and Gao, 1997 ...... 92 Gobiderma pulchrum Borsuk-Bialynicka, 1984 ...... 93 mongoliensis Norell et al., 1992 ...... 94 Camp, 1923 ...... 95 Cherminotus longifrons Borsuk-Bialynicka, 1984 ...... 95 Aiolosaurus oriens, new genus and species ...... 97 Varanoidea, genus and species undetermined ...... 100 2 2000 GAO AND NORELL: FROM MONGOLIA 3

Taxonomic Diversity, Phylogenetic Signi®cance, and Stratigraphic Distribution of the Lizard Assemblage ...... 100 Paleoecology and Mode of Specimen Preservation ...... 105 Conclusions ...... 107 Acknowledgments ...... 108 References ...... 108 Appendix 1 ...... 115 4 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249

ABSTRACT Upper Cretaceous deposits at Ukhaa Tolgod and adjacent localities in the Mongolian Gobi Desert have yielded a large number of superbly preserved lizard specimens, including repre- sentatives of several new taxa (described in this paper) and important supplementary material of several previously poorly known taxa. Study of these specimens gives important insight into the taxonomic diversity and systematics of the Late Cretaceous lizard fauna of the Gobi Desert. A preliminary survey indicates that the lizard assemblage from Ukhaa Tolgod and adjacent localities consists of some 30 species in four higher groups (Iguania, Gekkota, Scin- comorpha, and Anguimorpha). The iguanians are documented by eight species, including three species newly recognized in this paper. The Scincomorpha are the most diverse group, rep- resented by as many as 14 species including three new and 11 previously known species. The Anguimorpha are nearly as diverse as the Iguania, while the Gekkota is the least diverse group with a single species documented in the assemblage. The scincomorphs include forms that are highly specialized for burrowing life-styles, interpreted from their cranial morphology as pos- sibly analogous to extant species. The anguimorphs include phylogenetically important members of several major anguimorph . The paleoecological signi®cance of these lizards cannot be overlooked. According to morphology, most lizards are predatory in terms of habit, while true herbivorous species are rare. Most specimens are preserved as articulated with , but virtually complete skeletons in situ are quite common. Delicate parts of the , such as the braincase and ear ossicles, are undistorted and the surfaces of the bones show no sign of sand abrasion. These observations indicate not only relatively quick burial but also burial under relatively mesic climatic conditions with low-energy water involved during the taphonomic process.

INTRODUCTION During the past few , the Mongolian beds are Djadokhta equivalents. The dino- Academy of Science±American Museum of saur and assemblages show both Natural History Expeditions made extraor- Djadokhta and Barun Goyot af®nities (No- dinary collections from a remarkably rell, 1997b; Dashzeveg et al., 1995). productive locality named Ukhaa Tolgod in Most of the specimens are superbly pre- the Nemegt Basin, southwestern Gobi Desert served skulls with mandibles. Some have ar- (®g. 1), Mongolia. Ukhaa Tolgod is part of a ticulated postcranial skeletons. The majority suite of localities throughout the Gobi Desert of lizard specimens were collected in struc- that display a characteristic fauna (Dashzev- tureless or vaguely cross-bedded, ®ne to eg et al., 1995). Most of these are in the Dja- coarse sandstones. These sediments are in- dokhta and Barun Goyot formations. The terpreted as originating from alluvial fans Djadokhta Formation has been considered that were built from dune sands at the mar- mid-, and the Barun Goyot late gins of stabilized bedforms during mesic cli- Campanian in age (Fox, 1978; Lillegraven matic episodes (Loope et al., 1998). The sur- and McKenna, 1986; Jerzykiewicz et al., faces of the bones show no sand abrasion as 1993). However, recent work in Kazakhstan is common in elements preserved in typical suggests an early Campanian age for the Dja- eolian deposits. This exquisite preservation dokhta Formation (Averianov, 1997). Be- and extraordinary concentration of sides signi®cant mammal and fos- specimens is characteristic of Ukhaa Tolgod sils, Ukhaa Tolgod has yielded some 1000 when compared to other localities within the lizard specimens. This is the largest collec- Cretaceous series of the Gobi Desert. tion of fossil lizards ever collected from a The purposes of this paper are to describe single locality within the Gobi Desert. Cor- and diagnose several new lizard taxa, to pro- relation of Ukhaa Tolgod with Djadokhta and vide an overview of the taxonomic diversity Barun Goyot sections is not unambiguous of lizards from Ukhaa Tolgod, and to com- (see e.g., Dashzeveg et al., 1995), but Loope pare this with the fauna of other Djadokhta et al. (1998) hinted that the Ukhaa Tolgod and Barun Goyot localities. As lizards are 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 5 sensitive environmental indicators (Greene, tion; IGM, Institute of Geology, Mongolian 1982; Pianka, 1986), these specimens allow Academy of Sciences, Ulaanbaatar, Mongo- preliminary comment to be made regarding lia; IVPP, Institute of Vertebrate Paleontol- the environment in which they lived. Most ogy and Paleoanthropology, Beijing, China; of the specimens described in this paper are MAE, Mongolian Academy of Sciences± from the Ukhaa Tolgod locality. In addition, American Museum of Natural History Ex- specimens from other localities such as Tug- peditions, ®eld numbers; PIN, Paleontologi- rugeen Shireh, Khulsan, and Zos are includ- cal Institute, Academia Nauk, Moscow, Rus- ed, because they provide material for recog- sia; ZPAL, Palaeobiological Institute, Polish nition of new lizard taxa, supplementary data Academy of Sciences, Warsaw, Poland. for a better understanding of previously Abbreviations used in the ®gures: an, an- known taxa, and additions to faunal lists gular; an proc, angular process; cor compiled for these localities. These localities emarg, anterior coracoid emargination; asaf, are brie¯y described below. anterior surangular foramen; bo, basioccipi- Throughout this paper the general taxo- tal; bs, basisphenoid; cap, capitellum; cl, nomic framework follows that proposed by ; cor, coronoid; cora, coracoid; cora Estes (1983), Estes et al. (1988), and Frost for, coracoid foramen; den, dentary; ect, ec- and Etheridge (1989) with modi®cations as topterygoid; ecte, ectepicondyle; ente, ente- picondyle; ept, epipterygoid; fr, frontal; hu, explained in the text. The intent of this paper humerus; ju, jugal; la, lacrimal; liaf, lateral is to describe these lizard specimens and, in inferior alveolar foramina; lsaf, lateral su- cases where new taxa are discussed, to pro- perior alveolar foramina; max, ; msc vide diagnoses. It is outside the scope of this proc, mesoscapular process; na, nasal; oc paper to provide an explicit phylogenetic hy- cond, occipital condyle; pa, parietal; paf, pa- pothesis for all of the taxa included here. rietal foramen; pal, palatine; palp, palpebral; This work is ongoing (Norell and Gao, 1997; pf, postfrontal; pm, premaxilla; po, postor- Gao and Norell, 1998), and it is hoped that bital; pof, postorbitofrontal; prart, prearti- this paper will inspire work on this collec- cular; prcor proc, procoracoid process; prf, tion. prefrontal; psaf, posterior surangular fora- Institutional abbreviations: AMNH, men; ptg, pterygoid; qu, quadrate; sa, sur- American Museum of Natural History, New angular; sc, ; spl, splenial; sq, squa- York; AMNH-DVP-CA, American Museum mosal; supoc, supraoccipital; supt, supra- of Natural History, Department of Vertebrate temporal; supt fene, supratemporal fenestra; Paleontology comparative collec- troch, trochlea; vom, vomer.

GEOLOGICAL SETTING The fossiliferous Late Cretaceous red and Ukhaa Tolgod (®g. 1). Collectively, these are white sandstones of Mongolia and northern called the Djadokhta-like or protoceratopsian China have been known for over 75 years beds (Norell et al., 1996). On the basis of (Andrews, 1932). However, even though sev- fauna and lithology, two separate formations eral international expeditions have made im- are recognized (see Gradzinski et al., 1977): portant collections in these deposits (see La- the Djadokhta (the localities of Bayn Dzak, vas, 1993; Dong, 1993; Novacek, 1996; Kie- Tugrugeen Shireh, Bayan Mandahu, and lan-Jaworowska, 1969), relatively little is Udan Sayr), and the Barun Goyot (the local- known concerning their age, origin, and in- ities of Khulsan and Khermeen Tsav). The terrelationships. two geological formations are regarded as The best known of these localities are mid- and late Campanian in age, respectively Bayn Dzak (the Flaming Cliffs), Udan Sayr, (see above). Bayan Mandahu, Khermeen Tsav, Khulsan, Ukhaa Tolgod is from an unde®ned unit; Alag Teg, the Monadonocks, Tugrugeen Shi- however, it has been suggested that it has reh, and the focus of most of this report, strong Djadokhta similarities (Loope et al., 6 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249

Fig. 1. Map of Mongolian Gobi Desert showing major fossil localities.

1998). Detailed reviews of many of these lo- Djadokhta locality to be discovered and is calities (some with con¯icting interpretations the locality of the Djadokhta Formation of sedimentary history) can be found in Ber- (Berkey and Morris, 1927). It was found dur- key and Morris (1927); Gradzinski et al. ing the ®nal day of the 1922 segment of the (1968), Gradzinski et al. (1977); Jerzykiew- American Museum of Natural History's Cen- icz et al. (1993); Lefeld (1971); Eberth tral Asiatic Expeditions (Andrews, 1932; No- (1993); Gradzinski and Jerzykiewicz (1972, rell, 1997a). Parties returned there on sub- 1974a, 1974b). Faunal lists for many of the sequent years and made large collections. localities are given in these papers as well as The locality (®g. 2) consists of an extensive notably in several other papers (Jerzykiewicz cliff face with small badlands and outlying and Russell, 1991; Dashzeveg et al., 1995; outcrops at its base. The name ``Flaming Kielan-Jaworowska, 1974; OsmoÂlska, 1980; Borsuk-Bialynicka, 1991b). These lists are Cliffs'' was inspired by the color of the sed- badly in need of revision to re¯ect discov- iments which at sunset glow with a brilliant eries over the last decade. Fossil lizard oc- red-orange color (see Novacek et al., 1994). currences at these localities are discussed in Remains of Protoceratops andrewsi are a later section (stratigraphic distribution). A extremely common. Eggs and nests are also brief description of each of the localities re- regularly encountered. Other are ferred to in this paper is given below. found with less frequency, and these include the typical ``Djadokhta fauna'' of Pinacosau- DJADOKHTA LOCALITIES rus grangeri, and rare theropods like velo- Bayn Dzak ciraptorine dromaeosaurs, oviraptorids, and troodontids (Jerzykiewicz and Russell, Commonly called the ``Flaming Cliffs,'' 1991). Remains of mononykine alvarezsaur- Bayn Dzak (Shabarakh Usu) was the ®rst ids (Norell et al., 1993), and a variety of tur- 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 7

Fig. 2. Landscape of the Gobi localities. Top photo: view of the Flaming Cliffs (the classic locality Bayn Dzak); bottom photo: the new fossil bonanza, Ukhaa Tolgod. tles (Gilmore, 1931) and crocodiles (OsmoÂl- this locality. These include ®ve taxa de- ska, 1972) have also been collected. Occa- scribed by Gilmore (1943): Macrocephalo- sionally, extremely fragmentary specimens saurus ferrugenous, Conicodontosaurus dja- of large dinosaurs are also encountered. dochtaensis, Mimeosaurus crassus, Isodon- Large collections of mammal (both therians tosaurus gracilis, and Telmasaurus grangeri. and nontherians) and lizard specimens have Later discoveries added six more taxa: Pris- also been made here by American, Polish, cagama gobiensis, Bainguis parvus, Adami- Mongolian, Russian, and Mongolian-Ameri- saurus magnidentatus, Globaura venusta, can expeditions (Lavas, 1993). Carusia intermedia, and Estesia mongolien- A total of 11 lizard taxa are recorded from sis (see later sections in this paper). 8 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249

The depositional regime at the Flaming with small like therian and nonther- Cliffs has generally been determined to rep- ian and lizards. resent eolian deposition with some ¯uvial Tugrugeen Shireh preserves in spec- component, although the sedimentology of tacular fashion, perhaps allowing behaviors to this locality is currently under review by be estimated. For example, the ``®ghting di- Dingus and Loope (personal commun.). In nosaurs'' have been interpreted as indicative places there is an extensive , as of animals overcome in the heat of battle evidenced by root casts and bore holes (Le- (contra OsmoÂlska, 1993), whereas death as- feld, 1971). semblages of Protoceratops andrewsi, all ori- ented in the same direction, may indicate Chimney Buttes some behavior of these animals in response to wind direction (Fastovsky et al., 1997). During the 1993 Mongolian Academy of This phenomenon is also documented at Bay- Sciences±American Museum of Natural His- an Mandahu (Jerzykiewicz et al., 1993). tory expeditions to the Gobi Desert, a small Lizard specimens collected from this lo- exposure was visited between the town of cality are referred to nine taxa. These include Bulgan and the Bayn Dzak locality. Dash- Isodontosaurus gracilis, Flaviagama dzer- zeveg suggested that the locality be called zhinskii, Adamisaurus magnidentatus, Mi- Chimney Buttes. This exposure is extremely meosaurus tugrikinensis (see later com- small; however, a few signi®cant specimens ments), two new iguanians described in this were found there including an articulated paper, Cherminotus longifrons (see later sec- skeleton of Velociraptor mongoliensis (No- tion for details), Dzhadochtosaurus gigan- rell and Makovicky, 1999). Other typical teus, and Gurvansaurus canaliculatus (see Djadokhta-like taxa were recovered as well, Alifanov, 1996). including oviraptorid-type eggs and adults and juveniles of Protoceratops andrewsi. Multituberculate and lizard specimens were Bayan Mandahu found in small concretions. Bayan Mandahu (®g. 1) in north central Although extremely close to the locality of China is the only Djadokhta-like locality that Tugrugeen Shireh, lithologically Chimney has yielded signi®cant collections outside of Buttes more closely resembles the Flaming Mongolia. It is placed in the Djadokhta For- Cliffs in that the rocks are bright red in color mation on the basis of lithology and a com- and extremely ®ne grained. To date, no de- mon fauna (Jerzykiewicz et al., 1993). The tailed geologic work has been done at this site. Late Cretaceous beds in the nearby area (Bayan Tu) were ®rst reported by the Amer- Tugrugeen Shireh (Tugrikin-Shireh) ican Museum of Natural History Central Asi- Also in the general area of Bayn Dzak, lies atic Expeditions (Spock, 1930: Go Yoto For- Tugrugeen Shireh, a locality probably most mation), and later by Sino-Swedish expedi- famous for the discovery of the ®ghting di- tions (see Bohlin, 1953). The Bayan Man- nosaurs (a Velociraptor and a Protoceratops dahu locality was discovered and extensively locked in mortal combat; see Jerzykiewicz et sampled by paleontologists of the Sino-Ca- al., 1993: ®g. 11; see also OsmoÂlska, 1993 nadian Dinosaur expeditions during the years for different interpretations). Unlike the 1986±1990 (see Currie, 1993; Dong, 1993). Flaming Cliffs, the sands of Tugrugeen Shi- Lizard collections from this locality belong reh are brilliant white to tan in color, and are to 17 genera in eight families. These were considered to be the result of eolian deposi- described by Gao and Hou (1996). tion (Fastovsky et al., 1997). Although Bayan Mandahu shows many The dinosaur fauna of Tugrugeen Shireh is faunal similarities to the Djadokhta, it also classically Djadokhta (see Jerzykiewicz and shows similarities with the Barun Goyot For- Russell, 1991); specimens of Protoceratops mation and is aberrant in yet other aspects. andrewsi are abundant, and Velociraptor For instance, the protoceratopsian fauna of mongoliensis elements (see Norell and Ma- Bayan Mandahu may contain all three Dja- kovicky, 1997, 1999) commonly occur along dokhta protoceratopsians (i.e., Protoceratops 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 9 andrewsi, Bagaceratops rozhdestvenskyi, and were recovered including several ovirapto- Udanoceratops tschizhovi). Jerzykiewicz et rids, some represented by embryos and al. (1993) were, however, tentative in their adults on nests (Norell et al., 1994; Norell et identi®cations of these taxa beyond Proto- al., 1995). Nearly 500 mammal specimens ceratops andrewsi, and more detailed study were discovered, along with a thousand liz- needs to take place before we can de®nitively ards (Gao and Norell, 1996). The fauna indicate that all three of these taxa are pres- shows strong Djadokhta similarities in that ent at Bayan Mandahu (P. J. Currie, personal Protoceratops andrewsi and Pinacosaurus commun., 1998). (Brinkman and grangeri are common. Several mononykine Peng, 1993), mammals, and crocodilians alvarezsaurids (Chiappe et al., 1998), dro- were also recovered. Curiously, mononykine maeosaurids, and troodontids were also alvarezsaurids are completely missing, and found (Norell et al., 1996). Occasional foot- elements of the lizard fauna are also slightly prints can be seen in cross-section on some different from other Djadokhta localities (see exposures (Loope et al., 1998: ®g. 3b). later discussion). Deposition of fossils at Ukhaa Tolgod was The environment of Bayan Mandahu ap- studied by Loope et al. (1998). These authors parently had more of an eolian component show that the fossiliferous sediments that than any other Djadokhta-like site studied were initially interpreted as predominately thus far, except for perhaps Tugrugeen Shi- eolian sediments (Novacek et al., 1994; reh. Like the latter locality, protoceratopsians Dashzeveg et al., 1995) are in fact strata are found in death assemblages sometimes formed by runoff ¯owing from sand dunes buried in an almost vertical pose (Jerzykiew- during heavy rainstorms. These low-energy runoff ¯ows covered dead or dying animals icz et al., 1993: ®g. 12). Mass mortality sites and buried others in their burrows. This sort of Pinacosaurus grangeri are also found in of deposition is novel for Djadokhta-like sand-dune deposits. rocks. Currently this work is being extended to some of the other localities to see if this Udan Sayr model applies elsewhere (L. Dingus, person- Udan Sayr is a small locality to the north al commun., 1998). of the Barun Saichan Uul. It has yielded a small assemblage including the large proto- Zos ceratopsian Udanoceratops tschizhovi (Kur- Zos is a small locality that is adjacent to zanov, 1992). This locality was visited by the Ukhaa Tolgod; it is a system of ravines that MAE in 1995, 1996, and 1997. Several lizard run into a canyon through the Gilbent Ul. and mammal specimens were collected there, Lithologically, Zos is hard to classify, how- including an exquisitely preserved skull with ever, it appears to be more ¯uvial than Ukhaa mandibles of Gobiderma pulchrum described Tolgod. At Zos the rocks are predominately in this paper. The lithology at Udan Sayr is red sandstone. Protoceratopsian specimens bright red to orange and similar to some of were collected, but have not been de®nitively the rocks at the Flaming Cliffs. No detailed identi®ed. New and unusual mammal and geologic investigations have occurred at this crocodile specimens were also collected. In- locality. terestingly, there is a Nemegt-type facies (containing a Nemegt-type fauna) that inter- tongues with the Djadokhta-like rocks at Zos. Ukhaa Tolgod Stratigraphically, this locality lies below During early July of 1993, the ®eld party Ukhaa Tolgod. Several lizard specimens of the Mongolian Academy of Sciences± were collected from the Zos locality. These American Museum of Natural History ex- include the holotype of a new iguanian (see pedition discovered Ukhaa TolgodÐone of description below). the most proli®c Djadokhta-like localities yet discovered (Dashzeveg et al., 1995; Nova- BARUN GOYOT LOCALITIES cek, 1996; Norell, 1997b). Ukhaa Tolgod is Khulsan exposed as a series of small cliffs, hills, and Khulsan is a large locality in the Nemegt bluffs (®g. 2). In this area spectacular fossils Basin (®g. 1). It is the type locality of the 10 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249

Barun Goyot Formation (Gradzinski and Jer- More than 20 lizard taxa have been de- zykiewicz, 1974a). Gradzinski and Jerzyk- scribed based on the specimens from this lo- iewicz (1974a, 1974b) considered the sedi- cality. These include six iguanians, 14 scin- ments of the Barun Goyot at Khulsan to be comorphs, and four anguimorphs (Sulimski, primarily eolian, however, due to an absence 1972, 1975, 1984; Borsuk-Bialynicka, 1984, of caliches and a greater proportion of clay 1985, 1988; Alifanov, 1988, 1993a, 1993b, and siltstones, they concluded that Barun 1996; Norell and Gao, 1997). Several lizards Goyot conditions were less arid than Dja- from this locality are also known from Dja- dokhta ones. This is further supported by the dokhta beds (e.g., Adamisaurus, Globaura, presence of obviously ¯uvial components Slavoia); whereas several other taxa com- (such as conglomerates) in a greater frequen- monly seen in the Djadokhta localities (e.g., cy in Barun Goyot rocks than in Djadokhta Isodontosaurus, Mimeosaurus) are unknown ones (Gradzinski et al., 1977). Compared to from this locality. the Djadokhta Formation, relatively little Lithologically, the above-mentioned local- published work has appeared on the Barun ities are predominantly formed of well sorted Goyot Formation, or the Khulsan locality, and cross bedded red sandstones, suggesting aside from several papers describing the fau- the presence of large dune ®elds in the Late na (e.g., Sulimski, 1975). Cretaceous. Some ¯uvial sediments are also The fauna at Khulsan appears to be dif- present, indicative of at least ephemeral wa- ferent from classic Djadokhta localities. Sev- ter in the interdunal environments. Although eral mammals appear to be distinct (Kielan- a variety of mechanisms have been proposed Jaworowska, 1974). The same is true for the regarding the origin of these deposits, current dinosaurs as no species level taxa (beyond consensus is that some, if not most, represent the possible occurrence of Velociraptor mon- predominantly eolian deposits (Jerzykiewicz goliensis) are reported from Khulsan and any et al., 1993; Eberth, 1993; Fastovsky et al., Djadokhta site. However, detailed study of 1997), with Ukhaa Tolgod being a notable the mammals (Novacek et al., in prep) and exception (Loope et al., 1998). These inter- the lizards (see later discussion) seems to pretations are, however, under review (Din- suggest that some of these perceived differ- gus and Loope, personal commun.). ences have been overstated. Lizard fossils The lithology of sediments at Ukhaa Tol- from this locality are referred to 17 species. god and other Djadokhta and Djadokhta-like Descriptions of these lizard taxa are covered formations, which often contain ``mature ca- in papers by several authors (Sulimski, 1975; liche paleosols'' (Jerzykiewicz, 1995: 244), Borsuk-Bialynicka, 1984; Norell et al., 1992; suggests that this region was an arid desert Alifanov, 1993b; this paper). when these rocks were deposited. Neverthe- less, intermittent water was present, both as Khermeen Tsav ponds and as small seasonal streams (Jerzyk- iewicz, 1995; Jerzykiewicz et al., 1993). At Khermeen Tsav is a large locality, where some localities extensive bioturbation and two separate rock units occur. The strati- root casts point to the presence of some plant graphically higher white beds are equivalent cover. of the loosely de®ned that Variation among these localities has two produce a fauna with tarbosaurs, big hadro- components: temporal and geographic. Mod- saurs, and ornithomimids. Beneath these are els have been proposed for each. Geograph- characteristic red rocks (the Red Beds of ically, Eberth (1993) proposed that the Dja- Khermeen Tsav of Gradzinski et al., 1977) dokhta-like beds were part of a large, Late that contain a rich Djadokhta-like fauna of Cretaceous basin where depositional condi- protoceratopsians (Bagaceratops rozhdest- tions were fairly uniform throughout, similar venskyi), velociraptorine dromaeosaurs, ovi- to many modern Central Asian basins like raptorids, and the ankylosaur Saichania chul- the Tarim. In a temporal context, assuming sanensis. Several extremely well-preserved sequential superposition of Djadokhta, Barun , including embryos, were recovered Goyot, and Nemegt rocks, Jerzykiewicz et al. from this locality (Elzanowski, 1977, 1981). (1993: ®g. 14) proposed that the arid Dja- 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 11 dokhta environment was sequentially re- dating have been identi®ed in these sedi- placed by less arid Barun Goyot conditions ments and there is a lack of reliable paleo- and ®nally mesic Nemegt ones. magnetic data (a situation that is being rem- How these formations, or how individual edied; L. Dingus, personal commun., 1998), localities, interrelate temporally is dif®cult to the absolute age of these localities is impos- address. On the basis of ``comparative stud- sible to determine at this time. Nevertheless, ies of dinosaurs and mammals,'' Gradzinski several ages have been proposed. All of these et al. (1977) suggested that the Barun Goyot are based on little or no direct evidence be- was temporally younger than the Djadokhta. yond faunal similarity at very high levels. Although many authors used supposed fau- For instance, Gradzinski et al. (1977) sug- nal differences among these localities to or- gested that the age of Djadokhta is ?late San- der them in time (for a consideration of the tonian/early Campanian and Barun Goyot lizards see later discussion in this paper), ?middle Campanian; whereas other authors subsequent intensive collecting at many these (Fox, 1978; Lillegraven and McKenna, 1986; localities caused many of these faunal differ- Jerzykiewicz and Russell, 1991) suggested ences to evaporate (Dashzeveg et al., 1995; that the Djadokhta and Barun Goyot forma- Gao and Norell, 1996; Dong, 1993; Jerzyk- tions are approximately equivalent in age, re- iewicz et al., 1993). Furthermore, since the spectively, to the middle and late Campanian Djadokhta and the Barun Goyot do not lie in (or the North American Judithian). Recently, superposition, it is impossible to determine new biostratigraphic evidence for the age of their direct stratigraphic relationships. Con- Djadokhta-like sediments in Mongolia and sequently there is little evidence to separate northern China was presented (Averianov, these localities temporally. Intraformational- 1997). This age estimate is based on the ly, some relationships are present. For in- common occurrence of isolated teeth of a stance, in the area around Bayn Dzak it is number of mammals in the Darbasa Forma- possible to determine that the Tugrugeen Shi- tion of southern Kazakhstan and at Mongo- reh locality lies above the red rocks of Bayn lian localities. These mammals seem to ex- Dzak, and Chimney Buttes (L. Dingus, per- hibit Djadokhta similarities (although it sonal commun., 1998). Furthermore, the re- should be stressed that they are quite frag- lationships of the sublocalities at Ukhaa Tol- mentary). In Kazakhstan, the Darbasa For- god have been determined (Dingus et al., in mation yields both terrestrial and marine fau- prep.). nas, the latter exhibiting an early Campanian Because no rocks suitable for radiometric fauna (Averianov and Nessov, 1995).

SYSTEMATIC PALEONTOLOGY SQUAMATA OPPEL, 1811 there is evidence to support the splitting of the Iguania into two major subgroups: the IGUANIA COPE, 1864 nonacrodontan iguanians and the acrodon- DEFINITION: The most recent common an- tans (Macey et al., 1997). cestor of Iguanidae*, * and Cha- maeleonidae, and all of its descendants (Es- IGUANIDAE (SENSU LATO: tes et al., 1988). NONACRODONTAN IGUANIANS) REMARKS: The monophyly of the Iguania Ctenomastax parva, new genus and species is well supported by a number of character Figures 3±4 states (Estes et al., 1988). The Iguania in- clude extant familial groups such as the Ig- ETYMOLOGY: ktenos ϩ mastax (Gr., f.), uanidae*, Agamidae*, and the Chamaeleon- comb-; referring to the comblike arrange- idae, and fossil groups such as the Arreto- ment of the marginal teeth of this lizard; par- sauridae Gilmore, 1943. The monophyly of vus (L.), meaning ``little.'' the Iguanidae* and the Agamidae* is still HOLOTYPE: IGM 3/61 (MAE 89/93-70), in- questionable (Frost and Etheridge, 1989), but complete skull with partial right and clear 12 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249

Fig. 3. Ctenomastax parva, new genus and species: A, B, IGM 3/61 (holotype), incomplete skull with mandibles from Zos, ventral and dorsal views. impression of the left ; preserved in only the posterior two thirds of Meckelian red ®ne-grained sandstones. canal. TYPE LOCALITY AND HORIZON: Zos, Ne- REFERRED SPECIMEN: IGM 3/62 (MAE megt Basin, Mongolian Gobi Desert; Upper 131), incomplete skull with mandibles, ®rst Cretaceous Djadokhta Formation. nine vertebrae and an incomplete scapula; KNOWN DISTRIBUTION: Zos and Khulsan from Khulsan (preserved in gray ®ne-grained localities, Djadokhta and Barun Goyot for- sandstones); Upper Cretaceous Barun Goyot mations. Formation. DIAGNOSIS: Distinguished from other non- acrodontan iguanians (or iguanids) in having DESCRIPTION the following derived character states: slen- der, ®ne teeth arranged in a ``comb-like'' The new is known from two speci- con®guration along the tooth row; tooth mens. The diagnostic features of the teeth crowns short and peglike; maxillary tooth and jaw structures are best shown on the ho- row slightly heterodont with anterior and lotype (®g. 3), whereas the and the posterior teeth larger than those in the middle palatal region are well preserved on the re- part of the tooth row; anterior one third of ferred specimen. The following description is Meckelian canal enclosed without fusion of based on both specimens. the dentary tube; retracted splenial covering SKULL ROOF: Skull is delicately built with 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 13

Fig. 3. Continued. a pointed snout. The premaxillae are fused as which medially articulates with the frontal a single element and exhibit a prominent dor- and posteriorly extends to the midlevel of the sal spine separating the nares. Six small uni- orbit. The anteroventral (orbital) process cuspid premaxillary teeth are present. The forms the anterior wall of the orbit, but ven- nasals are paired and extend posteriorly to trally does not contact the palatine. This pro- the level of the posterior borders of the pre- cess medially borders the orbitonasal fenestra frontal bosses. As in other iguanians, the (term sensu Oelrich, 1956). The prefrontal frontals are fused as a single bone and are contacts the lacrimal. Along this suture lies constricted between the orbits. Ventrally, a small notch (the lacrimal foramen). shallow subolfactory ¯anges form a trough The postorbital and postfrontal are un- for the olfactory tract. The dorsal surface of fused, separate elements. The left postfrontal the frontal is smooth anteriorly, but posteri- on the holotype is slightly shifted medially orly is lightly ornamented with rugosities an- beneath the frontal and parietal, but it shows terior to the parietal foramen. The frontopa- a forked condition with a slender anterior rietal suture is transverse, with a small pari- process and a short posterior process clasp- etal foramen opening at the suture (best ing the frontoparietal suture. The postorbital shown on IGM 3/62; see ®g. 4). slightly broadens posteriorly on the skull ta- The prefrontal is overlapped anteriorly by ble where it intrudes into the supratemporal the dorsal process of the maxilla. The pre- fenestra. frontal is exposed primarily on the dorsal ta- The parietal table is short and roughly ble of the skull and carries a prefrontal boss. trapezoidal. Laterally the parietal table is It also has a well-developed frontal process, strongly concave with a medial constriction. 14 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249

Fig. 4. Ctenomastax parva, new genus and species: A±C, IGM 3/62 (referred specimen), incomplete skull with mandibles from Khulsan, lateral, dorsal, and ventral views.

Ventrolaterally it has a steep ¯ange for the it becomes laterally compressed, forming a attachment of the temporal muscle, which crest as it turns posterolaterally to contact the extends continuously to the lateral surface of quadrate. The supratemporal is preserved on the supratemporal process of the parietal. both sides. It attaches to the lateral surface The dorsal surface of the parietal table is or- of the supratemporal process of the parietal, namented with small bumps with rugosities. and extends anteriorly to the midlevel of the This sculpturing is more developed than that supratemporal process. on the frontals. The posterior border of the In lateral view, the maxilla has a relatively parietal table is not a simple transverse mar- high dorsal process, which forms part of the gin. Rather, this margin consists of two lat- posterior border of the narial opening. The eral notches separated by a ¯at, posterior ex- premaxillary process of the maxilla is short, tension of the parietal table dorsal to the fo- overlapping the lateral extension of the pre- ramen magnum (®g. 4B). The supratemporal maxilla. An even stronger anteromedial pro- process of the parietal is longer than the pa- cess extends and meets its counterpart behind rietal table. In dorsal view, the supratemporal the premaxilla (on both the holotype and the process is triangular in cross-section adjacent referred specimen). Such a contact was pre- to the main body of the parietal. Posteriorly viously interpreted as an acrodontan syna- 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 15 pomorphy (Estes et al., 1988), but its occur- imen. However, preparation of the palatal re- rence in this and other nonacrodontan igu- gion of the referred specimen (IGM 3/62) anians (see below) from the Gobi indicates shows that the preserved left vomer has a that the character merits reevaluation. The clear midline edge separating it from the maxilla carries 19 highly pleurodont teeth right vomer (not preserved). In iguanians, (see below) on the holotype and 18 on the vomer fusion occurs only in chamaeleonids referred specimen. Dorsal to the maxilla, the (Rieppel, 1981), and the paired condition is ventral rim of the orbit is formed by the an- a primitive character state for squamates gen- terovental process of the jugal and a small erally (Estes et al., 1988). The suture be- lacrimal. As in other iguanians, the postero- tween the vomer and the palatine cannot be dorsal process of the jugal extends to meet clearly delimited, but the palatine is slightly the squamosal ventral to the postorbital. The widened and has a small lateral process that squamosal is missing on the holotype, but is overlaps the palatal process of the maxilla. preserved on both sides of the referred spec- The lateral edge of the palatine forms the en- imen. It has a slightly widened base that ar- tire medial border of the suborbital fenestra, ticulates with the quadrate, and a slender an- which is narrow and slightly elongated. The terior process contacting the postorbital and medial edge is slightly damaged, but shows abutting the jugal. no indication of a midline contact with its The quadrate is straight and lightly built. counterpart to close the interpterygoid va- Its dorsal end expands posteriorly slightly. It cuity. Posteriorly, the palatine has an irreg- has a well-developed cephalic condyle that is ular diagonal sutural contact with the ptery- covered by the squamosal in the holotype. goid. Posterolaterally, the suture originates at The anterior surface of the quadrate is a ver- the posterior border of the suborbital fenes- tical plate with a smooth surface penetrated tra, but extends anteromedially, ending at the by a small quadrate foramen dorsal to the midlevel of the interpterygoid vacuity. The ventral condyle. This foramen forms the pas- pterygoid has a short and wide anterior (or sageway for an anastomotic branch of the an- palatal) process, which is about half the terior tympanic vein and a small anastomotic length of the posterior (or quadrate) process. branch of the posterior condylar artery (Oel- Due to its oblique sutures with the palatine, rich, 1956). The lateral (tympanic) crest is the anterior process of the pterygoid is vertical and curves slightly posteriorly form- roughly triangular. The lateral process of the ing the margin of the tympanic membrane. pterygoid is even shorter and forms the The medial border of the anterior surface of weakly developed pterygoid ¯ange. Dorso- the quadrate is marked by the medial crest medial to the lateral process, the epiptery- which ventrally has a small notch for inser- goid sets in a small columellar fossa at the tion of the quadrate process of the pterygoid. base of the quadrate process. All the palatal The ventral condyle is much smaller than the elements are toothless. cephalic condyle and sets in the articular fos- BRAINCASE: The ¯oor of the braincase is sa of the lower jaw, which has an anterior well preserved on both specimens, but the buttress enhancing the jaw joint (®g. 4A). dorsal part of the lateral wall of the braincase The posterior crest is much more robust than is not preserved. Only the ventral half of the the tympanic crest. It originates on the ce- right epipterygoid is preserved as a vertical phalic condyle as a prominent ridge that pillar. The basipterygoid process of the ba- curves ventrally and disappears dorsal to the sisphenoid is short and slender and articu- ventral condyle. Lateral to this crest is a dor- lates with the grooved medial surface of the sally expanded triangular fossa. The postero- pterygoid. The ventral surface of the basi- medial surface of the quadrate is also trian- sphenoid is slightly depressed, as seen in gular. The thin medial crest is oblique in pos- many other iguanians. Posteriorly, the basi- terior view. The posterior opening of the sphenoid is sutured to the basioccipital. This quadrate foramen is dorsal to the quadrate- suture is slightly arched anteriorly (®g. 3A, pterygoid articulation. 4C). The basioccipital posterolaterally forms PALATAL ELEMENTS: Much of the palatal the small spheno-occipital tubercle, which is region can not be examined on the type spec- ventrally directed. Laterally it displays a 16 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249 roughly triangular occipital recess. Antero- Posterodorsal to the splenial, the medial lateral to the occipital recess, the recessus exposure of the coronoid is triradiate, lacking vena jugularis (or vena capitis lateralis of the posterodorsal process seen in some extant others) is poorly preserved. It is a relatively iguanians (see Frost and Etheridge, 1989: ®g. shallow trough where the posterior opening 4). Ventral to the coronoid, the anterior part to the Vidian canal is located anteriorly dor- of the angular is exposed as a tonguelike ex- sal to the base of the basipterygoid process tension, which turns from lateral to the me- and within the basisphenoid. The foramen dial side of the jaw, separating the splenial ovale lies anterior to the occipital recess. The and the dentary to the level of the anterior facial foramen is not preserved on either side inferior alveolar foramen. Immediately be- of the type. hind the posteroventral process of the coro- Although the occiput is badly damaged, noid, the mandibular fossa opens as a narrow some elements are still identi®able on IGM and shallow groove extending posteriorly to- 3/62. The supraoccipital is not preserved. wards the craniomandibular joint. As shown The right paroccipital process is missing, and on both the holotype and the referred speci- the left is displaced below the supratemporal men, the angular process is strongly devel- arch and in front of the quadrate. The occip- oped, directed medially and not hooked at ital condyle is formed predominately by the all. basioccipital, with little contribution from the In lateral view, the dentary occupies the exoccipitals. Dorsolateral to the occipital anterior half of the mandible and posteriorly condyle, the exoccipital is partially preserved terminates at the level of the anterior sur- on both sides. It forms the posterior rim of angular foramen. This proportion is a de- the occipital recess, and contributes in small rived condition among iguanians, as Sphen- part to the spheno-occipital tubercle and the odon and some extant iguanians have a lateral part of the occipital condyle. The bet- greater proportion of the dentary in relation ter preserved right side seems to show that to the postdentary part of the jaw. Neither the exoccipital is broken at the hypoglossal of the two specimens has the lateral coro- foramina. noid process preserved. But the referred MANDIBLE: Both mandibles are well pre- specimen displays a clear articular surface served on the referred specimen, but the di- anterior to the anterior surangular foramen, agnostic medial side of the dentary and teeth indicating that the lateral coronoid process are best exposed on the holotype, in which a has a triangular anterior border and covers matrix impression shows the sutures and en- the dorsal part of the dentary-surangular su- closure of the Meckelian canal. Both the ho- ture (®g. 4A). A small coronoid process of lotype and the referred specimen show that the dentary slightly covers the anterior sur- the canal is closed anteriorly for about one face of the dorsal process of the coronoid third of its length; the presence of a clear bone. The posterior extent of the dentary is suture indicates that the dentary tube is en- not preserved on either specimen, but based closed but not fused. The posterior two thirds on observation of the referred specimen, it of the canal is medially covered by a narrow seems to terminate below the anterior sur- splenial. The anterior inferior alveolar fora- angular foramen. The latter specimen seems men and the anterior mylohyoid foramen are to have a small notch on the dentary for ar- located in close approximation. The former ticulation with the surangular and angular foramen is larger than the latter and is locat- bones. ed at the anterior end of the splenial, whereas The posterior surangular foramen, much the anterior mylohyoid foramen lies at the smaller than the anterior one, is located pos- ventral border of the splenial. Location of the teriorly near the dorsal border of the jaw and posterior mylohyoid foramen (ϭ angular fo- anterior to the craniomandibular joint. As in ramen of other authors) cannot be deter- many other iguanian lizards, the articular and mined on either of the specimens, as a matter prearticular are fused. The retroarticular pro- of preservation. The splenial terminates pos- cess is slightly stronger than the angular pro- teriorly at the level of the coronoid summit cess and is directed posteriorly, in contrast to of the jaw. the de¯ected condition in several lizard 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 17 groups including gekkotans, scincoids, and three taxa are small and nearly equivalent in varanids (see Estes et al., 1988). The process size, indicating that differences in the shape has a depression on its dorsal surface, which of the parietal table are not due to ontoge- provides the insertion for the dorsal ®bers of netic or allometric factors. Furthermore, the pterygomandibularis muscle (Oelrich, has tricuspid teeth that are very different 1956). from the peglike dentition of Ctenomastax DENTITION: The marginal teeth are gener- parva. Polrussia has unicuspid teeth, that ally peglike in lateral view, but are highly ``protrude high above the parapet of the jaw'' pleurodont, having over two thirds of the (Borsuk-Bialynicka and Alifanov, 1991). tooth height attached to the lateral parapet of Ctenomastax parva with its low crowned the . As the teeth have very slender teeth clearly differs from Polrussia. Further- shafts and are closely spaced, they show a more, the new taxon lacks the fusion of the comblike arrangement along the tooth row. dentary tube seen in Polrussia. The crowns are unicuspid, having no cusp- A notable character in Ctenomastax parva ules but displaying weak lateral crests. is the contact of the maxillae behind the pre- The marginal teeth of Ctenomastax parva maxillary spine. This character was regarded are weakly heterodont: the ®rst two or three as an acrodontan synapomorphy by Estes et teeth on the maxillary and dentary tooth al. (1988) based on its distribution in extant rows are enlarged and are more or less ca- iguanians (but see Jollie, 1960). However, niniform, the middle teeth are much smaller the dentition of the new species is highly than the anterior ones, and a few posterior pleurodont, the postfrontal remains as a sep- teeth are larger than those in the middle part arate element from the postorbital, and the of the tooth row. However, there is no dif- Meckelian canal is closed anteriorly. These ferentiation of crown pattern along the tooth characters strongly indicate that the new spe- row. The complete maxillary tooth row in- cies represents a nonacrodontan iguanian (or cludes 19 positions on the holotype and 18 iguanid), and cannot be classi®ed in the Ac- on the referred specimen. The complete den- rodonta. Furthermore, this same character oc- tary tooth row is best shown on the holotype, curs in several other nonacrodontan iguani- in which a total of 23 teeth are preserved as ans from the Gobi, and suggests such a con- clear impressions. As mentioned before, the tact could well be a primitive character state premaxilla is a single element that bears six small unicuspid teeth. among iguanians. The relationships of the new species with other nonacrodontan iguanians is currently COMPARISON AND DISCUSSION unclear. Like some other nonacrodontan ig- The new taxon Ctenomastax parva shares uanians described from the Gobi Desert, the following characters with other iguani- Ctenomastax parva shares a large number of ans: frontals are fused and constricted be- characters with crotaphytine iguanians: (1) tween the orbits; presence of a frontal shelf lacrimal foramen not enlarged; (2) skull roof that anteriorly underlies the nasals; parietal not strongly rugose; (3) jugal and squamosal foramen located anteriorly on the frontopa- not broadly juxtaposed; (4) parietal table rietal suture; and presence of an angular pro- trapezoidal; (5) parietal foramen in fronto- cess on the retroarticular process of the lower parietal suture; (6) supratemporal on lateral jaw. Other characters listed in Estes et al. side of supratemporal process of parietal; (1988) as iguanian synapomorphies are not (7) dentary not expanded onto labial face of preserved on the specimen. coronoid; (8) labial blade of coronoid ab- Two nonacrodontan iguanians described sent; (9) anterior surangular foramen above by Borsuk-Bialynicka and Alifanov (1991) posteriormost extent of dentary; (10) den- from Khulsan (Igua and Polrussia) have tary tube not fused; (11) splenial relatively short, wide, and rectangular parietal tables. long anteriorly; (12) marginal teeth pleuro- By contrast, Ctenomastax parva, known dont. Many of these characters are plesiom- from the same locality, has a trapezoidal pa- orphic for the Iguania, providing little in- rietal table. All of the specimens of these formation regarding the relationships of the 18 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249 new lizard except for possibly indicating its specimens preserve complete nasals, but im- primitive status. pressions on the holotype and IGM 3/70 in- dicate that the nasals are paired and laterally Temujinia ellisoni, new genus and species in contact with the maxillae. The frontals are Figures 5±6 fused and have an interorbital constriction. The holotype shows a frontal shelf is present ETYMOLOGY: Temujin, Mongolian name of anteriorly to underlay the nasal and an an- the world conqueror Genghis Khan; species terolateral spike is developed between the epithet after Mick Ellison, Principal Artist at nasal and prefrontal. The dorsal surface of the American Museum of Natural History, the frontals is lightly ornamented with ru- who skillfully prepared the photographs and gosities. The frontoparietal suture is trans- outline drawings for this work. verse, with the parietal foramen slightly chip- HOLOTYPE: IGM 3/63 (MAE 121/93-93), ping the anterior margin of the parietal, but incomplete skull with mandibles. largely opening on the frontal side of the su- TYPE LOCALITY AND HORIZON: Ukhaa Tol- ture (see ®g. 5A). god, Nemegt Basin, Mongolian Gobi Desert; The parietal table is roughly trapezoidal, Upper Cretaceous Djadokhta Formation and the dorsal surface is weakly ornamented (Loope et al., 1998). anteriorly with rugosities, as on the frontals. KNOWN DISTRIBUTION: Ukhaa Tolgod and The maximum width of the parietal table is Tugrugeen Shireh localities, Djadokhta For- anteriorly at the frontoparietal suture and the mation. minimum width at the posterior margin DIAGNOSIS: Differing from other iguanians (slightly wider than half the width at the in having the following derived character frontoparietal suture); therefore, the parietal states: postfrontal forms slender bar between table has no obvious constriction at the mid- orbit and supratemporal fenestra; parietal fo- dle level. However, the parietal laterally de- ramen opens largely on frontal side of fron- velops a relatively deep ¯ange, indicating a toparietal suture; posterior margin of parietal dorsal origin of the temporal muscle. As a symmetrically notched for insertion of dorsal distinct character of the species, the posterior axial muscle; presence of vertical ridges and margin of the table is symmetrically notched grooves on dorsal process of coronoid for in- for the insertion of dorsal axial musculature sertion of mandibular adductor muscle; an- (spinalis capitis). The supratemporal process terior surangular foramen opens dorsally be- of the parietal is slightly longer than the table hind dorsal process of coronoid; anterior half and extends posterolaterally at a roughly 45Њ of Meckelian canal closed by dentary with- angle in relation to the midline of the skull. out fusion; mandibular fossa narrow and The process is strongly compressed laterally, elongate; marginal teeth low crowned and having a dorsal crest and a deeply sloped lat- strongly swollen; tooth crowns weakly tri- eral surface for attachment of temporal mus- cuspid; angular process of mandible wide cles. and strong, directed medially. The prefrontal has an elongate frontal pro- REFERRED SPECIMENS: IGM 3/64±3/69 cess, which extends posteriorly along the lat- (MAE 145/94-40, 75/93-89, 235/93-130, eral edge of the frontal to the midpoint of the 319/93-147, 39/93-90, MAE 94-37), all to- dorsal border of the orbit. The new species potypic incomplete skulls with mandibles shares this character with Ctenomastax (see (see discussion below); IGM 3/70 (MAE 19/ above) and extant (see Blanc, 1977: 93-6), fragmentary skull with mandibles ®g. 26), but the phylogenetic signi®cance of from Tugrugeen Shireh (Tugrikin-Shireh). this character state needs to be evaluated on the basis of a broader survey. Anterolaterally, DESCRIPTION the prefrontal forms a very weak prefrontal SKULL ROOF: The premaxillae are not pre- boss. The anteroventral (orbital) process is served on the holotype, but are present on slightly concave anteriorly, forming the an- several referred specimens (IGM 3/64, 3/66, terior wall of the orbit and ventrally contacts 3/68). The premaxillae are fused into a single the widened palatine. This process medially element with a slender spine. None of the borders the orbitonasal fenestra and laterally 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 19

Fig. 5. Temujinia ellisoni, new genus and species: A±C, IGM 3/63 (holotype), incomplete skull with mandibles from Ukhaa Tolgod, dorsal, ventral, and lateral views. 20 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249

Fig. 6. Temujinia ellisoni, new genus and species (referred specimens, topotypic): A, IGM 3/69, incomplete skull with mandibles, right lateral view; B, IGM 3/64, incomplete skull with mandibles, dorsal view; C, IGM 3/65, incomplete skull with mandibles, dorsal view. contacts the lacrimal bone. The lacrimal fo- medial edge of the prefrontal is separated ramen is small, differing from the enlarged from the nasal by a slender anterolateral pro- condition seen in acrodontans. The relation- cess of the frontal (®gs. 5A, 6B). ship of the prefrontal with the nasal is un- The postfrontal and postorbital are clearly clear, but at least the large part of the antero- delimited by a V-shaped suture, and a small 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 21 wedge of the postorbital ®ts in the lateral extends ®rst posterodorsally then nearly hor- edge of the postfrontal. The postfrontal is re- izontally to contact the postorbital and the duced, but is present as a slender bar sepa- squamosal. The anterovental process is rating the orbit from the supratemporal fe- mounted on the dorsal edge of the maxilla nestra (not con®ned to the orbital rim); it is and forms most of the ventral rim of the or- medially forked to clasp the frontoparietal bit. Anterior to the jugal is a small lacrimal, suture. Such a postfrontal differs from that in which forms the anteroventral corner of the extant iguanians, which is con®ned to the orbit. posterodorsal margin of the orbit (see de PALATAL ELEMENTS: The vomers are not Queiroz, 1987; Estes et al., 1988). The pos- preserved on the holotype, but the articular terior process is short and robust, ®tting in a surface on the palatine indicates the vomers small notch on the parietal, but the anterior are paired as in other iguanians except for process is long and slender, almost twice the chamaeleonids. The palatine has a vomerine length of the posterior process. The body of process. Posteriorly the palatine is wide, the postfrontal is thickened and is more rod- forming most of the ¯oor of the orbit. An- like than platelike, differing from other igu- teromedially within the orbit, a small process anian species. The postorbital is subtriangu- meets its counterpart, forming the ventral lar with a large, wide anterior process and a border of the orbitonasal fenestra. Posteriorly pointed posterior process that contacts the it lacks sutural contact along the midline, squamosal. The lateral edge of this element leaving a narrow opening of the interptery- is slightly grooved for the posterodorsal pro- goid vacuity (pyriform recess of Oelrich, cess of the jugal, which contacts the anter- 1956; Estes et al., 1988). Anterolaterally oventral side of the squamosal (the posterior within the orbit, a small lateral process of the tip of the jugal process is preserved with the palatine overlaps the palatal ¯ange of the squamosal). maxilla, and it is through this process that The squamosal is missing on the right side the infraorbital canal penetrates the palatine. but completely preserved on the left. This el- The palatine contributes the anterior two ement is also transversely expanded like the thirds of the medial border of the suborbital postorbital. It has no dorsal process, but its fenestra, with the posterior one third formed posterior end is hooked laterally in dorsal by the pterygoid. As in many other lizards, view. The supratemporal is not preserved on the ectopterygoid forms both part of the pos- the holotype, but other specimens (e.g., IGM terior as well as the lateral border of the fe- 3/66, 3/68) show a small splint, which lies nestra, and its anterolateral process does not between the squamosal and the supratempor- extend to meet the palatine. al process of the parietal as in many other The anterior (palatine) process of the pter- lizards. ygoid has a wide base and contacts the pal- The maxilla, jugal, and lacrimal are pre- atine along a transverse suture when viewed served on the right side of the holotype. dorsally. Ventrally, however, the suture is These elements are also preserved on several oblique with a short anterior extension of the referred specimens. The maxilla is relatively pterygoid along the ventromedial edge of the low and carries a dorsal process, the summit palatine (®g. 5B). The short lateral process is of which is slightly anterior to the midpoint articulated with the ectopterygoid, and ven- of the tooth row. As in Ctenomastax parva, trally forms a weak pterygoid ¯ange. Dor- an anteromedial process of the maxilla con- sally near the base of the posterior (quadrate) tacts the opposite element behind the dorsal process, a small socket (the fossa columella) spine of the premaxillae (best shown in IGM is developed for the epipterygoid articula- 3/64, 3/68). The maxilla bears teeth and tooth tion. However, the epipterygoid on the ho- spaces for 21±22 positions (see description lotype is displaced on both sides, so the ven- of dentition below). The posterodorsal pro- tral end of the left epipterygoid abuts the cess of the jugal on the holotype is broken basipterygoid process, and the right epipter- above the coronoid process and at the middle ygoid lies horizontally across the ventral sur- part of the postorbital rim. However, IGM 3/ face of the basioccipital (®g. 5B). A deep 64 preserves a complete bar (see ®g. 6B) that notch, forming the synovial joint, lies slight- 22 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249 ly anteroventral to the basipterygoid process. cess by a prominent ridge (crista interfenes- As in many other lizards, the notch has an tralis of SaÈve-soÈderbergh, 1947; Oelrich, anterior buttress, preventing the process from 1956). Within the occipital recess, two open- sliding forward. Posterior to the joint, the lat- ings are clearly identi®able: dorsal to the re- erally smooth and convex quadrate process cess is a smaller foramen perilymphaticus, is medially grooved, possibly allowing a slid- and deep in the recess is the larger foramen ing motion of the basipterygoid process. The rotundum. posterior end of the process becomes later- The lateral wall of the braincase lacks a ally compressed and extends to support the clearly de®ned alar process of the prootic quadrate. (best shown on IGM 3/68, 3/70), and thus BRAINCASE: The braincase ¯oor is well the dorsal part of the epipterygoid lays preserved on the holotype and several of the against the otic capsule directly (IGM 3/68). referred specimens (e.g., IGM 3/68). On the The alar process provides an origin of the holotype, the basisphenoid is complete ex- pseudotemporalis profundus (see Oelrich, cept for the parasphenoid process, which is 1956). Lack of an alar process indicates fun- missing, possibly because it was cartilagi- damental differences in the development, or nous in life. The basipterygoid process has a the origin, of these muscles compared to oth- slender shaft but a strongly expanded con- er iguanians that have this process. Ventral dyle for articulation with the pterygoid. The to the anterior semicircular canal, a weak tri- main part of the basisphenoid has a small geminal notch is developed as the passage- depression on its ventral surface, and carries way for the trigeminal nerve (V). Antero- a short posterolateral process extending to ventral to the notch, the inferior process of the base of the spheno-occipital tubercle. the prootic (best shown on IGM 3/70) is well Owing to the development of this lateral pro- developed and anteriorly sutures to the well- cess, the basisphenoid-basioccipital suture is ossi®ed pila antotica. The posterior process laterally oblique rather than transverse. The of the prootic is triangular, extending pos- basioccipital is roughly equivalent in size terolaterally along the anterior surface of the with the basisphenoid. Located laterally, at paroccipital process and terminating near the the midlevel of the basioccipital, the spheno- tip of the process. Dorsally at the base of the occipital tubercle is more ventrally than pos- posterior process, a minute foramen (?endo- teriorly directed. The occipital condyle is ro- lymphatic foramen) opens near the prootic- bust in relation to the size of the basioccip- supraoccipital suture on the prootic. ital. Corresponding lateral components of the In posterior view, the supraoccipital is exoccipital form two thirds of the occipital hexagonal, having a very low occipital crest condyle, while a medioventral one third is limited to the anterodorsal part of the bone. composed of basioccipital. Part of the anterior and most of the posterior Dorsolateral to the braincase ¯oor is a semicircular canals are covered by the supra- deep and wide trough, which is the recessus occipital. The posterior dorsal surface of the vena jugularis (term of Oelrich, 1956). The supraoccipital is a slightly convex and lateral wall of the trough is formed by a well- smooth slope, and its posterior edge is arched developed crista prootica of the prootic, but anteriorly as the dorsal rim of the foramen the medial wall is composed of both the pro- magnum. The supraoccipital is sutured lat- otic and a dorsal extension of the basisphe- erally with the prootic and posterolaterally noid (without contribution from the basioc- with the exoccipital. Lateral to the foramen cipital). Anteriorly within the recessus, the magnum, the exoccipital serves multiple posterior opening of the Vidian canal pene- functions as in many other lizards: it forms trates the basisphenoid and opens postero- a posterolateral wall of the braincase, the lat- dorsal to the base of the basipterygoid pro- eral border of the foramen magnum, the bas- cess. The facial foramen for the facial nerve al part of the paroccipital process (fused with (VII) opens on the arched roof of the reces- the opisthotic), the posterior rim of the oc- sus. More posteriorly, the foramen ovale cipital recess, and part of the occipital con- opens dorsolateral to the spheno-occipital tu- dyle. In posterior view, the exoccipital forms bercle, and is separated from the occipital re- a triangular surface, which medially sutures 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 23 with the spheno-occipital tubercle and later- nent dorsal process, which forms the anterior ally borders the occipital recess by its crista buttress for the craniomandibular joint. tuberalis (best shown on the holotype and The angular is a narrow tonguelike ele- IGM 3/68). Lateral to the occipital condyle, ment exposed ventral to the surangular. An- the triangular surface is penetrated by three teriorly it ®ts into the posterior notch of the foramina, which are arranged as a triangle: dentary below the surangular, and posteriorly dorsally lies the foramen for the vagus nerve it terminates well anterior to the angular pro- (X), and ventrally are two foramina for the cess and ventral to the posterior surangular hypoglossal nerve (XII). This condition is foramen. Sharply different from the condi- different from and Cten- tion in Anchaurosaurus gilmorei, the angular osaura pectinata, in which three rami of the in this species forms part of the ventral bor- hypoglossal nerve emerge through three sep- der of the postdentary part of the jaw, but is arate foramina in the exoccipital bone (Wil- not exposed on the medial side of the jaw. lard, 1915; Oelrich, 1956). In medial view, the anterior one third of MANDIBLE: The mandibles on the holotype the Meckelian canal on the holotype is closed are well preserved except for the anterior by a strong medial and upward enrolling of tips, which are missing due to breakage. In the ventral edge of the dentary; however, the lateral view, the dentary makes up roughly enclosure of the dentary tube is unfused. the anterior half of the mandible, having a Most of the referred specimens consistently strongly convex lateral surface. The left den- show the same morphology as the holotype, tary is better preserved than the right, and is but IGM 3/69 has the canal slightly open me- broken anteriorly at the fourth or the ®fth dially. The splenial is reduced, restricted to tooth position (determined by comparison the posterior two thirds of the Meckelian ca- with IGM 3/64). Posteriorly, the dentary is nal. Posteriorly, it terminates at the same lev- slightly notched for the short anterior exten- el as the posteroventral process of the den- tary. The anterior inferior alveolar foramen sion of the surangular and angular. The pos- and the anterior mylohyoid foramen pene- terior extremity of the dentary terminates at trate the splenial close to the midpoint of the the level below the summit of the coronoid. tooth row. The ventral border of the mandible is slightly The mandibular fossa is a very narrow and ¯attened, as the jaw is not strongly com- elongate slit, opening horizontally between pressed laterally, but is rather convex. the prearticular and the surangular; it has an The coronoid has no lateral blade. Instead anterior border immediately behind the pos- it displays a robust dorsal process with two teroventral process of the coronoid and pos- prominent vertical ridges on its lateral sur- teriorly extends to a point below a prominent face for attachment of the mandibular adduc- process of the surangular anterior to the cran- tor muscle. The surangular occupies the dor- iomandibular joint. At the posterior end of sal posterior half of the mandible and has an the mandible, the prearticular is entirely anterior process ®tting into the posterior fused with the articular and is partially fused notch of the dentary together with the ante- with the surangular; only a short suture pos- rior process of the angular. The lateral sur- terior to the angular can be delimited from face of the surangular has a strong horizontal the latter element. Medial to the cranioman- crest (adductor crest) for attachment of the dibular joint, the prearticular bears a wide jaw muscles. The anterior surangular fora- and strong angular process, which is perpen- men (®gs. 5C, 6A) is located dorsal to the dicular to the retroarticular process in direc- crest and right at the coronoid/surangular su- tion. The retroarticular process is best pre- ture posteroventral to the dorsal process of served on the holotype and IGM 3/69 (®gs. the coronoid. The posterior surangular fora- 5B, 6A). Both the specimens show that the men is much smaller than the anterior fora- process is posteriorly directed, having its lat- men (about half the size of the latter), and is eral border curved medially at the base. located below the adductor crest and anter- DENTITION: The premaxillary teeth are not oventral to the craniomandibular joint. Pos- preserved on the holotype, but other speci- terodorsally, the surangular bears a promi- mens (e.g., IGM 3/64, 3/68) show that the 24 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249 fused premaxilla carries ®ve to six unicuspid group (see Estes et al., 1988 for evaluation): teeth. The maxillary teeth are best preserved frontals are fused and constricted between on IGM 3/69, which shows a nearly com- orbits; frontal shelf anteriorly underlies the plete tooth row containing 20 positions. A nasals, with frontals exposed anterolaterally complete maxillary tooth count can be esti- as prominent spikes; prefrontal bosses are mated as 22 based on comparison of this present; postfrontal is reduced; parietal fo- specimen with IGM 3/64. The dentary teeth ramen is displaced anteriorly; and the pres- are best preserved on the holotype and IGM ence of an angular process of the mandible. 3/69, and a complete dentary tooth row as Possession of these iguanian synapomor- shown on the latter specimen contains a total phies, but lack of acrodontan autapomorphies of 25 positions. (see Estes et al., 1988) indicate the nonacro- The tooth attachment is pleurodont, having dontan position of the new taxon within the about two thirds of the columnar tooth shaft Iguania. attached to the relatively deep lateral parapet Compared with other nonacrodontan igu- of the jaws. The teeth in lateral view have anians from the Gobi, this taxon differs from short crowns. The ®rst two or three maxillary Anchaurosaurus (Gao and Hou, 1995, 1996) teeth are unicuspid, followed by several bi- in having the frontal process of the prefrontal cuspid teeth, then well-de®ned tricuspid teeth extended to the middle level of the orbit, in the middle and posterior part of the tooth much weaker frontal bosses, and short- row. The tricuspid crowns are laterally swol- crowned and swollen teeth. It differs from len, having a prominent central cusp and Igua and Polrussia in having a short, trape- smaller but symmetrical lateral cusps (see zoidal parietal table with longer supratem- ®gs. 5C, 6A). From anterior to posterior poral process, and differs from the above- along the tooth row, the teeth become in- described Ctenomastax primarily in having creasingly stouter and the tricuspid cusps be- short-crowned and tricuspid teeth. come more pronounced. Compared with extant nonacrodontan ig- uanians, it is worth noting that the new spe- COMPARISON AND DISCUSSION cies shares the following characters with the Madagascan Oplurus (see Blanc, 1977): the Recognition of the new taxon Temujinia frontal process of the prefrontal is strongly ellisoni is primarily based on the holotype. elongate; the parietal table is short and trap- Several specimens (e.g., IGM 3/68, 3/69, 3/ ezoidal, with a lateral ¯ange extending onto 70) can be con®dently referred to the same the lateral surface of the supratemporal pro- species, whereas the referral of several other cess; the palatal elements are expanded trans- specimens (IGM 3/65, 3/66, 3/67) to the spe- versally; the mandibular fossa opens as an cies is tentative. In comparison with the ho- elongate narrow slit. The phylogenetic sig- lotype, the latter three skulls are more slen- ni®cance of these shared characters merits derly built with a more pointed snout. How- further investigation. ever, these specimens possess most of the di- One interesting cranial feature displayed in agnostic features of the species (see above), Temujinia ellisoni is the forked postfrontal supporting referral to the same species as the (see also description of Ctenomastax parva). holotype. IGM 3/65 shows a frontal tab over- A forked postfrontal that clasps the fronto- lapping the parietal (indicating a less mov- parietal suture is absent in extant iguanids able frontoparietal hinge) and the parietal fo- and this character has been interpreted as a ramen opens within the frontal tab (see ®g. synapomorphy of (Estes et al., 6C). However, because this is the only spec- 1988; Scincogekkonomorpha of Sukhanov, imen showing this feature and the other two 1961). However, presence of such a forked specimens with similar skull con®gurations condition in the Late Cretaceous iguanids are poorly preserved, we cannot determine from the Gobi indicates that the status of this the signi®cance of this feature. character in squamate requires re- The new species Temujinia ellisoni is evaluation. As these may represent basal ig- clearly referable to the Iguania on the basis uanians, the forked condition may well be a of the following diagnostic characters of the primitive state for lizards generally, and the 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 25

nonforked condition in extant iguanians is DESCRIPTION probably a derived condition within the . SKULL ROOF: The holotype skull is undis- Another notable feature about this new torted and is preserved in a dark brown taxon is the maxillary contact behind the pre- coarse-grained sandstone concretion. The maxillary spine. Among the Late Cretaceous premaxillae are not preserved on the holo- iguanians from the Gobi, both Temujinia el- type or the referred specimen. The left nasal lisoni and Ctenomastax parva show such a is incompletely preserved, but is the only contact. As discussed above, occurrences of remnant of this element present. Its posterior such a contact in these Cretaceous nonacro- end is slightly displaced ventral to the fron- dontan iguanians raise the question about the tal; however, a depression clearly indicates apomorphic status of the character for acro- that the frontal has an anterior tab, which is dontans and indicate that the character merits overlapped by the nasal as in other iguanians. further evaluation. The fused frontals are more slender than in Anchaurosaurus gilmorei, and the frontopa- rietal suture is slightly posterior to the level Zapsosaurus sceliphros, of the coronoid process of the lower jaw. As new genus and species in Anchaurosaurus gilmorei, the parietal fo- Figure 7 ramen opens at the frontoparietal suture, but is signi®cantly enlarged on the parietal side. ETYMOLOGY: zaps ϩ sauros (Gr., m.), Only an anterior rim occurs on the frontal meaning storm lizard; skeliphros (Gr.), (®g. 7C). The parietal table is short and trap- meaning thin or slender, in reference to the ezoidal. It differs from Anchaurosaurus gil- lightly built skull of the new species. morei in having a strongly developed poste- HOLOTYPE: IGM 3/71 (MAE 255/92-10), rior shelf or ¯ange, which is divided by a incomplete skull articulated with mandibles. weak median ridge and is laterally extended TYPE LOCALITY AND HORIZON: Tugrugeen onto the base of the supratemporal process. Shireh, Mongolian Gobi Desert; Upper Cre- The process is slender and strongly elongate, taceous Djadokhta Formation (Jerzykiewicz bearing a sharp dorsal crest. Attached to the et al., 1993; Fastovsky et al., 1997). posterolateral surface of the supratemporal KNOWN DISTRIBUTION: Only known from process, the supratemporal bone is a much the type locality and horizon. stronger element than in Anchaurosaurus gil- DIAGNOSIS: Distinguished from possibly morei, and it has a ¯at dorsal surface. closely related Anchaurosaurus gilmorei by The prefrontal is preserved on both sides. having the following character states: pre- It has a weak prefrontal boss, contrary to the frontal bosses weakly developed; posterior strong lateral projection seen in Anchauro- border of parietal strongly ¯anged for attach- saurus gilmorei (see Gao and Hou, 1995: ®g. ment of axial musculature; Meckelian canal 1). Posteromedially, the prefrontal has a slen- closed below anterior three-fourths of tooth der frontal process whose posterior extent row; splenial strongly reduced, covering only lies at the midlevel of the orbit. The post- posterior one fourth of Meckelian canal; lat- frontal is probably separated from the post- eral surface of coronoid dorsal process bears orbital (indicated by the articular surface on vertical crest associated with a ventral tuber- the frontal), but the actual status of this ele- cle; presence of distinct medial ¯ange of sur- ment cannot be ascertained because of poor angular anteromedial to craniomandibular preservation. Extant nonacrodontan iguani- joint; mandibular fossa strongly shortened, ans normally retain a reduced postfrontal posteriorly terminating halfway between cor- (Estes et al., 1988). A comparison with An- onoid and craniomandibular joint; marginal chaurosaurus gilmorei is impossible, as this teeth having short shafts, but strongly ¯ared region of the skull is not preserved on any crowns. known specimens of the latter species. REFERRED SPECIMEN: IGM 3/72 (MAE 20/ The squamosal is incompletely preserved 93-15), left upper and lower jaws (topotyp- on the right side, and it has been slightly dis- ic). placed medially. The bone has a broad pos- 26 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249

Fig. 7. Zapsosaurus sceliphros, new genus and species: A±D, IGM 3/71 (holotype), incomplete skull with mandibles from Tugrugeen Shireh, lateral, dorsal, and ventral views. 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 27

Fig. 7. Continued. 28 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249 terior end, limiting the size of the supratem- clear impression allows the morphology of poral fenestra. Because the bone is poorly this element to be described. Its anteroventral preserved, the contact of this element with process is relatively deep, roughly rectangu- the postorbital and the jugal cannot be iden- lar, and forms the ventral border of the orbit ti®ed. The quadrate is straight and is more together with the lacrimal. The posterodorsal slender than in Anchaurosaurus gilmorei. process forms the posterior bar of the orbit The cephalic condyle expands strongly me- and dorsally contacts the postorbital. dioposteriorly to form a triangular table and PALATAL ELEMENTS: All of the palatal el- has a well-developed foramen penetrating its ements are toothless (®g. 7D). Better pre- dorsal surface. The anterolateral surface of served on the right side than the left, the vo- the quadrate is smooth and slightly convex. mers are paired and slightly elongate. The The quadrate foramen opens above the ven- palatines are wide, but have no midline con- tral condyle on this surface. However, the an- tact. The suborbital fenestra is slightly elon- teromedial surface is strongly concave to gate, extending to the midlevel of the pala- form a wide and vertical groove dorsal to the tine. The fenestra is medially bordered by the ventral condyle. In lateral view, the tympanic palatine and the pterygoid, and is laterally crest is thin, straight, and vertical. The tym- bordered by the maxilla and the ectoptery- panic crest is oriented at a 90Њ angle to the goid. The ectopterygoid in palatal view has horizontal lateral border of the cephalic con- a triangular base, which is sutured medially dyle, giving the lateral crest for the tympanic with the widened pterygoid, and has a ven- membrane an L-shape. The posterior surface tral process forming small part of the weakly of the quadrate is divided into two surfaces developed pterygoid ¯ange. The ectoptery- by a vertical posterior crest, which is weakly goid forms the posterior border of the sub- arched anteriorly. The lateral part is strongly orbital fenestra, and the anterolateral process concave to form a deep fossa, and the medial extends to the midlevel of the suborbital fe- part is slightly concave and forms an inverted nestra. The pterygoid has an elongate pala- triangular-shaped surface as the medial crest tine process, which thins anteriorly and is su- diminishes ventrally. The posterior opening tured to the palatine along its medial edge to of the quadrate foramen penetrates the me- form the medial border of the interpterygoid dial surface on the lower one third of the vacuity. The posterior part of the process bone, close to the posterior crest. The ventral broadens and has an oblique lateral edge for condyle is transversely expanded and is sad- articulation with the palatine. The posterior dle-shaped with a concave ventral surface. edge of the lateral process in¯ects dorsally to The right epipterygoid is preserved and ex- form the pterygoid ¯ange. The quadrate pro- posed in dorsal view (®g. 7C). It attaches to cess is essentially a blade that is convex lat- the lateral surface of the prootic, but its con- erally and concave medially. Like in many tact with the parietal cannot be con®dently other iguanians, a notch is developed medi- determined as the bone may have been ally at the base of the process that forms the slightly displaced posteriorly. joint with the basipterygoid process of the Only the left maxilla is preserved, and it basisphenoid. The posterior extremity of the is incomplete. It has a low dorsal process that process becomes a slender blade, attaching bends medially to contact the nasal, prefron- to the medial border of the quadrate. tal, and the anterolateral process of the fron- BRAINCASE: The basisphenoid and the ba- tal. The posterior border of the process is sioccipital form the braincase ¯oor. These el- notched for a well-developed lacrimal. The ements are unfused and separated by a clear posterior process of the maxilla has a nearly suture (®g. 7D). The base of the rostrum of transverse suture with the jugal, and in this the basisphenoid is slightly thickened, and aspect differs from Anchaurosaurus gilmorei has a small depression posterior to it. An- (see Gao and Hou, 1995: ®g. 1). The maxilla terolaterally, the basipterygoid process is has 18 well-preserved teeth, and probably short, but has a strongly expanded condyle four to ®ve additional anterior teeth are miss- directed anterolaterally at a 45Њ angle to the ing owing to breakage (see below). midline. Posterolaterally, the basisphenoid The jugal is broken on the left side, but a bears a short process attaching to the ventral 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 29 surface of the basioccipital and extending to lateral view, the dentary has a smooth surface the base of the spheno-occipital tubercle. The and carries seven mental foramina. The last fo- basioccipital forms the posterior part of the ramen is located at the midlevel of the tooth ¯oor and ventral part of the lateral wall of row. Like in Anchaurosaurus gilmorei (Gao the braincase, and a major part of the occip- and Hou, 1995), the dentary is posteriorly bi- ital condyle. furcated and notched for the blunt surangular, Dorsolateral to the ¯oor of the braincase, with little involvement of the angular bone. the recessus vena jugularis is well preserved The posterodorsal (coronoid) process is shorter on both sides of the holotype. The lateral but stronger than the posteroventral (Meckeli- wall of the recessus is formed by the prootic an) process, which extends on the ventral bor- with a sharp crest (crista prootica), but the der of the jaw and wedges between the sur- medial wall is formed by three elements: dor- angular and the angular. The coronoid has a sally by the prootic and ventrally by the ba- lightly built dorsal process, the lateral surface sisphenoid and basioccipital. A posterior of which carries a vertical crest for the external opening of the Vidian canal penetrates the jaw adductor. This crest ventrally ends with a medial wall of the recessus. It opens between prominent process. This condition is different the base of the basipterygoid process and the in Anchaurosaurus gilmorei, where the coro- basisphenoid-basioccipital suture, with no in- noid process is robust, lacks a vertical crest, volvement from the prootic. A small facial but has a low and robust tubercle. Like in An- foramen penetrates the prootic and opens on chaurosaurus gilmorei, the coronoid of the the medial wall of the recessus. The foot of new species has no lateral blade, but a small the right stapes as preserved covers the fo- wedge between the dentary and the surangular. ramen ovale, but the shaft is not preserved. The surangular occupies most of the post- The foramen ovale is located dorsal to the dentary part of the jaw in lateral view. It has occipital recess. A slender bone extends pos- a large lateral surface and a prominent crest teriorly from the occipital recess. Although for the attachment of the jaw adductor muscle. similar in position to the stapes, it is long and As in Anchaurosaurus gilmorei, the anterior slightly curved, indicating it is a dislocated surangular foramen is located in a low position hyoid element. Another hyoid element is pre- anteriorly in the middle of the bone, and the served on the left side posteroventral to the posterior surangular foramen opens on the braincase ¯oor. crest posteriorly near the craniomandibular Most of the occipital aspect of the skull is joint (®g. 7A, B). The angular is incompletely not exposed, because the skull is articulated preserved on the left side, and left clear im- with several . However, some pressions on the right. This element is small features of the occiput can be observed from and barely exposed in lateral view. It wedges dorsal and ventral views. In dorsal view, the between the surangular and the prearticular in supraoccipital carries a weakly developed me- ventral view and between the dentary and the dian crest for attachment of the ligamentum splenial in medial view. The angular foramen nuchae (Oelrich, 1956). Laterally parallel to (preserved on the left side) is extremely small, the crest, the posterior semicircular canal and opens on the medial side of the jaw close swells dorsally, but no suture can be delimited to the posterior end of the splenial. The prear- between the supraoccipital and the exoccipital. ticular (fused with the articular) is the second In ventral view, the paroccipital process is largest element of the postdentary part of the shorter than in Anchaurosaurus gilmorei and jaw. Its contact with the surangular and the extends more laterally than posteriorly. The ®s- posteroventral process of the dentary is ex- surelike vagus foramen (for cranial nerves X, posed, as the angular bone that normally cov- XI) and the rounded hypoglossal foramen (for ers this suture is not preserved. The prearticu- cranial nerve XII) are very close to one anoth- lar medially carries a prominent and slightly er, and are both located dorsolateral to the oc- hooked angular process, and a posteriorly di- cipital condyle. rected retroarticular process. The articular fossa MANDIBLE: The mandibles are well pre- for the mandibular joint with the quadrate con- served on both sides, with slight damage to the dyle lacks an anterior or posterior buttress, right coronoid and the postdentary region. In therefore, the joint seems to be more freely 30 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249 movable. Posterior to the jaw joint, the retroar- and has a low but well-developed crown, ticular process is weakly developed and pos- which extends posteriorly and overlaps part teriorly directed. The dorsal surface of the pro- of the third cervical. Each of the cervicals cess is concave, but has no foramina opening has a well-de®ned ventral keel. in it. Several caudals are preserved in associa- In medial view, the anterior three-fourths of tion with the skull. Two anterior caudals are the Meckelian canal is closed, without fusion dislocated to the left orbit, and each of these of the dentary tube. The anterior end opens shows an fracture posterior to a near the symphysis. The posterior one fourth single pair of transverse process. This con- of the canal is medially covered by a greatly dition corresponds with the so-called ``Sce- reduced splenial, which has its posterior exten- loporus-type'' of caudal autotomy as de- sion terminating anterior to the angular fora- scribed by Etheridge (1967). men. The anterior process of the surangular ex- tends and wedges between the splenial and the COMPARISON AND DISCUSSION anteroventral process of the coronoid. The dor- sal rim of the surangular is anteriorly rounded The new taxon shares several characters as commonly seen in other lizards, but poste- with Anchaurosaurus gilmorei including: riorly a distinct ¯ange is strongly developed skull elongate with relatively pointed snout; anteromedial to the craniomandibular joint and parietal table trapezoidal, but with long, slen- above the mandibular fossa (®g. 7C). Such a der supratemporal process; parietal foramen strong ¯ange is absent in other lizards. Func- opens at the frontoparietal suture, but is en- tionally, this ¯ange may serve as an insertion larged on the parietal side. These indicate a of the pterygomandibularis muscle (see Oel- close relationship of the two forms. However, rich, 1956). Also different from Anchaurosau- Zapsosaurus sceliphros is clearly distin- rus gilmorei (see Gao and Hou, 1995: ®g. 1), guishable from Anchaurosaurus gilmorei by the mandibular fossa in Zapsosaurus sceli- the characters listed in the diagnosis. phros is strongly reduced into a short and shal- Both Zapsosaurus sceliphros and Anchau- low groove, extending only to the midpoint be- rosaurus gilmorei are relatively large lizards tween the coronoid process and the cranioman- dibular joint. in comparison with other Cretaceous iguani- ans known from the Gobi. These taxa are DENTITION: The morphology of the mar- ginal teeth is best observed on the incom- from the same geological formation (Dja- plete left maxilla, which has 18 tricuspid dokhta Formation), but do not co-occur at the teeth preserved. The teeth are much shorter same localities. Anchaurosaurus gilmorei is and more slender than in Anchaurosaurus known from Bayan Mandahu near the south- gilmorei, and the crowns are more strongly ern border of the Gobi, and Zapsosaurus sce- ¯ared, having the small lateral cusp separated liphros from the Tugrugeen Shireh locality, from the prominent central cusp by a clearly which is some 400 km northwest of the for- de®ned groove (®g. 7A). Owing to breakage mer locality. of the maxilla, a complete tooth count of the Although Gao and Hou (1995) noted that upper dentition cannot be obtained, but can Anchaurosaurus gilmorei shares 11 character be estimated at 23±24 teeth. The right den- states with crotaphytines, the relationships of tary contains 27 positions for the complete Anchaurosaurus gilmorei and Zapsosaurus tooth row, and these are all tricuspid except sceliphros to other iguanians are unclear. Al- for the anteriormost ®ve that are unicuspid. ifanov (1996) classi®ed Anchaurosaurus in The number and morphology of the premax- the together with the illary teeth cannot be determined. Arretosaurus Gilmore, 1943. Examination of VERTEBRAE: On the holotype (IGM 3/71), the known material of Arretosaurus, includ- the ®rst three cervicals (the atlas- com- ing the holotype (AMNH 6706), indicates no plex and the third ) and part of the shared derived character states supporting the fourth are preserved in articulation. The atlas grouping of these taxa in the same family. is a simple ringlike structure, the elements of Until a thorough study of the phylogenetic which remain unfused. The axis is elongate relationships of the Gobi and other basal ig- 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 31

Fig. 8. Polrussia mongoliensis: A±C, IGM 3/73, incomplete skull articulated with mandibles and cervical vertebrae, dorsal, ventral, and lateral views. uanians is completed, the interrelationships other nonacrodontan iguanians by the fol- of several nonacrodontan iguanians including lowing derived character states: frontals slen- Anchaurosaurus and Zapsosaurus remain derly elongate and strongly narrowed; unclear. spheno-occipital tubercle greatly reduced as remnant knob; splenial retracted to slightly Polrussia mongoliensis anterior to posterior end of tooth row; Meck- Borsuk-Bialynicka and Alifanov, 1991 elian canal entirely closed by fusion of den- Figure 8 tary tube; posterior extension of dentary ter- HOLOTYPE: ZPAL MgR-I/119, incomplete minates at level of dorsal process of coro- skull with mandibles. noid; marginal teeth having slenderly cylin- TYPE LOCALITY AND HORIZON: Khulsan, drical shafts and pointedly unicuspid crowns. Nemegt Basin, Mongolia; Upper Cretaceous REFERRED SPECIMEN: IGM 3/73 (MAE . 219/92-45), partial skull with mandibles and KNOWN DISTRIBUTION: Known only from cervical vertebrae; collected from Khulsan. the type locality and horizon. REMARKS: IGM 3/73 is referred to Polrus- REVISED DIAGNOSIS: Distinguished from sia mongoliensis based on several diagnostic 32 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249 features of the species shown on the speci- milial level subgroups: the Agamidae* and men: the splenial is retracted to slightly an- the Chamaeleonidae, with the latter subgroup terior to the posterior end of the dentary being considered to be the ``offshoots of tooth row; the Meckelian canal is entirely agamid stock'' (Camp, 1923). The monophy- closed by fusion of the dentary tube; poste- ly of the Chamaeleonidae is well supported rior extension of the dentary terminates at the (Estes et al., 1988; Frost and Etheridge, level of the coronoid dorsal process; and the 1989), but monophyly of the Agamidae* is marginal teeth are slenderly built, with point- uncertain (Frost and Etheridge, 1989). ed, unicuspid crowns. Several lizard taxa from the Gobi Desert Although fragmentary, IGM 3/73 is only as described below are tentatively placed in the second specimen (other than the holo- the Acrodonta, as they all have den- type) known for the species. The new spec- tition; however, they seem to form a mono- imen reveals some unknown morphology phyletic clade (see below) that may not be and clari®es some uncertainties about the part of the crown-group Acrodonta. A thor- species. The con®guration of the parietal is ough phylogenetic analysis with incorpora- uncertain on the holotype, but the new spec- tion of these Gobi taxa is badly needed, and imen shows the element is rectangular and following the results of such an analysis, cur- has an unossi®ed region indicating a fonta- rent classi®cation of the acrodontan lizards nelle. In palatal view, the new specimen may have to be revised. shows no midline contact of the palatines, contrary to the speculation ``judging from the PRISCAGAMINAE BORSUK-BIALYNICKA AND position of the right bone'' on the holotype MOODY, 1984 (Borsuk-Bialynicka and Alifanov, 1991: 338). Also from the new specimen, the pter- The Priscagaminae are a group of acro- ygoid teeth are retained, but palatine teeth are dontan iguanians known from the Upper Cre- absent. The spheno-occipital tubercle is taceous deposits in the Gobi Desert. The greatly reduced into a small knob. group includes Mimeosaurus, Priscagama, Regarding the relationships of Polrussia Phrynosomimus, and possibly - mongoliensis, Borsuk-Bialynicka and Alifan- gama (see Alifanov, 1996 for different clas- ov (1991: 340) stated that ``on the basis of si®cation of these taxa). The possible mono- the present knowledge the , non- phyly of the group is supported by the fol- anole Polychridae, Tropidurinae and Leioce- lowing potential synapomorphies: dermal phalinae may not be excluded as possible rel- roof elements of skull ornamented with atives of Polrussia.'' It is worth noting, how- small, rounded tubercles (Borsuk-Bialynicka ever, that Polrussia mongoliensis shares with and Moody, 1984); lateral coronoid process Igua minuta at least one character state: the present as platelike and ventrally extended parietal is rectangular with a large fontanel. ¯ap (Borsuk-Bialynicka and Moody, 1984; Pending an actual phylogenetic analysis, this Gao and Hou, 1995); both anterior and pos- character state may indicate a closer relation- terior mylohyoid foramina present on medial ship of the two species. side of jaw (Borsuk-Bialynicka and Moody, 1984). ACRODONTA COPE, 1864 Mimeosaurus crassus Gilmore, 1943 DEFINITION: The most recent common an- Figure 9 cestor of extant Agamidae* and Chamae- leonidae and all of its descendants (Estes et HOLOTYPE: AMNH 6655, left maxilla al., 1988; see Frost and Etheridge, 1989; see fused with jugal. also remarks below). TYPE LOCALITY AND HORIZON: Bayn Dzak DIAGNOSIS: The Acrodonta as above de- (Shabarakh Usu), Mongolian Gobi Desert; ®ned can be diagnosed by some 13 derived Upper Cretaceous Djadokhta Formation (see character states (see Estes et al., 1988 for list Gilmore, 1943). of characters and citations). KNOWN DISTRIBUTION: Bayn Dzak, Ukhaa REMARKS: The Acrodonta include two fa- Tolgod, Zos Wash, Bayan Mandahu localities 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 33

(Gilmore, 1943; Gao and Hou, 1996; this pa- per); Djadokhta Formation. REVISED DIAGNOSIS: Distinguished from other acrodontan iguanians by having the fol- lowing derived character states: strong re- duction of premaxilla; maxilla short, deep, and subrectangular in fusion with jugal; max- illary tooth row short, straight, with ®rst two teeth conspicuously enlarged and caninelike; lateral process of coronoid ¯attened with dis- tinct vertical crest anteriorly. REFERRED SPECIMENS: IGM 3/74 (MAE 83/ 93-89), IGM 3/75 (MAE 63/93-153); both incomplete skulls with mandibles and both from Ukhaa Tolgod. IGM 3/76 (MAE 96- 105), incomplete skull with mandibles from the Zos Wash locality. REMARKS: Although known since the 1940s, only a few well-preserved skulls of Mimeosaurus crassus have been collected. The new specimens from Ukhaa Tolgod and the adjacent Zos Wash locality, together with those collected from Bayan Mandahu (Gao and Hou, 1995), consistently display a unique set of characters. We emend the spe- cies diagnosis, accordingly (see above). The new specimens reveal important new information about the skull morphology and dentition of this iguanian species. Well-pre- served skulls (e.g., IGM 3/76 from Zos Wash) show a remnant postfrontal hidden be- neath the posterior rim of the orbit (®g. 9A). Comparison with the holotype (AMNH 6655) not only con®rms the referral of these new specimens to this taxon, but also reveals that this lizard had a conspicuously heter- odont dentition. As Gilmore (1943) original- ly described, the ®rst two maxillary teeth are enlarged and caninelike, with the second be- ing the largest; however, some specimens (e.g., IGM 3/75, 3/76; see ®g. 9C, D) show that this type of heterodonty is more con- spicuous than others (the anterior dentary teeth are strongly protruding anterior to the

← Fig. 9. Mimeosaurus crassus: A±C, IGM 3/ 76, incomplete skull with mandibles from Zos Wash, dorsal, ventral and lateral views; D, IGM 3/75, fragmentary skull with mandibles from Ukhaa Tolgod, right lateral view. 34 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249 premaxilla), suggesting that the variants may Bialynicka and Moody, 1984; Gao and Hou, represent different sexes. 1996; this paper). Based on a single very fragmentary skull REVISED DIAGNOSIS: Distinguished from (PIN No. 3143/102) from Tugrugeen Shireh other acrodontan iguanians including Mimeo- (Tugrikin-Shireh) in the Djadokhta Forma- saurus crassus by the following derived tion, Alifanov (1989a) named a second spe- character states: skull lightly built, and ¯at- cies, Mimeosaurus tugrikinensis, but provid- tened; pointed snout elongate; dorsal process ed no evidence by which it can be distin- of maxilla close to midpoint of tooth row, guished from the type species. Gao and Hou with anterior extension of maxilla; basipter- (1995) questioned the validity of the nominal ygoid process of basisphenoid asymmetrical- species (M. tugrikinensis) and treated it as a ly widened, having strong posterolateral ex- subjective junior of Mimeosaurus tension; lower jaw elongate, angular process crassus (see Alifanov, 1996 for different reduced as slender spike and hooked anteri- opinion). orly. Regarding the relationships and classi®- REFERRED SPECIMENS: IGM 3/77 (MAE 62/ cation of Mimeosaurus crassus, Alifanov 93-153), IGM 3/78 (120/93-93), both incom- (1996) grouped it with Gladidenagama in his plete skulls with mandibles from Ukhaa Tol- ``tribe Mimeosaurini,'' and classi®ed the god; IGM 3/79 (MAE 130), incomplete skull tribe in the (subfamily Pleu- with mandibles from Khulsan. rodontagaminae). The diagnosis of the tribe REMARKS: Besides the two specimens Mimeosaurini presented by Alifanov (1996) mentioned above, a much larger skull from is: ``process of tooth replacement ceases in Ukhaa Tolgod (IGM 3/80, MAE 307/93-162; postnatal period of ontogeny. Central point ®g. 10C, D) is referred to the same species of the jaw teeth expressed, with lateral with question. The anterodorsal part of this shelves. Posterior process of maxilla wide.'' skull is missing, but the lower jaws are com- Unfortunately, none of these character states plete. The mandible is elongate and curved are actually diagnostic of this group, and the as in Pleurodontagama aenigmatodes (see Mimeosaurini as de®ned by Alifanov is an Borsuk-Bialynicka and Moody, 1984), but arti®cial taxon. We lack access to Gladiden- the teeth (triangular and essentially acrodont) specimens, but we see no rationale are indistinguishable from Priscagama go- for placing Mimeosaurus in the Hoplocerci- biensis (see below). The lower jaw has 16± dae, which are a group of nonacrodontan ig- 18 teeth, in spite of elongation of the jaw. uanians commonly called the ``moruna- No signi®cant differences in skull mor- saurs.'' Morunasaurs have highly pleurodont phology have been found to distinguish Pleu- and multicuspid teeth (see Frost and Ether- rodontagama from Priscagama (Borsuk-Bi- idge, 1989), and this group bears no close alynicka and Moody, 1984). Discovery of the relationship with Mimeosaurus within the Ig- new specimen (IGM 3/80) further obscures uania. the two forms. In general, the two nominal taxa share character states such as an elon- Priscagama gobiensis gate antorbital part of the skull and a pointed Borsuk-Bialynicka and Moody, 1984 snout, the squamosal has a hooked postero- Figure 10 lateral process, the parietal foramen is sig- ni®cantly smaller than in Mimeosaurus and HOLOTYPE: ZPAL MgR-III/32, incomplete other related iguanians from the Gobi, and skull articulated with mandibles. the strongly reduced angular process has a TYPE LOCALITY AND HORIZON: Khermeen slender anteriorly hooked spike. However, Tsav, Mongolian Gobi Desert; Upper Creta- the very small sample size and the incom- ceous Barun Goyot Formation. pleteness of the available specimens do not KNOWN DISTRIBUTION: Barun Goyot For- allow determination whether the differences mationÐKhermeen Tsav and Khulsan; Dja- are an individual variant or phylogenetically dokhta FormationÐBayn Dzak, Bayan Man- signi®cant. Currently, differences in shape dahu, and Ukhaa Tolgod localities (Borsuk- and arrangement of the marginal teeth are the 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 35

Fig. 10. Priscagama gobiensis: A, B, IGM 3/77, incomplete skull with mandibles from Ukhaa Tolgod, dorsal and ventral views; C, D, IGM 3/80, incomplete skull with mandibles from Ukhaa Tolgod, dorsal and ventral views. 36 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249

Fig. 11. Phrynosomimus asper: A, B, IGM 3/81, nearly complete skull with mandibles (articulated with several vertebrae and partial pectoral girdle), dorsal and ventral views. only criteria on which the two forms can be al and supratemporal process of parietal; distinguished from one another. presence of robust lateral projection on jugal; anterior inferior alveolar foramen opens ven- Phrynosomimus asper Alifanov, 1996 tral to anteroventral process of coronoid at Figure 11 splenial-dentary suture; retroarticular process of mandible short and laterally compressed. HOLOTYPE: PIN No. 3142/318, nearly REFERRED SPECIMENS: IGM 3/81 (MAE complete skull with mandibles. [note: the ®g- 258/92-63), nearly complete skull with man- ure of the holotype is incorrectly inscribed in dibles from Khulsan (Area of Wall); IGM 3/ Alifanov (1996: ®g. 4); see discussion be- 82 (MAE 96-31), IGM 3/83 (MAE 152/93- low.] 40), both incomplete skulls with mandibles TYPE LOCALITY AND HORIZON: Khermeen Tsav locality; Upper Cretaceous Barun Goy- from Ukhaa Tolgod. ot Formation, Mongolian Gobi Desert. KNOWN DISTRIBUTION: Barun Goyot For- DESCRIPTION mationÐKhermeen Tsav and Khulsan local- ities; Djadokhta FormationÐUkhaa Tolgod. The three specimens listed above represent DIAGNOSIS: Sharing with other acrodontan the only material known for the species other iguanians derived characters such as absence than the holotype. Notably they were not col- of postfrontal, and acrodont dentition on lected at the type locality Khermeen Tsav. main part of marginal tooth row. Distin- Among these newly recovered specimens, guished from other acrodontans including IGM 3/81 (®g. 11) consists of a nearly com- Mimeosaurus in having the following auta- plete skull with mandibles, several articulat- pomorphies: skull short and equilaterally tri- ed vertebrae and a partial pectoral girdle. Al- angular; presence of prominent bony spikes though the skull is dorsoventrally com- on squamosal and parietal; loss of lateral pro- pressed, all the elements are in articulation cess of squamosal; well-developed medial and show no signi®cant damage. A descrip- process of squamosal separates supratempor- tion of this specimen is given below for bet- 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 37 ter understanding of the morphology of this below which is a well-developed down- bizarre acrodontan species. growth or ¯ange that has a depression on SKULL ROOF: The premaxilla is a single each side for insertion of the axial muscles. bone with a short and wide spine projecting The prefrontal is slightly enlarged, but posterodorsally. The spine slightly separates lacking a hooked lateral process as seen in the nasals anteriorly. The slightly distorted Phrynosoma. The dorsal part of the prefron- tooth-bearing border of the premaxilla is not tal forms a small triangular shelf roo®ng the exposed, and the number of premaxillary anteromedial corner of the orbit, and is or- teeth cannot be determined. However, it can namented with small bony knobs like other be observed that the tooth-bearing part of the roo®ng elements. Extending close to the bone is only slightly wider than the spine. midlevel of the orbit, the frontal process of The nasals are short and paired, with a the bone is proportionally much more slender clear midline suture. A lateral process of the than in Priscagama and Mimeosaurus.A nasal forms the posterior border of the narial much stronger anteroventral process forms opening, and contacts both the prefrontal and the anterior wall of the orbit and ventrally the dorsal process of the maxilla. The fron- contacts the palatine. Laterally at the corner tals are fused and are constricted between the of the orbit, a minute bone represents the orbits as in other iguanians. The frontals un- vestigial lacrimal. The lacrimal foramen is derlie the nasals anteriorly, and are exposed small, opening between the lacrimal and the anterolaterally with a slender spike interven- prefrontal. ing the nasal and the prefrontal. The spike is The maxilla is separated from the jugal, short, not reaching the maxilla; thus it does unlike the fused condition in Mimeosaurus not separate the nasal from contacting the (see below). With slight dislocation of the prefrontal. The posterior border of the fron- premaxilla, the right maxilla shows a well- tals widens to twice the width of the anterior developed anteromedial process extending to border, and has a transverse suture with the the midline. This extension indicates that the parietal. A proportionally large parietal fo- maxillae were in contact behind the premax- ramen opens at the frontoparietal suture. The illary spine (an acrodontan condition, Estes subolfactory ¯ange (crista cranii) is weakly et al., 1988; but see discussion above). Like developed as a low curb forming a trough in Mimeosaurus, several small and rounded for the olfactory tract. The dorsal surface is tubercles are developed along the ventral ornamented with small bony knobs. border of the orbit and the posterodorsal pro- The parietal table is trapezoidal, having a cess of the jugal. The latter bone has a very strongly widened anterior border and a much prominent tubercle projecting laterally at the narrower posterior width (®g. 11A). This posteroventral corner of the bone, but it lacks con®guration is different from Phrynosoma, the hooked posteroventral process seen in in which the table is generally rectangular some extant acrodontans. (see Etheridge, 1964: ®g. 2). The dorsal sur- The postfrontal is lost, and the postorbital face of the parietal table is ornamented with is the sole element separating the orbit from small bony knobs around the parietal fora- the supratemporal fenestra. Although boom- men, but the most prominent ones are located erang-shaped in dorsal view, this element is at the base of the supratemporal process. The triradiate: it has a medial process sutured supratemporal process is very slender, and it with the posterolateral process of the frontal, extends laterally behind the medial process a weak anterolateral process articulated with of the squamosal and ®ts in a groovelike fac- the jugal, and a much stronger posterolateral et of the latter element. This pattern of artic- process articulated with the squamosal. ulation of the two elements is different from The squamosal is the most characteristic Phrynosoma in which the two processes di- element of this species, which has four prom- rectly abut (see e.g., Etheridge, 1964: ®g. 2). inent spikes along its posterior and lateral In Phrynosomimus asper, the supratemporal borders. The bone is curved medially, form- process of the parietal does not contact the ing most of the posterior and lateral borders quadrate. The posterior border of the parietal of the rounded supratemporal fenestra. The table is formed as a sharp and curved ridge, squamosal lacks a lateral process, and in this 38 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249 respect differs from Priscagama and Mimeo- and it penetrates the prootic bone. Posteriorly saurus, in which the same element is trira- in the recessus, the foramen ovale is identi- diate with prominent lateral processes. Lat- ®able as an opening anterior to the occipital eral to the postorbital, the squamosal contacts recess. Slightly anterior to the foramen ovale the jugal as generally seen in other iguanians. is the facial foramen, which is very small and Both quadrates are well preserved. The opens posteriorly. quadrate is slender and vertically straight. MANDIBLE: Mandibles on both sides are Dorsally, the slightly expanded cephalic con- preserved and anteriorly articulated at the dyle contacts both the squamosal and the par- symphysis. In keeping with the proportions occipital process but lacks a contact with the of the skull, the mandibles are short and slen- supratemporal process of the parietal. The der. In lateral view, the dentary has a poster- supratemporal is incompletely preserved on oventral extension terminated at the level of both sides. The articulation pattern of the su- the last tooth position, but its posterodorsal pratemporal with the squamosal and the pa- articulation with the coronoid is obscured by rietal cannot be ascertained, although an ar- the upper jaw as preserved. The surangular ticular surface on the supratemporal process is poorly preserved on both sides. The po- of the parietal indicates that the supratem- sition of the anterior surangular foramen can- poral may approach the base of the process. not be determined, but the posterior suran- PALATAL ELEMENTS: The vomers are short gular foramen can be identi®ed on the right and paired, having a sutural contact along the mandible. It is a large foramen in relation to midline (®g. 11B). The palatines are slightly the size of the jaw, and it opens far anter- widened, but are clearly separate and diverge oventrally from the craniomandibular joint. posteriorly for the interpterygoid vacuity The dentary medially forms a deep sub- (pyriform recess). Laterally each palatine has dental shelf, which has no dental gutter as in a short process that contacts the maxilla. The other acrodontans. The Meckelian canal is pterygoid has an elongate palatine process closed by the splenial, except for the anterior that is laterally sutured with the palatine and part which opens close to the symphysis. The anteriorly approaches (but does not seem to splenial is narrow and long, having an ante- contact) the vomer. It has a very short lateral rior extension terminating anteriorly at the process contacting the ectopterygoid behind level of one fourth of the length of the den- the suborbital fenestra, and a long and slen- tary tooth row. A small anterior mylohyoid der posterior process extending to contact the foramen penetrates the splenial, but the an- quadrate. The ectopterygoid forms the pos- terior inferior alveolar foramen opens at the terior border of the suborbital fenestra, and splenial-dentary suture at the level below the has a very prominent ventral process (pter- anteroventral process of the coronoid bone. ygoid ¯ange) for attachment of the pterygoi- The splenial has a tonguelike posterior ex- deus muscle. All the palatal elements are tension between the angular and the anterior toothless. process of the prearticular, and this extension BRAINCASE: In ventral view, the braincase terminates at a point anterior to the mandib- ¯oor is partly covered by a few dislocated ular fossa. In medial view, the coronoid is foot elements. The well-exposed middle part triradiate, lacking the posterodorsal process of the braincase ¯oor is largely formed by seen in extant acrodontans (e.g., Physigna- the basisphenoid (fused with the parasphe- thus, see Frost and Etheridge, 1989: ®g. 4). noid), whereas the basioccipital contributes The coronoid is not well preserved, but the to only the far posterior part of the braincase right side seems to show a lateral ¯ap as in ¯oor. The spheno-occipital tubercle is short Mimeosaurus and other priscagamines. The and ventrally directed, with a small occipital mandibular fossa is a narrow opening, ex- recess opening more posteriorly than later- tending posteriorly to the level above the an- ally. The crista prootica is poorly developed, gular process, which is very short and di- and thus the recessus vena jugularis is very rected anteromedially. Similar to the condi- shallow and lacks a well-de®ned lateral wall. tion in Phrynosoma (see Etheridge, 1964), Anteriorly within the recessus, a posterior the retroarticular process is laterally com- opening of the Vidian canal is identi®able pressed and vertical (®g. 11B). 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 39

DENTITION: Like in Mimeosaurus and squamosal. Small, triangular acrodont teeth many other acrodontans, the marginal teeth are also present. On the basis of these diag- in Phrynosomimus asper are triangular and nostic features, the three new specimens can acrodont. Due to slight distortion of the be con®dently identi®ed as Phrynosomimus snout, the premaxillary teeth are not ex- asper. As mentioned above, the new speci- posed, and thus the number and morphology mens represent the only material known for of the teeth on this element cannot be iden- the species other than the holotype. In addi- ti®ed. The right maxilla has eight teeth and tion, the discovery of two specimens (IGM probably two to three anterior ones are not 3/82, 3/83) from Ukhaa Tolgod extends the preserved, and anterior to the fourth tooth stratigraphic distribution of this peculiar ac- from the rear is a signi®cant space that may rodontan lizard from the type horizon (Barun indicate a tooth position; therefore, the com- Goyot Formation) to the Djadokhta Forma- plete maxillary tooth row may contain up to tion. 12 teeth. A problem stemming from the ambiguous The dentary teeth on both sides are en- description of the holotype specimen (PIN closed by the arch of the upper jaws, but in No. 3142/318) concerns its tooth count. Al- medial view the right mandible shows nine ifanov (1996) diagnosed the species as hav- teeth and probably three to four vacant po- ing a ``total of maxillary teeth no less than sitions; therefore, the complete dentary tooth 15; from which ®ve belong to the additional row probably contains 12±13 positions. The series,'' but later described it as having 17 teeth progressively increase in size towards (two caninelike teeth plus 15 postcanine the posterior end, and the three posteriormost teeth). Although described as having two teeth each have a resorption pit, indicating ``caninelike'' anterior teeth, none of the ®g- possible tooth replacement, although these ures that Alifanov provided actually show are essentially acrodont teeth. such teeth. Because the holotype is poorly PECTORAL GIRDLE: The preserved pectoral illustrated and incorrectly labeled, the actual girdle includes incomplete scapulae, cora- number of maxillary teeth cannot be ascer- coids, and an interclavicle. The tained for that specimen; however, if the low- ``T''-shaped interclavicle is slenderly built, er jaw (Alifanov, 1996: ®gs. 7f, o: showing differing from that in Phrynosoma which has seven positions on the posterior half of the the stem greatly reduced (see Etheridge, tooth row) is correctly illustrated, the max- 1964: ®g. 4). The clavicles on both sides are illary tooth count on the holotype may well in articulation with the interclavicle, al- have been overestimated. The best preserved though the right element is slightly displaced new specimen (IGM 3/81) shows only 11± posteriorly. The clavicle is basically boomer- 12 maxillary teeth. ang-shaped, having a small process (not The new specimen described above (IGM hooked) at its midpoint. Coracoid plates are 3/81) is preserved in light brown and poorly preserved on both sides, but the secondary cemented sandstones. The short triangular coracoid and its fenestra cannot be observed. skull with a spiked squamosal is strikingly Both left and right scapulae are incompletely similar to North American Phrynosoma, per- preserved, but show no signi®cant differenc- haps suggesting a similar burrowing life es from other known iguanians. style. The Gobi lizard, however, is clearly an acrodontan as evidenced by its triangular ac- COMPARISON AND DISCUSSION rodont teeth. Furthermore, the presence of small osteodermal tubercles on the skull roof Alifanov (1996) named and described and development of a lateral ¯ap of the cor- Phrynosomimus asper on the basis of a sin- onoid are indicative of a relationship with the gle specimen (PIN No. 3142/318), which is priscagamines. incorrectly labeled as ``(d) Gladidenagama The absence of a postfrontal is another semiplena, sp. nov. (holotype, PIN No. 3142/ character, besides the acrodont dentition, on 319)'' in his illustration (Alifanov, 1996: ®g. which this taxon is referred to the acrodon- 4). The new specimens display the same un- tans. All extant acrodontans have the post- usual skull con®guration with spikes on the frontal lost (Estes et al., 1988), although 40 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249 some fossil specimens (e.g., IGM 3/76: Mi- terior border lapping anterolateral border of meosaurus) retain a small bone. In addition, next posterior crown, last tooth much re- the loss of this element may be convergently duced. acquired in some nonacrodontan iguanians, REFERRED SPECIMENS: Ukhaa TolgodÐ including Phrynosoma, crotaphytines, most IGM 3/84 (MAE 96-113), nearly complete sceloporines, and oplurines (Etheridge and skull with mandibles; IGM 3/85±3/89 (MAE de Queiroz, 1988). 27/93-192, 42/93, 49/93-163, 161/93-40, and 94-16-1), all incomplete skulls with mandi- IGUANIA INCERTAE SEDIS bles. ZosÐIGM 3/90 (MAE 94-54), incom- plete skull with mandibles. Tugrugeen Shi- Isodontosaurus gracilis Gilmore, 1943 rehÐIGM 3/91 (MAE 261/92-123), nearly Figures 12, 13 complete skull with partial postcranial skel- HOLOTYPE: AMNH 6647, incomplete man- eton; IGM 3/92 (MAE 23/93-28), partial dibles with well-preserved teeth. skull with mandibles; IGM 3/93, 3/94 (MAE TYPE LOCALITY AND HORIZON: Bayn Dzak 221/93-8, 88/93-19), both partial skull with (Shabarakh Usu), Mongolian Gobi Desert; mandibles. Upper Cretaceous Djadokhta Formation. KNOWN DISTRIBUTION: Djadokhta Forma- DESCRIPTION tionÐBayn Dzak, Bayan Mandahu, Ukhaa Tolgod, Zos, and Tugrugeen Shireh localities The new specimens referred to Isodonto- (Gilmore, 1943; Alifanov, 1993a; Gao and saurus gracilis include the best preserved Hou, 1996; this paper). skulls known for the species, which reveal REVISED DIAGNOSIS: Sharing with other ig- taxonomically important features of this uanians the following derived character poorly known taxon. The species is previ- states: frontals fused and constricted between ously known mostly from tooth-bearing jaw orbits, presence of jugal/squamosal contact, material. In view of the fact that the skull parietal foramen opens at frontoparietal su- features of the species are extremely poorly ture, and presence of angular process in low- known, a description of the cranial morphol- er jaw. Differing from all acrodontan iguani- ogy is given below, based on the new ma- ans primarily in having highly pleurodont terial. dentition. SKULL ROOF: The premaxillae are fused, Distinguished from all nonacrodontan ig- bearing six conical teeth (IGM 3/85, 3/86, 3/ uanians by a large number of derived char- 91). The dorsal spine of the element is slen- acter states: squamosal signi®cantly widened der and elongate and is distally slightly spat- with lateral ¯ange; quadrate process of pter- ulate. The nasals are paired, having their an- ygoid strongly expanded and laterally com- terior one third intervened by the dorsal pressed as winglike; coronoid dorsal process spine of the premaxillae along the midline. not exposed laterally, but entirely covered by The lateral border of the nasal contacts both coronoid process of dentary; strongly devel- the maxilla and the prefrontal, as an antero- oped coronoid process of dentary carries lateral process of the frontal is not well de- prominent lateral crest for attachment of bod- veloped. Like in other iguanians generally, enaponeurosis of external mandibular adduc- the frontals are fused and constricted be- tor muscles; lateral surface of lower jaw de- tween the orbits. A frontal shelf (best shown velops distinct fossa below coronoid process on IGM 3/84, 3/92) is well developed ante- for the super®cialis of external mandibular riorly, and the shelf dorsally has a pair of adductor muscles; angular extends antero- depressions for the posterior processes of the medially to midlevel of dentary tooth row; nasals. The anterior part of each frontal is ventral border of lower jaw develops distinct slightly widened, and laterally has a ¯ange trochlear notch for M. pterygomandibularis; for articulation with the prefrontal (shown on marginal teeth reduced in number, containing IGM 3/84, 3/92; ®gs. 12A, 13C). The pos- no more than 14 maxillary and 16 dentary terior part of the element is very wide, with teeth; tooth crowns increasingly dilated pos- a maximum width three times that of the in- teriorly and compressed laterally, with pos- terorbital width. The frontoparietal suture is 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 41

Fig. 12. Iguania incertae sedis, Isodontosaurus gracilis: A±C, IGM 3/84, incomplete skull with mandibles from Ukhaa Tolgod, dorsal, ventral, and lateral views. 42 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249

Fig. 13. Iguania incertae sedis, Isodontosaurus gracilis: A, B, IGM 3/91, cranial part of a skeleton preserved in concretion from Tugrugeen Shireh, dorsal and left lateral views; C, D, IGM 3/92, incom- plete skull with mandibles from Tugrugeen Shireh, dorsal and ventral views. 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 43 simply transverse, but the posterior border of cess of the element is proportionally long, the frontal is slightly notched for the parietal extending to the midlevel of the orbit along foramen. the lateral border of the frontal. The ventral The parietal table is short and roughly process of the prefrontal (IGM 3/92) curves trapezoidal. A large part of the parietal table downward to form the anterior wall of the is penetrated by a well-developed fontanelle, orbit, and has a small notch on its lateral bor- which is con¯uent with the parietal foramen der for the lacrimal foramen; therefore, the (a feature also seen in several but not all oth- foramen must open at its suture with the lac- er nonacrodontan iguanians from the Gobi). rimal bone. The postfrontal is fused with the The lateral border of the parietal table is postorbital to form a postorbitofrontal (IGM ¯anged for origins of the temporal muscles. 3/84, 3/91), but one specimen (IGM 3/92) The posterior border of the table is also shows a remnant ``suture'' on the left ele- weakly ¯anged for attachment of the axial ment (no suture at all on the right side). muscles. The supratemporal process of the As mentioned above, the anteroventral parietal, best preserved on two specimens process of the jugal forms a large part of the from Tugrugeen Shireh (IGM 3/91, 3/92), is ventral border of the orbit, and it has a tri- slightly longer than the parietal table. For angular base that slightly bulges laterally. most of its length, the process carries a sharp The element, however, lacks a posteroventral dorsal crest and is sloped both medially and process. The posterodorsal process of the ju- laterally making the process roughly trian- gal strongly slants posteriorly, and the distal gular in cross-section. The process distally half of the process is spatulate contacting does not contact the quadrate, but is weakly both the postorbital and the squamosal (®gs. articulated with the squamosal and the su- 12A, 13B). pratemporal bone (see below). The squamosal (best preserved on IGM 3/ The maxilla is short, and is ®rmly articu- 91) is widened, with a lateral extension for lated to the lacrimal and jugal; these together the attachment of the temporal muscles. The form a roughly rectangular lateral wall of the lateral border of the wing is curved medially, skull below the orbit. The maxilla has a tri- and is posteriorly linked with a hooklike lat- angular posterior process bulging laterally. eral process. A large part of the squamosal This con®guration of the element is similar covers the cephalic head of the quadrate, but to that in Mimeosaurus crassus, but it is not its anterior extension curves laterally and ar- fused with the jugal and has no bony orna- ticulates with the jugal bone. The posterior mentation along its dorsal border. Anteriorly end of the squamosal carries a short but well- the maxilla bears a well-developed antero- de®ned dorsal (medial) process, forming the medial process (IGM 3/84, 3/85, 3/89, 3/91), posterior rim of the supratemporal fenestra which extends behind the premaxillary spine and contacting the supratemporal process of approaching or contacting the opposite struc- the parietal. The posterior border of the squa- ture. The nasal process of the maxilla is lo- mosal is slightly notched for articulation with cated dorsally above the anterior part of the the supratemporal bone (see below). tooth row. The process curves medially to No supratemporal bone is identi®ed on articulate with the nasal and prefrontal, but any of the known specimens of Isodontosau- seems to have no contact with the frontal as rus gracilis. Such an element is normally de- the anterolateral process of the latter is not veloped as a splint wedging between the su- well developed. Posterior to the nasal pro- pratemporal process of the parietal and the cess, the maxilla is dorsally articulated with squamosal (but see Frost and Etheridge, a small lacrimal and the entire length of the 1989). In this species, however, it appears to anterior process of the jugal; thus, the max- be absent as in some agamids and some other illa does not participate in the formation of lizards (see Estes et al., 1988 for citations). the ventral border of the orbit. The maxilla The quadrate is vertically positioned, with- of different individuals variably carries 10± out distortion (IGM 3/91). It has a thin and 14 teeth (see below). straight tympanic crest, lacking a strongly The prefrontal is well preserved on two concave conch on its posterior margin. The specimens (IGM 3/84, 3/91). The frontal pro- cephalic condyle is partially covered by the 44 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249 widened squamosal, but is exposed posteri- 13C). Also in dorsal view, the anterior and orly as a strong tubercle above the tympanic posterior semicircular canals are clearly rec- crest. As a matter of preservation, the ante- ognizable in several specimens. rior surface of the quadrate cannot be ob- The braincase ¯oor is slightly elongate and served without further preparation; but the rectangular in shape (exposed on IGM 3/84, posterior aspect of the bone is observable on 3/92). Anteriorly, the cultriform process of two specimens (IGM 3/91, 3/92). Like in the parasphenoid is poorly ossi®ed, as only many other lizards generally, the quadrate is the basal part is preserved. The basipterygoid posteriorly divided into two parts by a prom- process is short, having a slender shaft but inent and curved posterior crest that runs strongly expanded end for articulation with dorsoventrally from the cephalic condyle to the pterygoid. The basisphenoid/basioccipital the ventral condyle. The medial part of the suture is medially horizontal but laterally di- posterior aspect is about half the width of the agonal, a primitive condition (Gao and No- lateral part, and the medial part has a pos- rell, 1998). The basioccipital composes a terior opening of the quadrate foramen lo- smaller part of the braincase ¯oor than the cated about one third the height of the quad- basisphenoid. The spheno-occipital tubercles rate bone above the ventral condyle. The are short but proportionally quite robust. The ventral condyle does not show signi®cant ex- tubercles are more ventrally than laterally di- pansion, but remains small and slightly sad- rected. Other features of the braincase cannot dle-shaped ®tting in the articular fossa of the be observed without further preparation of lower jaw. the specimens. PALATAL ELEMENTS: Slightly displaced The epipterygoid is exposed on several palatal elements can be observed on IGM 3/ specimens (IGM 3/84, 3/85, 3/94). This is a 85 and 3/92 (®g. 13D). Both the palatine and slender pillar as seen in other lizards gener- pterygoid are toothless elements. The pala- ally, but its actual position and its contact tine is narrow and elongate, forming the me- with the lateral wall and roof of the braincase dial border of the suborbital fenestra. Along cannot be observed. the medial border of the palatine is a narrow MANDIBLE: The mandible of the species groove (on IGM 3/92), in which ®ts the slen- shows a set of peculiar features, which are der posterior process of the vomer which ap- apparently related to its specialized feeding proaches or may even contact the pterygoid. The pterygoid has a short anterior process, mechanism evidenced by its highly duropha- which is articulated to the medial edge of the gous dentition. The jaw is robustly built. The palatine. An even shorter lateral process ar- dentary portion is slightly longer than the ticulates with the ectopterygoid. The poste- postdentary portion. Posterodorsally the den- rior (or quadrate) process has a medial trough tary bears an extremely well-developed cor- as in other lizards generally, but the process onoid process, which entirely covers the lat- carries a strongly expanded dorsal wing. A eral surface of the dorsal process of the cor- similar condition is seen in extant onoid bone (leaving no lateral exposure of (Saksena, 1942: text-®g. 7). the latter element). This process carries a BRAINCASE: The supraoccipital is well ex- prominent lateral crest for insertion of the posed posterior to the parietal table (IGM 3/ bodenaponeurosis of the external mandibular 91, 3/92). It has a strongly convex dorsal sur- adductors (see Oelrich, 1956; Rieppel, face, but lacks a clearly de®ned sagittal crest, 1980c). The lateral surface of the mandible nor does it develop a processus ascendens at below this crest forms a distinct fossa (or de- its anterior border. The element laterally con- pression), providing extra surfaces for inser- tacts the prootic with a longitudinal suture, tion of the super®cialis portion of the exter- and posteromedially has a notch at the dorsal nal jaw adductor muscles (see Oelrich, rim of the foramen magnum. The posterolat- 1956). The fossa is ventrally bordered by a eral border of the bone contacts the exoccip- prominent adductor crest formed by both the ital with a slanted suture. The paroccipital surangular and the dentary bone. Within the process is short, and has the prootic extended fossa is the meandering dentary/surangular onto its anterolateral surface (®gs. 12A, suture, and the anterior surangular foramen 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 45 opens on the suture ventral to a short poste- ramen and the anterior mylohyoid foramen rior extension of the dentary (®g. 12C). lie closely together (IGM 3/84). The posterior surangular foramen is small DENTITION: As recognized by Gilmore and opens anterolateral to the craniomandi- (1943), Isodontosaurus gracilis is peculiar in bular joint. Below the anterior surangular fo- having a highly durophagous dentition. All ramen, the ventral border of the mandible de- the marginal teeth are highly pleurodont, velops a distinct trochlear notch probably for with approximately two thirds of the tooth a tendinous bundle of the pterygomandibu- shaft attached to a relatively deep lateral par- laris muscle (of Oelrich, 1956; M. pterygoi- apet of the jaw (®g. 13D). Tooth replacement deus of Lakjer, 1926; Haas, 1973). This is of the typical iguanid type, where new notch is formed largely by the angular, which teeth erupt within resorption pits. The tooth has a small lateral exposure and twists me- shafts are slender and slightly anteroposteri- dially at the trochlear notch. The retroarti- orly compressed; the crowns, however, are cular process is slender, posteriorly directed, strongly dilated anteroposteriorly and com- and terminates with a tubercle for the inser- pressed laterally, with posterior borders lap- tion of the M. depressor mandibularis (Oel- ping the outside of the next posterior crown. rich, 1956). Ventromedially at the base of the Generally, anterior teeth are small, increas- retroarticular process, an angular process is ingly becoming enlarged posteriorly; but the well developed and slightly hooked anteri- last maxillary tooth is often signi®cantly orly (®g. 12B). smaller than the adjacent anterior tooth. The The medial aspect of the mandible can be ultimate maxillary tooth is more medially lo- observed on two specimens (IGM 3/84, 3/ cated than others and is therefore slightly set 92). A noticeable feature on this side of the off from the main tooth line. jaw is the long anterior extension of the an- Both small and larger specimens show es- gular bone. The anterior extent is twice the sentially the same typical dentition; however, the number of teeth in a complete tooth row length of the posterior extension exposed on varies considerably among specimens. For the lateral surface of the jaw. Anteriorly the the maxillary tooth row, a complete tooth angular terminates at the midpoint of the count ranges from as few as ten teeth (IGM tooth row, anterior to the anterior inferior al- 3/89, 3/90) to as many as 14 (IGM 3/84, veolar foramen. This anterior extension has IGM 3/91, 3/94); two other specimens (IGM a long sutural contact with the splenial as in 3/85, 3/86) have 12 maxillary teeth on each some extant acrodontans (Jollie, 1960), but side. Dentary teeth can be observed on ®ve such a condition cannot be polarized satis- specimens (IGM 3/84, 3/85, 3/90±3/92), factorily in comparison with rhynchocepha- while other specimens have them concealed lians (Etheridge and de Queiroz, 1988; Frost by the upper dentition. A complete dentary and Etheridge, 1989). The posterior mylo- tooth row contains as few as 12 positions hyoid foramen (or angular foramen of other (IGM 3/90) or as many as 16 (IGM 3/84, 3/ authors) penetrates the angular at the level 91, 3/92). One specimen (IGM 3/85) has 14 slightly anterior to the coronoid summit of positions. Therefore, the dentary tooth row the jaw (®g. 13D). normally contains two more positions than The subdental shelf is present and curves the maxillary tooth row in the same speci- along the basal line of the tooth row; a sulcus men. dentalis (dental gutter), however, is com- pletely lost. The Meckelian canal anteriorly COMPARISON AND DISCUSSION turns ventrally and opens as a groove, but posteromedially is covered by the splenial Gilmore (1943) named Isodontosaurus and the angular bone. The splenial is just gracilis, and provisionally referred it to the slightly deeper than the angular and has a on the basis of its resemblance to posterior extension terminating at the level of in tooth morphology. Estes the distinct trochlear notch of the jaw where (1983) removed Isodontosaurus from the it contacts the anteroventral process of the Anguidae and hinted at a scincomorphan re- coronoid. The anterior inferior alveolar fo- lationship. Ignoring the fact that the species 46 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249 has a highly pleurodont dentition, Borsuk-Bi- ans, although the phylogenetic signi®cance alynicka (1991a) regarded Isodontosaurus of this character requires careful evaluation. gracilis as a ``true agamid,'' and Alifanov Several other peculiar features of Isodon- (1993a) formally classi®ed it in the Agami- tosaurus gracilis are detectable in its lower dae. The monotypic taxon has been given su- jaw, and may have developed in association bfamilial and familial ranks (Alifanov, with its specialized feeding mechanism. 1993a), which provide no help in elucidating These include: an unusually well-developed its relationships. coronoid process of the dentary that covers Several specimens (IGM 3/84, 3/91, 3/92), the entire lateral side of the coronoid bone collected from Ukhaa Tolgod and Tugrugeen with a prominent lateral crest for attachment Shireh localities, represent the best preserved of the bodenaponeurosis of external mandib- skulls known for Isodontosaurus gracilis. ular adductor muscles; the lateral surface of These specimens, together with several oth- the mandible has a well-developed fossa for ers, show character states that support the re- the super®cialis muscle; and the ventral bor- ferral of I. gracilis to the Iguania: frontals der of the mandible develops a distinct troch- are fused and constricted between orbits; lear notch that serves as a possible passage- presence of a jugal/squamosal contact; pari- way for a tendinous bundle of the pterygo- etal foramen opens at the frontoparietal su- mandibularis. ture (con¯uent with a fontanelle); and pres- Except for its pleurodont dentition, Iso- ence of an angular process on the mandible. dontosaurus gracilis shows striking similar- More importantly, the new specimens reveal ities in skull con®guration and palatal fea- several characters that were previously un- tures to extant Uromastyx, which is com- known for this lizard (see discussion below). monly placed in the Agamidae (or in Leiole- The peculiar dentition of this bizarre igu- pidinae of the Chamaeleonidae, Frost and anian was noted by Gilmore (1943), but a Etheridge, 1989). They share similarities such as: parietal foramen is con¯uent with comparison of the new specimens reveals the parietal fontanelle; jugal is posterodor- some previously unknown information. As sally spatulate; posterolateral process of ba- described above, the number of maxillary sisphenoid extends onto spheno-occipital tu- teeth ranges from as few as ten to as many bercle; dentary covers lateral part of the cor- as 14, and the number of dentary teeth ranges onoid process; angular strongly extends an- from 12 to 16. No clear pattern can be iden- teriorly to, or surpassing, midlevel of tooth ti®ed for correlation of size with number of row. However, these features must be care- teeth, as a higher number of teeth occurs in fully evaluated to determine whether they are both smaller and larger specimens. However, phylogenetically signi®cant. one recognizable pattern is that the dentary Based on the available evidence, Isodon- tooth row has two more positions than the tosaurus gracilis can be broadly referred to maxillary tooth row in the same individual. the Iguania. The relationships of this bizarre Besides the dentition, several other pecu- lizard within the Iguania, however, are far liar features of Isodontosaurus gracilis from clearly understood; and for this reason, should be noted. One of these is the presence we classify it as ``Iguania Incertae sedis.'' of a large parietal fontanelle con¯uent with the parietal foramen. A similar condition of GEKKOTA CUVIER, 1817 the foramen is known not only in some non- acrodontan iguanians from the Gobi (e.g., DEFINITION: The most recent common an- Anchaurosaurus, Zapsosaurus, Igua, and cestor of and and Polrussia), but also to a much smaller extent all of its descendants (Estes et al., 1988; see in some extant iguanians: e.g., Oplurus remarks below). (Blanc, 1977), some Sceloporus (Wiens and DIAGNOSIS: The Gekkota as above de®ned Reeder, 1997), and acrodontan Uromastyx can be diagnosed by as many as 46 derived (Beddard, 1905; El-Toubi, 1945; Jollie, character states (see Estes et al., 1988 for list 1960). Presence of such a fontanelle is a no- of synapomorphies and citations). ticeable feature for these Cretaceous iguani- REMARKS: Besides the Gekkonidae and 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 47

Pygopodidae, two fossil familial groups (Ar- fused and having descending processes in deosauridae and Bavarisauridae) are often contact below olfactory tract; postorbital ab- classi®ed in the Gekkota (Hoffstetter, 1964, sent; lacrimal lost; pterygoid teeth lost; crista 1966; Estes, 1983). However, recent studies prootica extends onto basipterygoid process; have shown that is possibly re- quadrate suspension by paroccipital abutting; lated to scincomorphs (Mateer, 1982; Evans, and retroarticular process de¯ected medially. 1993), and is not a gekkotan Differing from all other members of the but possibly related to either scincomorphs group in having the following autapomor- or anguimorphs (Evans, 1993, 1994). Eich- phies: Skull strongly elongate, having parie- staettisaurus is probably the best candidate tal table roughly equal length with frontals; for a gekkotan among the lizards presence of well-de®ned ventral process an- (see Evans, 1993 for discussion). The new teriorly on ventrolateral ¯ange of parietal; taxon described below is tentatively classi- supratemporal arch formed by slender squa- ®ed in the Gekkota, but resolution of its ac- mosal only; squamosal extends anteriorly to tual relationships with other known gekko- level of frontoparietal suture, and abutting ju- tans depends on future phylogenetic analyses gal; reduced number of small marginal teeth incorporating this fossil taxon. that are widely spaced and peglike. Although the monophyly of the Gekkota is highly corroborated by a long list of de- DESCRIPTION rived character states, the relationships of gekkotans to other major squamate groups The holotype (IGM 3/95) is the only are not unambiguous. Cladistic analysis by known specimen of this taxon. Although Estes et al. (1988) has shown a possible Gek- having a rounded snout, the skull is strongly kota- relation- elongate, and roughly rectangular in dorsal ship, but the monophyly of the latter taxon view. The snout is heavily covered with thick is weakly supported by as few as three pos- that have pitted surfaces, and the sible synapomorphies, none of which are un- external narial opening is not retracted. ambiguous (see Estes et al., 1988 for discus- SKULL ROOF: The premaxillae are fused sion). Various workers have advocated pos- and have a relatively wide dorsal spine that sible af®nities of the Gekkota with the Xan- forms the medial border of the narial open- tusiidae (see Rieppel, 1988 for review and ing. The spine is covered by a thick osteo- citations; see also Lee, 1998). Consequently, derm, and thus the pattern of the premaxilla- the relationships of the Gekkota within the nasal articulation cannot be observed. The Squamata merit further investigation. nasal is partly preserved on the left side, and is also covered with an , like the FAMILY INCERTAE SEDIS premaxillae. The frontals are fused (®g. 14B), and the olfactory ¯anges are well de- Myrmecodaptria microphagosa, veloped and in contact ventral to the olfac- new genus and species tory tract (gekkotan synapomorphy, see Estes Figure 14 et al., 1988). The frontal articulates anteriorly ETYMOLOGY: myrmex ϩ daptria (Gr., f.), with the nasal; other articulations are not pre- meaning anteater; mikrophagos (Gr.), mean- served. Posteriorly the frontal is expanded ing eating little. and has a straight transverse suture with the HOLOTYPE: IGM 3/95 (MAE 271/93-65), parietal. The dorsal surface of the frontal is incomplete skull with mandibles. scarred, suggesting a covering of osteoderms. TYPE LOCALITY AND HORIZON: Ukhaa Tol- The parietals are fused without a trace of god, Nemegt Basin, Mongolian Gobi Desert; a midline suture (®g. 14B). The parietal table Upper Cretaceous Djadokhta Formation is narrow and very elongate. In length, it is (Loope et al., 1998). roughly equivalent to the . The KNOWN DISTRIBUTION: Known only from dorsal surface of the parietal table is orna- the type locality and horizon. mented with osteoderms. The parietal fora- DIAGNOSIS: Sharing with other gekkotans men is a minute opening, which is located on derived character states such as: frontals the anterior one third of the parietal table. 48 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249

Fig. 14. Gekkota incertae sedis, Myrmecodaptria microphagosa, new genus and species: A±C, IGM 3/95 (holotype), incomplete skull with mandibles from Ukhaa Tolgod, left lateral, dorsal, and ventral views. 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 49

Fig. 14. Continued. 50 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249

The ventrolateral border of the parietal table entire bar of the supratemporal fenestra. The has a vertical ¯ange, indicating a ventral or- postfrontal (preserved on both sides) is igin of the temporal muscles. The anterior forked medially to clasp the frontoparietal part of the ¯ange bears a well-developed suture (see discussion above), and is laterally ventral process (downgrowth of Estes et al., articulated with both the jugal and the squa- 1988), which is laterally compressed and an- mosal (®g. 14B). teroposteriorly broadened. Such a process is The squamosal is a slender bar extending absent in extant gekkonids and pygopodids anteriorly to the level of the frontoparietal (Estes et al., 1988). The process ventrally suture, where it abuts the jugal and medially contacts the prootic (poorly preserved), but contacts the postorbital. The bone is hockey- it cannot be determined whether it contacts stick shaped without a trace of a dorsal pro- the epipterygoid, as the latter element is not cess. The squamosal has a short contact with preserved on either side of the skull. The su- the supratemporal process of the parietal pos- pratemporal process of the parietal is very terior to the supratemporal fenestra, but pos- short, having a length equal to about one teriorly this contact is separated by the splint- third that of the parietal table. The supratem- like supratemporal bone. poral process has a roughly triangular base The quadrate, preserved on both sides, is and a slender extension that contacts the par- in an oblique position slanting dorsoposter- occipital process (shown on the right side of iorly. As in extant gekkonids (Rieppel, the specimen). 1984), the quadrate has a convex anterior The maxilla has a very short anterior pro- slope that forms part of the origin for the cess articulating with the premaxillae (®g. external adductor muscles. The cephalic con- 14A). A slightly longer anteromedial process dyle dorsally articulates with the squamosal extends posterior to the tooth-bearing part of and the supratemporal, and medially bears a the premaxillae, but does not meet its equiv- well-de®ned process contacting the antero- alent counter part. The nasal (or dorsal) pro- ventral part of the paroccipital process (a cess of the maxilla is high, and is located gekkotan synapomorphy, see Rieppel, 1984; dorsal to the anterior half of the maxillary Estes et al., 1988). The medial border of the tooth row (a primitive condition in squa- quadrate is vertically straight, lacking any mates). The process dorsally articulates to trace of a pterygoid lappet. The ventral con- the nasal and the prefrontal, and may contact dyle is expanded transversely, and a small the anterolateral process of the frontal (indi- quadrate foramen is recognizable anteriorly cated by a gap between the nasal and the above the condyle. prefrontal). The lateral surface of the maxilla PALATAL ELEMENTS: In palatal view, the is covered with osteoderms, and is penetrated vomers and the palatines are disarticulated by a horizontal row of very small foramina and slightly displaced, indicating a reduced (lateral superior alveolar foramina) parallel contact between these elements (Rieppel, to its ventral border. The posterior process of 1984). The palatine is short, wide, and tooth- the maxilla forms the ventral border of the less. The anterior half of the pterygoid orbit, and extends to the midlevel of the orbit (toothless) is a broad elongate plate, making where it articulates with the jugal. the interpterygoid vacuity (pyriform recess) The dorsal surface of the prefrontal is narrow throughout most of its length. Al- small and triangular, and is ornamented with though incompletely preserved on both sides, osteoderms. The prefrontal forms the entire the quadrate process of the pterygoid is pro- anterior wall of the orbit, and ventrally con- portionally thick (®g. 14C). It is dorsally tacts the palatine within the orbit. Like in convex, but ventrally ¯attened. The ectopter- other gekkotans, the lacrimal is absent and a ygoid has a slender anterior extension, which small lacrimal foramen opens at the prefron- meets the palatine excluding the jugal and tal-maxilla suture (but see Rieppel, 1984). the maxilla from the suppressed suborbital Below the lacrimal foramen is another small fenestra. opening, representing the inferior orbital fo- BRAINCASE: The braincase on IGM 3/95 is ramen. The postorbital is completely lost, poorly preserved. In ventral view, the pre- leaving the elongate squamosal to form the served braincase ¯oor includes part of the 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 51 basisphenoid and part of the basioccipital well represent a primitive condition for squa- with the occipital condyle. The braincase mates. ¯oor is narrow and elongate, in keeping with In medial view, the splenial covers about the elongation of the skull. In articulation three fourths of the Meckelian canal below with several fragmentary bones including the tooth row. It has a slender tongue ex- part of the atlas vertebra, the occipital con- tending anteriorly, but posteriorly terminat- dyle, formed by the basioccipital and the ex- ing in front of the posteromedial process of occipital, is partially exposed in ventral view, the coronoid bone. The anterior inferior al- and seems to be rounded differing from the veolar foramen opens at the splenial-dentary bipartite condition in extant gekkotans (Riep- suture at the level of the anterior one third pel, 1984; Estes et al., 1988). of the tooth row, and the anterior mylohyoid The lateral wall of the braincase (prootic) foramen is close but slightly posteroventral is poorly preserved, but it shows an alar pro- to the former foramen. cess contacting the ventral process of the pa- Most of the postdentary part of the jaw is rietal. Although incompletely preserved, part formed by the surangular, which has a round- of the medial wall of the recessus vena ju- ed dorsal surface and a lateral crest for the gularis extends onto the basipterygoid pro- adductor muscles attached to the jaw. The cess, suggesting that the crista prootica may posterior surangular foramen opens anterior have extended forward to this point. In dor- to the craniomandibular joint and lateral to sal view, the supraoccipital is better pre- the buttress of the articular fossa. The suture served and anterodorsally bears a prominent line between the angular bone and its adja- process (processus ascendens; processus an- cent elements cannot be delimited, and thus, terior tecti of Jollie, 1960). Such a process is the of the angular is uncertain. Me- absent in extant gekkotans (Bellairs and Ka- dially, the mandibular fossa is narrow and mal, 1981; Rieppel, 1984; Estes et al., 1988). elongate, extending from the posteroventral Posterolaterally, the supraoccipital has a su- process of the coronoid to slightly anterior to tural articulation with the exoccipital, which the craniomandibular joint. The articular and forms most of the lateral border of the fora- the prearticular are fused without trace of su- men magnum, and is fused to the opisthotic ture. The retroarticular process of the jaw is forming the short paroccipital process. The broad at the base, but narrow toward the end exoccipital contributes to about one third of (as opposed to extant gekkotans). The retro- the occipital condyle on each side. articular process is slightly de¯ected medi- MANDIBLE: The mandibles are preserved ally resembling extant gekkotans, but differ- on both sides of the specimen. The articular ing from them in having no lateral notch. fossa of the lower jaw accepts the ventral DENTITION: The marginal teeth are strongly condyle of the quadrate, and has a prominent reduced both in size and in number. Most of buttress at its anterior border (®g. 14A). The the premaxillary teeth are not preserved, and dentary has a smooth lateral surface with no the number of teeth on this element cannot osteodermal ornamentation but a horizontal be determined, although it can be estimated row of small mental foramina. Posterodor- as six or seven. The maxillary and dentary sally, the dentary sutures with the coronoid teeth are peglike, widely spaced from one an- and the surangular, and at the junction of the other with no basal expansion at all. There three elements is a small opening represent- are approximately 13 tooth positions on each ing the surangular foramen. The dentary has maxilla, but the actual number cannot be de- a long posteroventral process extending far termined due to inadequate preservation. beyond the apex of the coronoid to the mid- The dentary teeth are better preserved than level of the surangular bone. Because such a those on the maxillae. The left dentary has long process occurs in some other gekkotans six teeth preserved, and the right side has and xantusiids (see Rieppel, 1984), in some ®ve, but a complete dentary tooth row prob- iguanians (Pregill, 1984; Etheridge and de ably contains about 15 positions on each side Queiroz, 1988; Frost and Etheridge, 1989), of the jaws. The teeth are pleurodont in terms and in more basal rhynchocephalians, it may of implantation, having about half of the 52 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249 tooth shaft attached to the lateral parapet of it is clear that the new lizard retains many the jaw. primitive character states in comparison to extant gekkotans. These include: retention of COMPARISON AND DISCUSSION a rudimentary parietal foramen; a well-de- veloped jugal that forms a complete postor- On the basis of the phylogenetic frame- bital bar; the retention of a supratemporal fe- work presented by Estes et al. (1988), two nestra with a complete upper temporal arch; subgroups are included in the Gekkota (but presence of a processus ascendens of the su- see Kluge, 1967 for different classi®cation): praoccipital; a well-developed supratemporal the Gekkonidae () and the Pygopodi- bone; Meckelian canal closed by the splenial dae ( lizards). The latter family in- without fusion of the dentary tube; splenial cludes about 30 species, which are con®ned extending beyond the midpoint of the den- to Australia and its neighboring islands (Mat- tary tooth row; retroarticular process that is tison, 1989). The group has a fossil record narrow posteriorly; and retroarticular process from Australia (Hutchinson, 1997), but is un- lacking a lateral notch, and thus, a narrow known from elsewhere. The former group, waist at the base of the process is not devel- Gekkonidae, includes more than 800 species, oped. Retention of these primitive character and has a distribution throughout the tropical states (see Estes et al., 1988 for character and subtropical world including hundreds of evaluation) suggests that the new species oceanic islands (Mattison, 1989). The group from the Gobi may well represent a phylo- has fossil records in both western genetically important basal taxon in the gek- and eastern hemispheres (see Estes, 1983), kotan clade. but the Mesozoic record of the Gekkonidae is extremely poor and is known only from SCINCOMORPHA CAMP, 1923 fragmentary specimens from the Gobi Desert DEFINITION: The most recent common an- (Alifanov, 1989b; Borsuk-Bialynicka, 1990). cestor of Scincoidea and , and all The referral of the new genus and species of its descendants (see Estes et al., 1988; see to the Gekkota is supported by several char- also Presch, 1988). acter states as mentioned above. However, DIAGNOSIS: The Scincomorpha as above the relationship of the new taxon within the de®ned can be diagnosed by nine synapo- Gekkota remains unknown in the absence of morphies (see Estes et al., 1988 for list of a phylogenetic analysis. In recent literature, synapomorphies and citations). there are considerable discussions regarding REMARKS: The Scincomorpha include six the higher level phylogeny of gekkotan extant familial groups (Scincidae, Cordyli- clades (Rieppel, 1984; Kluge, 1967, 1987; dae, Xantusiidae, , Teiidae, and Grismer, 1988; Estes et al., 1988), and con- ), the interrelationships ¯icting evidence from extant taxa has been of which are still matters of debate (see Estes the source of disagreement among authors on et al., 1988; Presch, 1988). Besides the extant the placement of the Pygopodidae and Eu- families, the Scincomorpha also include sev- blepharidae (see Estes et al., 1988 for com- eral fossil groups (, Poly- ments). It has been demonstrated that fossil glyphanodontidae, Macrocephalosauridae, evidence can overturn a phylogenetic hy- and Adamisauridae). Among these, the pothesis based only on extant groups (Gau- monophyly of the Paramacellodidae was re- thier et al., 1988; Kemp, 1988); therefore, in- viewed by Evans and Chure (1998), while corporating a primitive gekkotan from the the status of the other three groups is still Gobi (such as Myrmecodaptria micropha- problematic (see below). gosa) with extant taxa in a phylogenetic anal- ysis may provide important insights into the TEIIDAE GRAY, 1827 character evolution of the group as a whole and help resolve the differences among au- POLYGLYPHANODONTINAE GILMORE, 1942 thors. (Estes, 1983) Although the exact relationships of the Several taxa described below represent a new taxon cannot be ascertained at this , group of scincomorphs whose classi®cation 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 53 has been controversial. These taxa were placed in several different familial groups (Macrocephalosauridae, Polyglyphanodonti- dae, Adamisauridae, Teiidae) by different au- thors. More recently, Alifanov (1996) clas- si®ed these in the MacrocephalosauridaeÐa familial group the name of which was syn- onymized with Polyglyphanodontinae by Es- tes (1983). The monophyly of the Macroce- phalosauridae needs to be demonstrated be- fore the familial name can be validated; therefore, we tentatively follow Estes (1983) by placing these problematic taxa in the Po- lyglyphanodontinae (Teiidae).

Adamisaurus magnidentatus Sulimski, 1972 Figures 15, 16

HOLOTYPE: ZPAL MgR-II/80, incomplete skull with mandibles. TYPE LOCALITY AND HORIZON: Bayn Dzak, Mongolian Gobi Desert; Upper Cretaceous Djadokhta Formation. KNOWN DISTRIBUTION: Djadokhta Forma- tionÐBayn Dzak, Bayan Mandahu, and Tug- rugeen Shireh localities (Sulimski, 1972; Gao and Hou, 1996; this paper); Barun Goy- ot FormationÐKhermeen Tsav and Khulsan localities (Sulimski, 1978; this paper). REVISED DIAGNOSIS: A - tine differing from other members of the group in having the following derived char- acter states: premaxillary spine widened and spatulate; parietal anteromedially develops a rectangular tab overlapping frontals; parietal foramen opens close to frontoparietal suture but on parietal side; jugal expanded with en- larged posteroventral process; ectopterygoid signi®cantly enlarged, with robust ventral process; strong posterior extension of den- tary covering large part of surangular, and extending close to posterior surangular fora- men; posterior extension of angular bone sur- passing posterior surangular foramen and ter- Fig. 15. Scincomorpha, Teiidae (Polygly- minating below craniomandibular joint; mar- phanodontinae), Adamisaurus magnidentatus: A± ginal teeth strongly expanded and bulbous, C, IGM 3/116, nearly complete skull with man- subacrodont; replacement teeth emerge in dibles from Tugrugeen Shireh, dorsal, left and crypts below functional tooth row. right lateral views. REFERRED SPECIMENS: Ukhaa TolgodÐ IGM 3/96±3/101 (MAE 95-78, 31/93-164, 95-45, 94-10, 45/93-163, 48/93-163), all in- complete skulls with mandibles from Zo- phies Hill; IGM 3/102, 3/103 (MAE 32/93- 54 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249

Fig. 16. Adamisaurus magnidentatus: A±D, IGM 3/117, incomplete skull with mandibles from Tug- rugeen Shireh, dorsal, ventral, right and left lateral views; E, F, IGM 3/96, incomplete skull with mandibles from Ukhaa Tolgod, dorsal and lateral views. 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 55

91, 38/93-90), incomplete skulls with man- 3/117), however, undoubtedly show a much dibles from Small Exposure; IGM 3/104±3/ stronger posterior process covering a large 106 (MAE 117/93-93, 118/93-93, 122/ part of the lateral surface of the surangular 93-93), fragmentary skulls with mandibles bone and extending to the level of the pos- from Zo®a Exposure; IGM 3/107, 3/108 terior surangular foramen (®g. 15B, C). (MAE 449/93-124, 94-36), fragmentary skull Fourth, the angular bone was incorrectly re- with mandibles from First Strike; IGM 3/109 constracted as terminating far anterior to the (MAE 95-62), fragmentary skull with man- posterior surangular foramen (Sulimski, dibles from Camel Humps; IGM 3/110 1978: ®g. 1A; contra ®g. 1D, F), but well- (MAE 138/93-140), fragmentary skull with preserved specimens (IGM 2/116, 3/117) mandible from Camel Tits Hot Spot; IGM 3/ clearly show that the angular extends poste- 111±3/115 (MAE 64/93-45, 56/93-110, 119/ rior to the foramen and terminates at the lev- 93-93, 107/93-86, and MAE 23), fragmen- el of the craniomandibular joint. tary skulls with mandibles form Ukhaa Tol- Before its skull morphology can be clari- god without sublocality information. ®ed, the phylogenetic position of this bizarre Tugrugeen ShirehÐIGM 3/116, nearly lizard cannot be assessed satisfactorily. An complete skull with mandibles articulated extensive description of the skull osteology with partial postcranial skeleton; IGM 3/ based on well-preserved specimens and re- 117±3/122 (MAE 252/92-14, 18/93-2, 167/ assessment of the phylogenetic relationships 93-5, 168/93-5, 226/93-3, 227/93-27), all in- of this problematic taxon will be published complete skulls with mandibles. in a separate paper, but at this stage, we ten- Khermeen TsavÐIGM 3/123±3/125 tatively classify Adamisaurus in the Polygly- (MAE 196/92-25, 209/92-39, 211/92-39), all phanodontinae (Teiidae) as it apparently fragmentary skull with mandibles. shares many character states with Macroce- REMARKS: Sulimski (1972) ®rst described phalosaurus and Polyglyphanodon (Estes, and referred Adamisaurus magnidentatus to 1983). the ``?Agamidae,'' but later (Sulimski, 1978) erected a monotypic family (Adamisauridae) Gobinatus arenosus Alifanov, 1993 and placed it in the Scincomorpha. Estes Figures 17, 18 (1983) reviewed the available evidence and placed the species in the Polyglyphanodon- HOLOTYPE: PIN No. 3142/308, incomplete tinae, based on its shared similarities with skull with mandibles. macrocephalosaurs and Polyglyphanodon. TYPE LOCALITY AND HORIZON: Khermeen There is much confusion regarding the Tsav, Nemegt Basin, Mongolian Gobi De- cranial morphology of this lizard, and several sert; Upper Cretaceous Barun Goyot For- key sutures were incorrectly identi®ed. First, mation. the premaxilla was described as having only KNOWN DISTRIBUTION: Khermeen Tsav two teeth, but well-preserved specimens (Alifanov, 1993b); Khulsan and Ukhaa Tol- clearly show ®ve to six teeth (e.g., IGM 3/ god localities (this paper); Upper Cretaceous 116, 3/117). Second, the parietal foramen Barun Goyot and Djadokhta formations. was described and ®gured as opening at the REVISED DIAGNOSIS: Differing from other frontoparietal suture (Sulimski, 1972: ®g. 1, closely related scincomorphs in having the 1978: ®g. 1), but much better preserved new following derived character states: Skull specimens (e.g., IGM 3/99, 3/115, 3/116) strongly narrow and elongate; small osteo- show that the foramen penetrates the parietal, dermal ornamentation present on skull roof; which anteromedially develops a rectangular premaxillary spine elongate and spatulate; tab overlapping the frontals (®g. 15A). Third, basipterygoid process widened as short and the dentary was misinterpreted as having a roughly squared plate; ventral surface of shorter posterodorsal process overlapping the braincase ¯oor marked with three distinct de- lateral surface of the coronoid and a slightly pressions, one on basisphenoid and two on longer posteroventral process below the an- basioccipital; quadrate foramen present as terior surangular foramen (Sulimski, 1978: small pocket with three openings in it; pos- ®g. 1). The new specimens (e.g., IGM 3/116, terior border of angular bone slightly 56 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249

Fig. 17. Gobinatus arenosus: A±D, IGM 3/126, incomplete skull with mandibles from Khulsan, lateral, dorsal, and ventral views. 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 57

Fig. 18. Gobinatus arenosus: partial postcranial skeleton of IGM 3/126, in ventral view (anterior end towards right). notched; subdental shelf reduced and sulcus rior surface of the element is smooth and dentalis entirely lost; anterior inferior alveo- lacks any foramina (anterodorsal premaxil- lar foramen enlarged; angular extends to lev- lary foramina). The premaxillary spine is ex- el of posterior surangular foramen; retroarti- tremely elongate; it has a narrow shaft at the cular process slender and strictly directed base, but the distal part is spatulate (®g. posteriorly; marginal teeth bulbous but wide- 17C). The nasal process extends to such a ly spaced along tooth row; tooth crowns uni- posterior position that it separates the nasals cuspid and slightly recurved. for about half of their length along the mid- REFERRED SPECIMENS: KhulsanÐIGM 3/ line of the skull. 126 (MAE 61-91), nearly complete skull The nasals are paired. Each side of the el- with mandibles; IGM 3/127 (MAE 212/92- ement has a slender anterior process extend- 67), incomplete skull with partial right man- ing along the lateral border of the premaxil- dible. Ukhaa TolgodÐIGM 3/128 (MAE lary spine (nasal process of premaxilla), and 268/93-65), incomplete skull with mandibles. a short posterior process as a thin plate over- lapping the anterior shelf of the frontal. The DESCRIPTION nasal laterally contacts the dorsal process of Although slightly crushed dorsoventrally, the maxilla, and is well separated from the IGM 3/126 is the best preserved material prefrontal by an anterolateral process of the known for Gobinatus arenosus. This speci- frontal (scincomorph synapomorphy, see Es- men is described below, as it reveals impor- tes et al., 1988). tant features that are unknown from the ho- The frontals are paired, with a clear mid- lotype. line suture. The dorsal surface of the element SKULL ROOF: The premaxillae are fused as is ornamented with osteodermal rugosities, a single unit, which carries seven teeth (de- the complexity of which increases posteriorly termined from the broken bases). The ante- close to the frontoparietal suture. On IGM 3/ 58 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249

126, a short and shallow groove is seen pos- anterior opening of the superior alveolar ca- teriorly along the midline suture, but such a nal. The foramen is as large as the anterior- groove is not illustrated for the holotype (Al- most lateral superior alveolar foramen. ifanov, 1993b: ®g. 3), and the comparable The prefrontal is dorsally exposed as a tri- part on the referred specimens is either not angular table. It is anteriorly articulated with preserved (IGM 3/127) or damaged (IGM 3/ the dorsal process of the maxilla, medially 128). Whether this groove represents a nat- with the frontals, but has no contact with the ural condition or an artifact cannot be deter- nasals. Posteroventral to the maxillary-pre- mined with the available sample. The fron- frontal contact, the lacrimal is well devel- toparietal suture shows a slight undulation, oped and forms about the anterior one third rather than being a simply straight suture. of the ventral border of the orbit. Having no The parietal table is trapezoidal in shape, posteroventral process, the jugal is shaped having its maximum width at the anterior like a hockey stick: it has a short ``blade'' border, a slightly constricted waist and a nar- that forms the ventral rim of the orbit to- row posterior width. The lateral border of the gether with the lacrimal and a slender and table is ¯anged for the lateral origin of the long ``handle.'' The posterodorsal process of temporal muscles, and the posterior border is the bone has a pointed end that is not ex- also ¯anged with a poorly de®ned median tended to contact the squamosal (®g. 17A± ridge. In dorsal view, the anterior part of the C). table is ornamented with osteodermal rugos- The postfrontal is slender, and is clearly ities, but the posterior part of the table is sutured to the postorbital laterally. Having smooth (®g. 17C). The parietal foramen is slender and elongate anterior and posterior relatively large in proportion to the table, and processes, the postfrontal is deeply forked it opens anteriorly close to the frontoparietal medially to clasp the frontoparietal suture. suture. The supratemporal process is slender The postorbital has a triangular base and an and long, having a well-de®ned dorsal crest. extremely slender and long posterior process, The process posterolaterally contacts the su- which ®ts in the medial groove of the squa- pratemporal bone, posteroventrally contacts mosal and forms the anterior part of the su- the paroccipital process of the occiput, and pratemporal arch. The anterior border of the has no contact with the quadrate. postorbital forms the posterior rim of the or- The maxillae are well preserved on both bit, together with the postfrontal. Its postero- sides of the specimen. Each element carries lateral border, however, has an articular sur- 15 teeth to form a complete tooth row (see face for the posterodorsal process of the ju- below). In lateral view, the maxilla is elon- gal. gate and roughly triangular, having a low na- The squamosal is greatly reduced in thick- sal process with its apex at the midlevel of ness, with a thin and very lightly built base. the tooth row (®g. 17A, B). The lateral sur- It bears a well-de®ned dorsal process hooked face of the element is smooth with no osteo- anteriorly, and a notched anterior border dermal ornamentation and is penetrated by forming the posterior rim of the supratem- six lateral superior alveolar foramina (or poral fenestra (®g. 17C). The squamosal maxillary foramina) along the ventral border lacks a lateral process, but the anterior pro- of the bone. The ®rst alveolar foramen is sig- cess is slender and elongate, and is medially ni®cantly larger than the others on the same grooved for the posterior process of the post- specimen. Anteriorly, the premaxillary pro- orbital. The supratemporal bone is quite well cess overlaps the premaxilla without devel- developed. It attaches to the lateral side of opment of any kind of foramen or aperture the supratemporal process of the parietal, as at the suture. The anterior palatal process is normally seen in other lizards; but it extends a well-developed medial extension, but has more posteriorly than the latter process to no midline contact with its opposite element. contact the cephalic condyle of the quadrate. This process has a concave dorsal surface, Therefore, the supratemporal is involved in forming the ¯oor of the narial opening. The quadrate suspension together with the squa- posterior wall of the narial opening is pene- mosal. trated by a single foramen, representing the The quadrate is completely preserved on 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 59 both sides, and is in articulation with the notch of the pterygoid. Because of the vo- skull and mandibles. The element is slender- mer-pterygoid contact, the palatine does not ly built and relatively straight, lacking the form the border of the interpterygoid vacuity strong arching seen in some other lizards. (pyriform recess), and the vacuity is extreme- The anterior surface of the quadrate has a ly narrow as a consequence of the width of low ridge, running from the cephalic condyle the palatal elements. toward the ventral condyle. This vertical The pterygoid is not a simple Y-shaped el- ridge separates the narrow tympanic crest ement, differing from most of other scinco- from the much wider medial conch, and may morphs except some macrocephalosaurs and served as the origin of the 3a portion of the some lacertiforms. Besides the palatal and MAME muscles (Oelrich, 1956; Rieppel, ectopterygoid processes normally seen in 1980c). Medial to the vertical ridge, the other lizards, it has a well-developed antero- quadrate is strongly widened, concave, and lateral process that forms part of the medial is much posterior in relation to the tympanic rim of the suborbital fenestra. The antero- crest. The medial border of the quadrate is medial (palatal) process is long and anteri- straight, lacking a pterygoid lappet. The dis- orly abuts the vomer. The lateral (ectoptery- tal condyle is typically saddle-shaped with a goid) process is very short, as commonly shallow ventral notch. Above the notch is a seen in other lizards, contacting the ectopter- small pocketlike depression, in which opens ygoid and forming the posterior rim of the three small foramina for the anastomotic suborbital fenestra. Although not completely branch of the anterior tympanic vein and pos- exposed on the specimen, the posterior terior condylar artery (Oelrich, 1956). A sin- (quadrate) process medially has an articular gle quadrate foramen is the common condi- fossa at the base for the basipterygoid pro- tion in most lizards, and the presence of three cess. Remnant pterygoid teeth are developed foramina in a small pocket may well be a in the middle part of the element and extend unique condition for Gobinatus. close to the border of the interpterygoid va- PALATAL ELEMENTS: Preparation of the cuity. skull revealed a well preserved palate (®g. The ectopterygoid is weakly developed, 17D). The vomer (left side shown on the and it lacks a robust ventral process as seen specimen) is wide and strongly elongate, in some other macrocephalosaurs (e.g., with its posterior extension approaching the Adamisaurus). However, it has a slender an- level of the posterior end of the maxillary terior process contacting the palatine, and tooth row (see discussion below). Concealed consequently excluding the maxilla from en- by the right dentary, the right side of the vo- tering the suborbital fenestra. The fenestra it- mer cannot be exposed for observation, but self is greatly reduced to a narrow slit, in it must have a midline suture contact with keeping with the widening of the palatine the left vomer as indicated by the width of and the pterygoid. the left element. Most of the element is an BRAINCASE: The braincase ¯oor is well ex- elongate thin plate with a well-de®ned pos- posed in ventral view on IGM 3/126. Unfor- teromedial process that extends between the tunately the lateral wall and occipital aspect palatines and contacts the anterior process of of the braincase cannot be observed as pre- the pterygoid. The ventral surface of the vo- served. The braincase ¯oor is marked with mer is slightly convex and smooth, lacking three distinct depressions (or pits): a single any trace of vomerine teeth. anterior one in the middle part of the basi- The palatine is also wide and toothless. sphenoid and a pair posteriorly on the basi- Anteriorly it has an extensive sutural contact occipital (®g. 17D). Functionally, the devel- with the vomer, and a spikelike lateral pro- opment of these depressions probably in- cess for articulation with the posterior palatal creases attachment surfaces for the ventral process of the maxilla. Posteriorly, the pala- axial musculature (Oelrich, 1956). The bas- tine has a triangular extension, the medial ipterygoid process is wide and platelike. An- border of which overlaps the lateral border teromedially, the parasphenoid process has a of the anteromedial process of the pterygoid. slightly widened base, but lacks a well-ossi- The tip of this process ®ts in a V-shaped ®ed rostrum. The basisphenoid/basioccipital 60 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249 suture is medially irregular and laterally di- and the splenial. The medial process is pen- agonal. The basisphenoid symmetrically has etrated by a small posterior mylohyoid fo- on each side a very slender process extend- ramen below the posteroventral process of ing posteriorly to form the anterior part of the coronoid. The posterior part of the an- the spheno-occipital tubercle. The tubercle it- gular widens slightly and turns dorsolateral- self is slender but prominent, and is more ly, terminating at the same level, and im- ventrally than laterally directed. The occipital mediately below, the posterior surangular fo- condyle is well exposed on the specimen. ramen (®g. 17B). The posterior end of the The basioccipital forms most of the condyle, angular is slightly notched (shown by clear with the exoccipitals laterally each contrib- impressions), differing from the strongly bi- uting slightly less than one third of the con- furcated condition seen in Tchingisaurus dyle. multivagus (see below). A much stronger ex- MANDIBLE: The mandible is well preserved tension is seen in Adamisaurus magnidenta- on both sides, with only the ventral border tus, in which the angular terminates at the slightly damaged on the left mandible. The level of the craniomandibular joint (see lateral surface of the dentary is smooth, and above). is penetrated by seven mental foramina. The The articular and prearticular are entirely anterior four foramina are close to one an- fused as in many other lizards. The retroar- other, but the posterior three are irregularly ticular process has a wide base at the level spaced and are far apart from one another. of the articular fossa of the jaw, but narrows The last foramen opens at the midlevel of the posteriorly and ends with a slender tubercle tooth row. The posterior border of the den- that is strictly posteriorly directed. tary is clearly notched for the surangular and In medial view, the subdental shelf is sig- a small part of the angular bone. Both the ni®cantly reduced to a very slender structure, posterodorsal and the posteroventral process- and the sulcus dentalis medial to the shelf is es are slender and short, terminating roughly entirely lost. The splenial is slender and elon- at the same level below the coronoid summit. gate. It anteriorly extends to a point close to The surangular bone occupies most of the the mandibular symphysis and posteriorly lateral surface of the postdentary part of the terminates at the level of the posterior my- jaw. The ventral border of the surangular lohyoid foramen, where it may contact the bone forms a prominent ridge (adductor posteroventral process of the coronoid bone. crest) for attachment of the external mandib- The anterior inferior alveolar foramen is sig- ular adductor muscles. This crest extends ni®cantly enlarged and located below the along the surangular-angular suture, curving fourth tooth position from the back (®g. up posteriorly to the posterior surangular fo- 17A). The anterior mylohyoid foramen is ramen anterolateral to the craniomandibular much smaller and is very close to, and right joint. The anterior surangular foramen is rel- below, the former foramen. atively large and is located posterior to the DENTITION: As mentioned above, the pre- dentary-surangular suture, below the coro- maxillae bear seven teeth counting from the noid apex. Most of the lateral surface of the broken bases. The maxillary and dentary bone is smooth, but the ventral adductor crest teeth are well preserved. These teeth are is slightly ornamented with scarlike sculpture characteristically thick and bulbous, and the for attachment of the adductor muscles. crowns are unicuspid and posteromedially The angular bone is incompletely pre- curved. The tooth implantation is subpleu- served on both sides, but clear impressions rodont, having about one third of the teeth allow con®dent interpretation of the shape attached to the low lateral parapet of the and extent of this element. Anteriorly in ven- jaws. The complete maxillary tooth row con- tral view, the angular is narrowly wedged by tains 15 positions as shown on both sides of the slender posteroventral process of the den- the upper jaws. The ®rst ®ve teeth are similar tary, so that it is bifurcated as exposed: a in size and are more strongly recurved than small lateral process intervenes between the other teeth; the sixth tooth is signi®cantly surangular and the dentary, and a similar pro- smaller than others, creating a ``step'' in the cess medially intervenes between the dentary tooth row. Those in the middle and posterior 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 61 part of the tooth row have their crowns more rodlike than bladelike. The anterior border of inwardly curved than posteriorly, but the last the scapula is largely covered by the clavicle, four teeth are slightly smaller than those in but two barlike structures exposed represent front of them. the mesoscapular process and the procora- The complete dentary tooth row contains coid process, respectively (®g. 18). The 18 positions. The lower dentition shows a rounded coracoid foramen is located between similar pattern to the upper dentition, but in- the glenoid fossa and the notched border of crease in tooth size from the middle to the the anterior coracoid emargination. No pos- posterior part of the tooth row is more pro- terior coracoid emargination is developed. nounced. Despite the thickened tooth shafts, The right humerus is completely preserved both the maxillary and dentary tooth rows and is exposed in ventral view. It has a slen- have teeth that are widely spaced from one der shaft with expanded proximal and distal another. No teeth show development of re- ends capped by ossi®ed epiphyses. Proxi- placement pits, and this may re¯ect suppres- mally, it has an anterior crest for the attach- sion of tooth replacement in adult individuals ment of M. subcoracoscapularis, and poster- (MacLean, 1974). oventral to the crest is a triangular depression POSTCRANIAL SKELETON: A partial postcra- for M. coracobrachialis brevis (Romer, nial skeleton of the same individual is pre- 1956). The distal end of the bone is slightly served in association with the cranial mate- wider than the proximal end. The entepicon- rial. Exposed in ventral view, the preserved dyle is more robustly developed than the ec- part of the skeleton includes eight articulated tepicondyle, but neither an entepicondylar vertebrae, the right clavicle in articulation nor an ectepicondylar foramen can be iden- with the scapula-coracoid complex, and the ti®ed on this specimen. Between the con- right humerus in articulation with the pec- dyles are the capitellum (or radial condyle) toral girdle (®g. 18). The interclavicle is not and the trochlea (or ulnar condyle) as seen preserved. in other lizards. Differing from the common The eight vertebrae include the posterior condition seen in most lizards, however, a four or ®ve cervicals, as these bear short and well-de®ned triangular fossa is developed expanded that could not have connected above the two condyles, and a foramen opens with the sternum. In articulation with these in the fossa. A similar condition is seen in cervicals are the ®rst three or four anterior extant teguixin (AMNH dorsal vertebrae. All these vertebrae have a 141941), but the actual nature of this simi- procoelous centrum, which is triangular in larity needs further investigation. ventral view. As the vertebrae are exposed in ventral view, the morphology of the neural arch cannot be examined. The centrum of all COMPARISON AND DISCUSSION these vertebrae is ventrally crested, but the sharpness of the crest is reduced posteriorly. In tooth morphology and jaw structures, The intercentra remain separate from the cen- all three referred specimens clearly show di- trum and are in an intervertebral position. agnostic features of Gobinatus arenosus; ac- The clavicle is slightly shifted laterally, cordingly, they are referred to this particular and so is in articulation with the anterior bor- species. One specimen (IGM 3/126) repre- der of the scapula blade. The element is an- sents the best-preserved material known for gulated, but has no clavicle fenestra. The this lizard, allowing us to revise the diag- proximal end is a narrow, slender rod. The nosis of the species (see above). Alifanov's main part of the clavicle is a wide blade with (1993b) diagnosis included two other fea- a sharp edge that dorsally becomes slender tures: trigeminal notch anteriorly closed, and and extends to the dorsal end of the scapula pterygoid strongly bent to the level below the to presumably contact the suprascapula (an maxillary tooth row; however, the type spec- unossi®ed element not preserved). imen (PIN No. 3142/308) as ®gured appears The scapula and the coracoid plate are to show that both the braincase and the pter- completely fused, as no suture can be delim- ygoid have been distorted (see Alifanov, ited. The scapula is thick and narrow, more 1993b: ®g. 3c). Therefore, the two features 62 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249 in question are more likely to be artifacts both have bulbous teeth with unicuspid than to be diagnostic of the species. crowns. The structural differences recog- The tooth number of this species is indi- nized by comparison of the ®gures are that vidually variable. The holotype was de- Dzhadochtosaurus giganteus has substantial- scribed as having 20 maxillary and 24 den- ly longer nasals and lacks a posterior notch tary teeth (Alifanov, 1993b), while IGM 3/ of the angular. A slender spikelike premax- 126 and 3/128 both have 15 maxillary teeth, illary spine is ®gured for the holotype of the and the former specimen has 18 dentary species; however, this morphology is highly teeth. Therefore, the variation range is about doubtful as the same specimen (PIN No. ®ve or six positions. 3143/103) is ®gured as having a complete The relationships of this scincomorph liz- premaxilla in dorsal view, but in lateral view ard are uncertain, although it was classi®ed it is ®gured as missing most of this element in the Mongolochamopinae (Macrocephalo- (Alifanov, 1993b: ®g. 2). sauridae) by Alifanov (1993b). In light of Nonetheless, Gobinatus arenosus and this uncertainty, it is worthwhile to discuss a Dzhadochtosaurus giganteus are probably few features that may bear on the relation- more closely related to one another than to ships of this lizard. any other scincomorphs, as indicated by their (1) The vomer is strongly elongate, with astonishing similarities in skull con®gura- its posterior extension approaching the level tion, jaw structure, and tooth morphology. of the posterior end of the tooth row. Such a condition of vomer elongation is similar to that in many advanced anguimorphs (see Tchingisaurus multivagus Alifanov, 1993 Rieppel, 1980a). However, in Adamisaurus Figure 19 the vomer is also extremely wide, as is typ- HOLOTYPE: PIN No. 3142/309, nearly ical of other scincomorphs. Anguimorphs complete left mandible with well-preserved have an extremely narrow vomer associated teeth. with the elongation of the fenestra exochoan- YPE LOCALITY AND HORIZON: Khermeen alis (Rieppel, 1980a). T (2) As shown on both the holotype (Ali- Tsav, Nemegt Basin, Mongolia; Upper Cre- fanov, 1993b) and the new specimens, the taceous Barun Goyot Formation. posterior end of the angular bone in Gobi- KNOWN DISTRIBUTION: Barun Goyot For- natus is slightly notched. The notch condi- mationÐKhermeen Tsav (Alifanov, 1993b); tion differs from the deeply bifurcated con- Djadokhta FormationÐUkhaa Tolgod (this dition in Tchingisaurus multivagus (see be- paper). low), and the angular extends to the posterior REVISED DIAGNOSIS: Polyglyphanodontine surangular foramen. Pending the evaluation differing from other members of the group of this character (i.e., possible ), in having the following derived character the condition in Gobinatus arenosus may states: Parietal foramen greatly reduced to a represent a more plesiomorphic state than minute opening on parietal table; marginal that in Tchingisaurus multivagus. Our obser- teeth have cylindrical basal part of shaft with vation of a new specimen of Pyramicephal- abruptly expanded and bulbous crowns; osaurus cherminicus (see below) indicates cusp-bearing part of crowns laterally com- that the latter species may also share this pressed and symmetrically tricuspid with condition with Gobinatus arenosus. higher central cusp and equally developed (3) In spite of their signi®cant difference lateral accessory cuspules; angular bone en- in size (30 mm vs. 50 mm), Gobinatus ar- larged and posteriorly bifurcated; prominent enosus and Dzhadochtosaurus giganteus as adductor crest present on lateral surface of ®gured (compare Alifanov, 1993b: ®gs. 2, 3) surangular; retroarticular process straight, are astonishingly similar to one another in slender, and pointed. general con®guration and several speci®c REFERRED SPECIMEN: IGM 3/129 (MAE features. They both have slender processes of 95-92), incomplete skull articulated with the forked postfrontal, both have the subor- mandibles from Ukhaa Tolgod (Camel bital fenestra reduced to a narrow slit, and Humps sublocality). 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 63

Fig. 19. Tchingisaurus multivagus: A±C, IGM 3/129, incomplete skull with mandibles, dorsal, left and right lateral views.

DESCRIPTION fore, it is described in detail. Although fairly complete, the specimen is preserved with an This species is previously known from a open-jaw position, and this makes it dif®cult single mandible only. IGM 3/129 is the ®rst to expose the palatal region without removal skull material known for this species; there- of the lower jaws. 64 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249

SKULL ROOF: The skull has a pointed snout the premaxilla, nearly contacting the oppo- with a laterally bulging cheek region, giving site element. No aperture is developed at the it a subtriangular shape anteriorly (®g. 19A). premaxillary-maxillary suture. The posterior The orbit is large and subcircular comprising process of the maxilla is a short triangle. a large part of the facial region of the skull. Along the dorsal margin of the process are The premaxillae are fused, and bear seven the well-developed lacrimal and anteroven- teeth. The anterior surface of this element is tral processes of the jugal, which together smooth, without premaxillary foramina. The form the ventral border of the large orbit. spine is broken and largely missing; hence, Like in Gobinatus arenosus (see above), the the length and shape of the spine cannot be jugal has an extremely slender posterodorsal determined. The nasals are not preserved, but process and lacks a posteroventral process, impressions indicate that they were paired but the jugal of this species is more angulat- and would laterally contact the dorsal pro- ed than in the former species. The dorsal pro- cess of the maxilla. cess of the jugal contacts the postorbital The frontals are paired and slightly con- along a short suture. It can not be determined stricted between the orbits. These elements whether the jugal contacted the squamosal, are anteriorly broken and their suture pattern because of the incomplete preservation of the with the nasals, and possibly with the max- latter element on the specimen. illa, cannot be identi®ed; however, they lat- The prefrontal is well developed, forming erally have an extensive sutural contact with the anterior rim of the orbit. It is laterally the prefrontal. The dorsal surfaces of the articulated with the maxilla, medially with bones are lightly ornamented with osteoder- the frontal, but is possibly separated from the mal rugosities. The posterior borders of the nasal by the anterolateral process of the fron- frontals each have a shelf underlying the an- tal (not preserved). The frontal process of the terior border of the parietal. prefrontal is very short, terminating far an- The parietal is short and trapezoidal. Its terior to the midlevel of the orbit. The post- anterior border slightly overlaps the frontals frontal and the postorbital are clearly sepa- and has an irregular wavy suture with the rate elements, and the two together form a frontals. The parietal foramen is greatly re- short bar separating the orbit from the supra- duced as a small, round opening located temporal fenestra. The postfrontal is medi- close to the center of the parietal table. The ally well forked to clasp the frontoparietal lateral ¯ange of the table is deep and nearly suture, and is laterally notched to receive a vertical, indicating a lateral origin of the tem- small triangular wedge of the postorbital. poral muscles. The table sharply narrows The latter element has a very short anterior posteriorly, and the posterior ¯ange of the process (shown on the left side), but the pos- table is more sloped than the lateral ¯ange terior process (preserved on the right side) is (®g. 19A). The supratemporal process of the slender and long. parietal is slender, and is much longer than Only the right squamosal is partially pre- the parietal table. The articulation pattern of served. It is slightly dislocated vertically and the supratemporal process with the quadrate is closely associated with another small splint is unknown, owing to the lateral dislocation bone, which is probably the supratemporal. of the quadrate on both sides of the skull. The base of the squamosal is widened slight- The maxilla is incompletely preserved on ly, and has a weakly developed dorsal pro- both sides (®g. 19B, C). The dorsal process cess. The anterior process of the squamosal is high, rising above the anterior two thirds is slender and is medially grooved for recep- of the tooth row. The lateral surface of the tion of the posterior process of the postor- process is smooth, slightly concave, and is bital. ventrally penetrated by a row of small lateral The quadrate is well preserved on both superior alveolar foramina. The premaxillary sides. The element lacks an anterior arching, process is a very short spike, attached to the with a straightly vertical tympanic crest (ex- lateral surface of the premaxillae. The an- cept for the lateral edge of the cephalic con- teromedial process is so strongly developed dyle). Anteriorly, the quadrate has an ex- that it extends medially behind the base of tremely narrow and convex lateral part, but 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 65 a much wider and strongly concave medial and are caniniform with pointed, unicuspid extension. The medial crest is oblique, run- crowns. The other 15 teeth are conspicuously ning from the medial side of the cephalic bulbous and tricuspid; however, the base of condyle to the distal condyle. The crest lacks the crown is very narrow (see ®g. 19B, C). a pterygoid lappet of the quadrate. The distal The central cusp is well developed, and far condyle is ventrally notched, with a well-de- more prominent than the lateral accessory ®ned lateral epicondyle. Above the notch, a cuspules. The lateral cusps are actually not single quadrate foramen is present on the an- well de®ned, instead, they are miniature hor- terior surface as seen in most of other lizards izontal crests that are not well separated from generally. the main cusp. This crown pattern is different MANDIBLE: The mandible is robust, having from that in Pyramicephalosaurus chermin- a strongly convex lateral surface. The pos- icus (see below), in which the three cusps are terior border of the dentary is deeply notched similar in height and the lateral cusps are to a level slightly anterior to the posterior clearly separated from the main cusp by a end of the dentary tooth row (contra Alifan- well-developed groove. ov, 1993b: ®g. 7). The coronoid process of The dentary tooth row is incompletely pre- the dentary does not extend onto the anterior served on both sides, because the anterior tip surface of the coronoid, but on its ventral of both jaws is missing. The left side has 14 edge it fully articulates to the surangular teeth and the right side has 16 teeth pre- bone, leaving no space for the coronoid to served. The total number of dentary teeth can wedge in. The dentary-surangular suture in be estimated as about 19±20 on comparison this specimen ends dorsally at the anterov- with the upper dentition. This estimation is entral tip of the coronoid dorsal process, very close to the holotype mandible (PIN rather than at the midlevel of the latter pro- No. 3142/309), which is illustrated as having cess as ®gured for the holotype (Alifanov, 19 teeth (but described as having 17, see Al- 1993b: ®g. 7). The posteroventral process of ifanov, 1993b). All the marginal teeth are the dentary has a similar extension, and ter- subpleurodont, with slightly less than half of minates at the same level as the posterodorsal the tooth attached to the lateral parapet of the process. tooth row. This description is different from Anteriorly, the surangular has a blunt pro- the ®gure of the holotype mandible (Alifan- cess that ®ts into a notch of the dentary. The ov, 1993b: ®g. 7), in which the dentary teeth anterior surangular foramen is small and are ®gured as acrodont (see comments be- close to the surangular-dentary suture, below low). the anterior tip of the coronoid summit. The posterior surangular foramen is even smaller, COMPARISON AND DISCUSSION and is located posterodorsally, close to the glenoid fossa of the jaw. Running between Alifanov (1993b) named Tchingisaurus the two foramina is a ventrally curved ad- multivagus on the basis of a single left man- ductor ridge on the lateral surface of the sur- dible (PIN No. 3142/309) from Khermeen angular. Ventral to this ridge, the angular Tsav (Barun Goyot Formation), and referred bone is proportionally wide and has exten- the species to the Macrocephalosauridae Su- sive exposure on both the medial and lateral limski, 1975. Because the family Macroce- side of the jaw. As in the holotype specimen, phalosauridae is inadequately diagnosed and the angular is posteriorly bifurcated and ter- the monophyly of the group is highly ques- minates anterior to the posterior surangular tionable (Estes, 1983), the referral of Tchin- foramen. gisaurus multivagus to the family is prob- DENTITION: The premaxillae are fused into lematic. We tentatively classify the taxon in a single bone with seven teeth. The crown the Teiidae, pending wholesale revision of pattern of the premaxillary teeth cannot be this and allied taxa. observed because of erosion. The complete The new specimen from Ukhaa Tolgod is maxillary tooth row contains 18 teeth (shown identical to the holotype of Tchingisaurus on both sides of the specimen). The ®rst multivagus in jaw con®guration, crown pat- three maxillary teeth are larger than the rest, tern of the marginal teeth, and in having an 66 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249 angular that is posteriorly bifurcated. On the men from Khulsan has 16 dentary teeth, see basis of these similarities, the new specimen below). is referred to this species. The deceptive dif- As alluded to above, the new specimen ferences in number and implantation of the from Ukhaa Tolgod has subpleurodont teeth, teeth in the two specimens (see above) are differing from the ``acrodont'' condition of probably the result of a descriptive or illus- the holotype mandible ®gured by Alifanov tration error in the original description of the (1993b: ®g. 7). This supposed difference is holotype specimen. Alifanov (1993b: 89) de- probably not individual variation, but is like- scribed the teeth on the holotype as ``high ly to be observational. The holotype speci- above level of upper margin of subdental men is unavailable for this study, and the un- crest,'' but ®gured them as acrodont (Alifan- certainty about its tooth implantation cannot ov, 1993b: ®g. 7). be clari®ed until the specimen is reexamined. In terms of tooth morphology, the closest similarity of Tchingisaurus multivagus is to Pyramicephalosaurus cherminicus Alifanov, Pyramicephalosaurus cherminicus Alifanov, 1988 1988. The two forms share similarities in [nom. correct. Alifanov, 1993b having bulbous teeth with strongly constrict- (pro Piramicephalosaurus cherminicus ed crown bases, but are clearly different from Alifanov, 1988)] one another in detailed crown pattern and the Figure 20 mode of tooth implantation as described above (see also description of P. cherminicus HOLOTYPE: PIN No. 3142/307, incomplete below). In addition, these two species (to- skull with mandibles. gether with Gobinatus) differ from the so- TYPE LOCALITY AND HORIZON: Khermeen called macrocephalosaurs in lacking a prear- Tsav, Nemegt Basin, Mongolian Gobi Des- ticular crest medially at the base of the ret- ert; Upper Cretaceous Barun Goyot Forma- roarticular process. Such a crest (which dif- tion. fers from the ®ngerlike process in iguanians) KNOWN DISTRIBUTION: Khermeen Tsav and occurs in most lacertids, xantusiids, and tei- Khulsan, Nemegt Basin, Mongolian Gobi ids (see Estes et al., 1988: character 73). Desert; Upper Cretaceous Barun Goyot For- Functionally, the crest is for attachment of mation. the pterygoideus muscle (Rieppel, 1980c), REVISED DIAGNOSIS: Scincomorph lizard and lack of such a crest in Tchingisaurus distinguished from other members of the multivagus may indicate a fundamental dif- group by the following derived character ference in muscle attachment from the ma- states: skull lightly built, with pointed snout; crocephalosaurs. parietal table rectangular, having relatively If Alifanov's (1993b) observation is cor- straight lateral borders; well-ossi®ed para- rect, Pyramicephalosaurus cherminicus lacks sphenoid rostrum extending far anteriorly; a posterior bifurcation of the angular (but see marginal teeth laterally swollen but having below) that is characteristic of Tchingisaurus strongly constricted base of crown; cusp- multivagus. Other differences that Alifanov bearing part of crown laterally compressed (1993b) mentioned are either ambiguous or and conspicuously tricuspid; lateral accesso- invalid. For example, Tchingisaurus multi- ry cusps at same height but well separated vagus was described as differing from Pyr- from central cusp by well-de®ned groove; amicephalosaurus cherminicus in having a tooth attachment subacrodont, with extreme- ``larger number of teeth,'' but the holotype ly low parapet of tooth row less than one of the former taxon is ambiguously described third of tooth height. as having 17 teeth and ®gured as having 19. REFERRED SPECIMENS: IGM 3/130 (MAE Furthermore, the lower dentition of Pyrami- 91-30), incomplete skull with mandibles; cephalosaurus cherminicus on the holotype IGM 3/131 (MAE 70/244), incomplete right is incomplete (see Alifanov, 1988: ®g. 3); maxilla with well-preserved teeth; both spec- thus, the total number of lower teeth on the imens from Khulsan, Barun Goyot Forma- specimen is, in fact, unknown (a new speci- tion. 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 67

DESCRIPTION The newly recovered specimen IGM 3/130 is an incomplete skull with mandibles, which provides information on skull features of the species that are unknown from the holotype. As the specimen reveals supplementary in- formation for this poorly known species, a description based on this specimen is given below. SKULL ROOF: Although not preserved, the nasals were probably paired as in the holo- type (Alifanov, 1988: ®g. 3) as is suggested by the articular surfaces on the anterior part of the frontals. The frontals are paired, with a clear midline suture. The dorsal surface of the bone is smooth, without osteodermal or- namentation. Anterolaterally, the frontal con- tacts the prefrontal and the dorsal process of the maxilla, and hence, separates the prefron- tal from contact with the nasal. The posterior border of the frontals is incomplete, and the actual suture pattern with the parietal and the location of the parietal foramen cannot be de- termined. The parietal table is also incom- pletely preserved, but displays a roughly square outline with very short supratemporal processes. The premaxillae are not preserved, but are known (from the holotype) to be a single unit (Alifanov, 1988: ®g. 3). The maxillae are nearly complete on both sides. The dorsal process is located above the anterior part of the tooth row, and an elongated posterior process extends below the jugal. The lateral surface of the maxilla is smooth, but is pen- etrated by six irregularly spaced lateral su- perior alveolar foramina along the ventral border of the bone. Anteriorly, the premax- illary process is very short, and this process is separated from the anteromedial process by a small notch. The latter process is so well developed that it closely approaches and

← Fig. 20. Pyramicephalosaurus cherminicus: A, IGM 3/131, incomplete right maxilla with well-preserved teeth from Khulsan, lateral view; B, close-up shot showing crown pattern of IGM 3/130; C, D, IGM 3/130, incomplete skull with mandibles from Khulsan, dorsal and ventral views. Dislocated parietal is digitally placed back to its original position. 68 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249 nearly contacts its opposite element. At the developed anteriorly. Medial to this ridge, anterior surface of the nasal process of the each side has two vomerine apertures pene- maxilla, the anterior interior alveolar fora- trating the vomer. The anterior aperture is men is clearly identi®able. It opens slightly signi®cantly larger than the posterior one, above the level of the lateral superior alve- and the two are widely separated from one olar foramina. another. Posteriorly, the vomer has a trian- The medial aspect of the maxilla is best gular notch that receives the palatine. The shown on IGM 3/131. The supradental shelf vomer has a slender and ventrally ridged pos- is extremely thin but is well developed. The teromedial process, which separates the pal- dental gutter, however, is lost in keeping with atines along the midline but does not contact the development of subacrodonty. Anteriorly the pterygoid. above the shelf, and at the level of the third The palatines are very wide, reducing the and the fourth teeth, a small pocketlike struc- size of the anterior part of the pyriform re- ture is developed for articulation with the cess to a narrow slit. The lateral wing of the septomaxilla. The posterior interior alveolar element contacts both the maxilla and the ec- foramen is large, located above the sixth topterygoid (see below), forming the anterior tooth position from the rear. The supradental border of the suborbital fenestra. The pala- shelf posteriorly lacks a palatal process, in- tine forms the anterior half of the medial bor- stead, a scarlike surface dorsally on the shelf der of the suborbital fenestra, and it posteri- indicates the palatine-maxillary articulation. orly has a long triangular process wedging A short groove is developed posterodorsally into a small notch of the pterygoid. The con- on the shelf for articulation with the anter- cave ventral surface of the bone is smooth, oventral process of the jugal. without any trace of palatal teeth. The prefrontal is preserved on both sides. The pterygoid has a relatively short an- It has extensive sutural contact with both the teromedial process, which laterally articu- maxilla and the frontal, but is separated from lates with the palatine and medially forms the the nasal (not preserved) by the anterolateral border of the pyriform recess. There is a sig- process of the frontal. The lacrimal is well ni®cant gap between it and the posterior tip developed. It forms the anterior one third of of the vomer. At the base of the anteromedial the ventral border of the orbit. The jugal is process, remains of pterygoid teeth are clear- slender, and is only preserved on the right ly identi®able along the medial edge of the side of the specimen. The anteroventral pro- pterygoid. An even shorter anterolateral pro- cess of the jugal forms the posterior two cess forms the posterior half of the border of thirds of the ventral rim of the orbit. The the suborbital fenestra. The lateral process of base of the jugal is slightly expanded, but the pterygoid is short and robust, contacting lacks a clearly de®ned posteroventral pro- the ectopterygoid and forming part of the cess. The posterodorsal process is slender, posterior border of the suborbital fenestra. forming a complete bar at the back of the The posterior process is slightly shorter than orbit. the anterior process, but is laterally com- The postfrontal and postorbital are not pre- pressed as a blade. The medial surface of the served; neither are the squamosal and the su- process is only slightly concave. pratemporal. These elements are also un- The ectopterygoid is proportionally a known from the holotype, therefore, the mor- small element, with a very weakly developed phologies of the supratemporal fenestra and ventral process. However, a slender anterior upper temporal bar remain unknown for this extension forms the entire lateral border of species. the suborbital fenestra and excludes the max- PALATAL ELEMENTS: The palatal aspect is illa from the fenestra by contact with the vo- unknown on the holotype, but is well pre- mer. served on IGM 3/130 (®g. 20D). Anteriorly, BRAINCASE: The supraoccipital and exoc- the vomers are paired, having a straight su- cipital parts of the braincase are not pre- tural contact along the midline. The ventral served, but the ventral and partial lateral as- surface of the element shows no vomerine pects of the braincase were exposed with teeth, but a slanted, transverse ridge is well preparation for observation. The basisphe- 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 69 noid is proportionally large, forming more The mandibular fossa is wide open posterior than two thirds of the ¯oor of the braincase. to the ventral process of the coronoid. The It anteriorly has a well-ossi®ed cultriform retroarticular process is slender, straight and process, which is slender and extremely elon- directed posteriorly. It bears no medial crest gate, extending to the anterior end of the pyr- (prearticular crest) or angular process. iform recess and slightly bending dorsally. DENTITION: The marginal teeth of Pyram- The basipterygoid process is short and has a icephalosaurus cherminicus are closely sim- well-de®ned shaft and slightly expanded dis- ilar to those of Tchingisaurus multivagus in tal end articulating with the pterygoid. The being bulbous with a strong constriction at recessus vena jugularis is broken on both the base of the crowns. However, the teeth sides of the basisphenoid, and only part of of the two species are different in crown pat- the prootic is in articulation with the basi- terns and in the mode of attachment to the sphenoid. The basioccipital part of the brain- jaws. Differing from the blunt, low-cuspid case ¯oor is not preserved. crowns of Tchingisaurus multivagus, the MANDIBLE: The lower jaw is preserved on crowns of Pyramicephalosaurus cherminicus both sides of the specimen (IGM 3/130), are more sharply pointed, and the well-de- with little damage of the dentaries. The man- veloped lateral cuspules are clearly set off dible is very slenderly built, and is strongly from the central cusp by a vertical groove. laterally compressed. The lateral surface is Also, the cusp-bearing part of the crowns are smooth, and is penetrated by a row of small strongly laterally compressed and ¯ared. In mental foramina, the number of which can- terms of tooth attachment, the high-crowned not be determined owing to breakage of the marginal teeth of Pyramicephalosaurus cher- dentary. Posteriorly, the dentary has a well minicus have less than one third of the tooth de®ned coronoid process, which does not height attached to the extremely low lateral cover the lateral surface of the coronoid parapet of the tooth row. This type of tooth bone. The anterior surangular foramen opens attachment is best termed as subacrodont below this small process. The posteroventral (Gao and Fox, 1991, 1996). process of the dentary is broken on both On IGM 3/130, each maxilla has 13 teeth sides, and thus its extent cannot be deter- preserved, with probably the one or two an- mined on this specimen. teriormost missing in comparison with the The lateral exposure of the surangular is other known specimens. Both the holotype relatively narrow, as it is ventrally extensive- (Alifanov, 1988: ®g. 3) and IGM 3/131 have ly covered by the angular (shown as clear 15 teeth for the complete maxillary tooth impressions on both sides). The impressions row. The ®rst maxillary tooth is always slen- of the angular show that the element extends der and unicuspid, while the second tooth posterodorsally toward the posterior suran- could be the same as the ®rst (IGM 3/131) gular foramen, which opens anterior to the or weakly tricuspid (as ®gured for the holo- craniomandibular joint, as normally seen in type, see Alifanov, 1988: ®g. 3a). The third other forms. The posterior end of the angular and following teeth have strongly laterally is slightly notched, although it is not strongly compressed and ¯ared crowns, and the bifurcated as in Tchingisaurus multivagus. crowns are pointedly tricuspid. In medial view, the splenial is slender and The dentary tooth row on IGM 3/130 has elongate, closely approaching the mandibular 14 teeth exposed on the right side, and a total symphysis. The anterior inferior alveolar fo- of 16 for the complete tooth row on the left ramen is twice the size of, and directly side of the jaw. The ®rst tooth is slender and above, the anterior mylohyoid foramen; the conical, the second is slightly thicker with an two foramina are located at the level of the incipient anterior accessory cuspule. Like in posterior one third of the dentary tooth row. the upper dentition, the third through the six- The posterior extension of the splenial ter- teenth are strongly tricuspid. minates below the anteroventral process of the coronoid bone. Above the splenial, the COMPARISON AND DISCUSSION subdental shelf of the dentary is extremely The referral of the new specimens from slender and a sulcus dentalis is nearly lost. Khulsan to Pyramicephalosaurus chermini- 70 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249 cus is primarily based on the diagnostic tooth Macrocephalosaurus sp. form of the species (see diagnosis). The spe- Figure 21 cies is previously known from a single spec- SPECIMENS: IGM 3/132, partial skull and imen (holotype: PIN No. 3142/307) from postcranial skeleton; IGM 3/133 (MAE 51/ Khermeen Tsav, consisting of a partial skull, 93-25), disarticulated vertebrae. jaw material and vertebrae (Alifanov, 1988). LOCALITY AND HORIZON: Ukhaa Tolgod, The new specimen IGM 3/130 from Khulsan Nemegt Basin, Mongolian Gobi Desert; Up- provides more complete skull material for per Cretaceous Djadokhta Formation (Loope the species, and reveals some taxonomically et al., 1998). important features of this poorly known spe- REMARKS: IGM 3/132 consists of well-pre- cies. served premaxillae, maxillae, and partial From the skull roof elements, the frontals postcranial skeleton. The premaxillae are are paired and each side sends a slender an- fused, and carry ®ve pleurodont and unicus- terolateral process separating the nasal from pid teeth and vacant spaces for four others. the prefrontal as in most other scincomorphs. The maxillary teeth are typical of Macroce- In the palatal aspect, the ectopterygoid an- phalosaurus, being high-crowned, and hav- teriorly contacts the palatine excluding the ing a ¯ared and multicuspid crown pattern. maxilla from entering the suborbital fenestra. Although the teeth are similar to those of The latter feature, together with the devel- Macrocephalosaurus gilmorei, the specimen opment of subacrodonty, indicates a teiid re- cannot be con®dently identi®ed to species lationship of Pyramicephalosaurus chermin- without reference to other skull morphology. icus within the Scincomorpha. IGM 3/133 consists of several associated The angular bone is not preserved on IGM dorsal vertebrae. These are generally macro- 3/130, but clear impressions on both sides cephalosaur-type, as the vertebral centrum is indicate that the posterior end of the element strongly elongate and posteriorly narrowed. is slightly notched, posterodorsally approach- However, lack of cranial material makes it ing the posterior surangular foramen. This impossible to refer this material to any condition of the angular bone is different known species. from the ®gure of the holotype mandible, It is worth noting that IGM 3/132 and 3/ which shows a posteriorly nonbifurcated an- 133 are the only Macrocephalosaurus ma- gular bone (Alifanov, 1988: ®g. 3). Compar- terial out of over 1000 specimens that were ison with the holotype specimen is necessary collected from the Ukhaa Tolgod locality. As to clarify this morphology. this remarkably productive locality has been extensively sampled for several years, this Macrocephalosaurus Gilmore, 1943 ratio likely re¯ects the rarity of this particular herbivorous lizard in the Cretaceous verte- TYPE SPECIES: Macrocephalosaurus ferru- brate community at Ukhaa Tolgod. The pau- genous Gilmore, 1943. city of this and other herbivorous lizards at KNOWN DISTRIBUTION: Djadokhta and Ba- this locality may or may not re¯ect strati- run Goyot formations; Mongolian Gobi Des- graphic differences from the Khermeen Tsav ert. and Khulsan localities, as large herbivorous REVISED DIAGNOSIS: Differing from other species are also known from the classic Bayn closely related scincomorphs in having the Dzak locality (Djadokhta Formation). It is following derived character states: postorbit- likely that the rarity of large herbivorous liz- al elongate, reaching posterior border of su- ards at some localities indicates environmen- pratemporal region; supratemporal lost by fu- tal differences between these sites. sion with squamosal; parietal short, with pa- rietal foramen near or on frontoparietal su- Macrocephalosaurus chulsanensis ture; suborbital fenestra small or closed; Sulimski, 1975 angular process of lower jaw reduced to ob- Figure 22 tuse angle; teeth high-crowned and slender; HOLOTYPE: ZPAL MgR-I/14, nearly com- crowns ¯ared, laterally compressed, and mul- plete skull with mandibles and postcranial ticuspate. skeleton. 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 71

Fig. 21. Macrocephalosaurus sp.: IGM 3/132, A, fused premaxillae anterior view; B, left maxilla medial view; C, D, right maxilla, lateral and medial views.

TYPE LOCALITY AND HORIZON: Khulsan, morphology as the holotype of Macroce- Nemegt Basin, Mongolian Gobi Desert; Up- phalosaurus chulsanensis (®g. 22); also, it per Cretaceous Barun Goyot Formation. has the same pattern of osteodermal orna- KNOWN DISTRIBUTION: Khulsan and Mo- mentation. The parietal foramen is nearly nadnocks, Barun Goyot Formation. closed and is located at the frontoparietal su- DIAGNOSIS: ``Skull smaller (40-80 mm), ture (®g. 22A). On the basis of these simi- more delicate and slender, canine teeth less larities, the specimen is referred to Macro- well developed, tooth shafts projecting far- cephalosaurus chulsanensis. ther over parapet of jaw, skull sculpture more Among the three recognized Macroce- symmetrical (forming rosettes) and pectoral phalosaurus species, Macrocephalosaurus girdle more massive than in other species of chulsanensis is distinguished from Macro- Macrocephalosaurus; differs from M. gil- cephalosaurus gilmorei in having the parietal morei in having a more slender lower jaw; foramen opening at the frontoparietal suture, differs from M. ferrugenous in having lan- and having the suborbital fenestra entirely ceolate, polycuspate teeth'' (Estes, 1983: 83). closed. Other aspects of cranial and tooth REFERRED SPECIMEN: IGM 3/134 (MAE morphologies of the two species are aston- 215/92-47), incomplete skull with mandibles ishingly similar, and these two species are from Khulsan. not easily distinguished from the type species REMARKS: The specimen (IGM 3/134) Macrocephalosaurus ferrugenous, except for shows the same skull con®guration and tooth the signi®cant size differences (see Sulimski, 72 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249

lower dentition on the holotype specimen. (2) Anterior maxillary teeth are enlarged and caninelike, as clearly indicated by the signif- icantly thickened tooth bases. (3) Posterior teeth have widened and laterally compressed crowns, indicating multicuspid rather than bluntly chisellike crown pattern (see com- ments by Estes, 1983).

Erdenetesaurus robinsonae Sulimski, 1975 Figure 23A, B

HOLOTYPE: ZPAL MgR-III/19, incomplete skull with mandibles. TYPE LOCALITY AND HORIZON: Khermeen Tsav II, Nemegt Basin, Mongolian Gobi Desert; Upper Cretaceous Barun Goyot For- mation. KNOWN DISTRIBUTION: Only known from the type horizon. DIAGNOSIS: ``Skull high, well arched. Par- ieto-occipital region elongated. Maxilla mod- erately high, slightly inclined medially dor- sal. Postfrontal with poorly developed distal processes. Supratemporal fossa small, oval, slit shaped. Supratemporal bone squamous, vestigial. Parietal foramen in parietal. Pos- terior processes of the parietal diverge at an angle of about 80Њ. Frontals partially fused, posteriorly widened. Descending thickening of the parietal well developed. Ectopterygoid with a long anterior process. Lower jaw slen- der with slight posterior backward inclination of coronoid process. Retroarticular process wide and long. Dentition pleurodont, almost homodont. Tooth replacement of iguanid- type. Cheek tooth crowns rounded in outline, Fig. 22. Macrocephalosaurus chulsanensis: mediolaterally compressed with six-seven ra- IGM 3/134, A, B, incomplete skull articulated dially arranged denticles'' (from Sulimski, with mandibles from Khulsan, dorsal and lateral 1975: 78). views; C, close-up shot of right maxillary teeth. REFERRED SPECIMEN: IGM 3/135 (MAE 129/92-31), incomplete skull with mandibles 1975; Estes, 1983). The type species is based from Khermeen Tsav. on the holotype and only known specimen REMARKS: IGM 3/135 is a small specimen (AMNH 6520) from Bayn Dzak (Gilmore, (20 mm long), the size of which is only about 1943). Examination of the type specimen (K. half of the holotype of the species (ZPAL Gao, personal obs., 1998) permits clari®ca- MgR-III/19: 55 mm). However, it shows di- tion of the following points: (1) The marginal agnostic features of the species in tooth mor- teeth are pleurodont (contra Gilmore, 1943: phology and jaw structures: the teeth are acrodont; Estes, 1983: subpleurodont), as short crowned, having rounded crowns that they have at least half of the tooth height are aligned with no more than seven cusps; attached to the lateral parapet of the tooth the mandible is slender, lacking the typical row. The pleurodonty is best shown on the deepening and lateral swelling of the jaws in 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 73

Macrocephalosaurus species. On the basis of these features, the specimen IGM 3/135 is referred to Erdenetesaurus robinsonae. Sulimski (1975) noted the close similari- ties of Erdenetesaurus robinsonae with Cherminsaurus kozlowskii, and placed the two species in the Polyglyphanodontidae. The two species are similar in general con- ®guration of the skull, position of the parietal foramen, reduction of the suborbital fenestra, pattern of the postorbital-squamosal articu- lation, but are clearly different from one an- other in proportion of the parietal table and the orientation and cusp pattern of the crowns along the tooth row (see Sulimski, 1975). These two species may be closely re- lated to one another, but their relationships to Macrocephalosaurus, Adamisaurus, and Polyglyphanodon are far from clearly under- stood.

Cherminsaurus kozlowskii Sulimski, 1975 Figure 23C, D

HOLOTYPE: ZPAL MgR-III/24, skull with mandibles. TYPE LOCALITY AND HORIZON: Khermeen Tsav, Nemegt Basin, Mongolian Gobi Des- ert; Upper Cretaceous Barun Goyot Forma- tion. KNOWN DISTRIBUTION: Only known from the type locality and horizon. DIAGNOSIS: Polyglyphanodontine diag- nosed by the following characters: ``Skull length 65 mm; skull contours relatively un- modi®ed; snout region high, arched, but not widened; jaw robust but not deepened; den- tition essentially homodont, subpleurodont; tooth number low (19 dentary teeth); supra- temporal and squamosal separate; parietal fo- ramen in parietal; weak sagittal crest on pa- rietal; ectopterygoid with long anterior pro- cess; suborbital fenestra open; teeth large, crowns diagonally arranged at about 30Њ an- gle to axis of jaw; cutting edges of teeth with 5-6 low, blunt cusps; coronoid and dentary Fig. 23. Erdennetesaurus robinsonae: A, B, IGM 3/135, incomplete skull with mandibles from in contact'' (from Estes, 1983: 79). Khermeen Tsav, dorsal and lateral views; Cher- REFERRED SPECIMEN: IGM 3/136 (MAE minsaurus kozlowskii: C, D, IGM 3/136, left man- 256/92-23), incomplete skull with mandibles dible from Khermeen Tsav, lateral and medial and partial postcranial skeleton; IGM 3/137 views. (MAE 267/92-35), partial skull; both speci- mens from Khermeen Tsav locality, Barun Goyot Formation. 74 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249

Fig. 24. ?Scincoidea, family incertae sedis, Parmeosaurus scutatus, new genus and species: A, B, IGM 3/138 (holotype), skull with articulated postcranial skeleton from Ukhaa Tolgod, dorsal and ventral views.

REMARKS: As noticed by Sulimski (1975), well-preserved skull with articulated postcra- the most distinctive features of Cherminsau- nial skeleton. rus kozlowskii are the oblique arrangement of TYPE LOCALITY AND HORIZON: Ukhaa Tol- the marginal teeth along the tooth row and god, Mongolian Gobi Desert; Upper Creta- the chisellike crowns with ®ve to six low ceous Djadokhta Formation (Loope et al., cusps. The two specimens from Khermeen 1998). Tsav clearly show these diagnostic features KNOWN DISTRIBUTION: Known only from and they are accordingly referred to this spe- the type locality and horizon. cies. DIAGNOSIS: Sharing with scincoids the fol- Sulimski (1975) placed Cherminsaurus lowing derived character states: presence of kozlowskii together with Erdenetesaurus ro- both dorsal and ventral body osteoderms; ce- binsonae in the Polyglyphanodontidae. This phalic osteoderms present; palpebral ossi®- placement is accepted by Estes (1983) with cation present; lateral coronoid process of change of ranking of the familial group as a dentary large, extending dorsally onto an- subfamily (Polyglyphanodontinae). Howev- terolateral surface of coronoid; retroarticular er, the phylogenetic positions of the two taxa process in¯ected medially with small ¯ange in relation to other Gobi taxa (e.g., Macro- on medial margin. Differing from other scin- cephalosaurus, Adamisaurus) and Polygly- coids in having the following autapomor- phanodon need to be carefully investigated, phies: skull narrow and elongate, with later- before a reliable classi®cation scheme can be ally compressed snout; parietal table having provided. well-developed lateral ¯ange for dorsal ori- gin of temporal musculature; marginal teeth ?SCINCOIDEA OPPEL, 1811 stout with tricuspid crowns; autotomy frac- FAMILY INCERTAE SEDIS ture present behind caudal ribs. REFERRED SPECIMENS: IGM 3/139±3/142 Parmeosaurus scutatus, (MAE 475/93-152, 96-27, 95-70, 94-16), all new genus and species incomplete skull with mandibles; IGM 3/143 Figures 24, 25 (MAE 93-53), fragmentary cranial and post- ETYMOLOGY: parme (Gr.), small light cranial skeleton; IGM 3/144 (MAE 94-51), shield; scutatus (L.), armored with shield. articulated vertebrae with body osteoderms. HOLOTYPE: IGM 3/138 (MAE 95-30), All the referred specimens are topotypic. 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 75

Fig. 25. Skull of Parmeosaurus scutatus, new genus and species: A±C, IGM 3/139, incomplete skull with mandibles, dorsal, ventral, and right lateral views; D±F, IGM 3/140, incomplete skull with man- dibles, dorsal, ventral, and left lateral views. 76 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249

DESCRIPTION In lateral view, the maxilla is roughly a triangular bone with the apex of the dorsal SKULL ROOF: The skull of the holotype process located at the midlevel of the tooth specimen is concealed beneath the , and row. The dorsal process contacts the frontal, is exposed only in ventral view (®g. 24B). separating the nasal from the prefrontal. The However, several other specimens (IGM 3/ lateral surface of the maxilla is largely ver- 139±3/142) show that the dorsal aspect of tical and slightly concave, having six lateral the skull is covered with platelike osteo- superior alveolar foramina along the ventral derms. The skull is elongate and the snout is border. The posterior maxillary process is laterally compressed. Anteriorly, the premax- dorsally articulated with the well-developed illae are fused and have a slender dorsal lacrimal and jugal, and the latter two ele- spine that deeply intervenes the paired na- ments form the entire ventral border of the sals. The nasals have an anterior extension orbit. The jugal forms a complete postorbital lateral to the premaxillary spine, and poste- bar, although its dorsal process is much more riorly end with a thin plate that overlaps the slender than the anteroventral process. The frontal. element is generally hockey-stick shaped, The paired frontals anterolaterally contact having no trace of a posteroventral process the dorsal process of the maxilla, and this (®g. 25F). contact separates the prefrontal from the na- The prefrontal is dorsally covered by the sal. Posteriorly, the frontals are overlapped palpebral bones (IGM 3/139). When exposed by a squared off parietal tab, so that the fron- (IGM 3/140), it shows a well-de®ned frontal toparietal suture is not transverse (®g. 25A, process that extends to the midlevel of the D). The frontals have parallel lateral borders, orbit along the lateral border of the frontal. showing no interorbital constriction. Along The anteroventral process of the prefrontal the lateral borders is developed a palpebral forms the entire anterior wall of the orbit and series roo®ng the medial part of the orbit. ventrally contacts the palatine. This process The frontals have well-developed subolfac- laterally contacts the lacrimal and borders the tory ¯anges, but have no midline contact be- single lacrimal foramen. The process medi- low the olfactory tract. The descending pro- ally enters the orbitonasal fenestra, although cesses extend anteroventrally, but do not the well-developed descending process of the contact the palatines to prevent the prefrontal frontal forms part of border of the fenestra. from entering the orbitonasal fenestra. The postfrontal and postorbital are incom- The parietal table is penetrated by a small pletely preserved on IGM 3/140, and are dor- parietal foramen, which is located slightly sally covered with osteoderms. On IGM 3/ anterior to the center of the table. At the 142, however, the two elements are exposed frontoparietal suture, parietal tabs are present and seem to be separate as a suture can be as small triangular structures that are inter- identi®ed. The postfrontal is medially forked locked with the frontals. Laterally, the pari- to clasp the frontoparietal suture, and the etal has a well-developed ¯ange, the sloped postorbital has a long posterior extension surface of which indicates a dorsal origin of forming large part of the supratemporal arch. the temporal musculature. The ventral edge The supratemporal fenestra is normally de- of the ¯ange contacts the prootic bone (best veloped, although the squamosal is not pre- shown on IGM 3/140), but lacks a pointed served. downgrowth (ventral process of the parietal) PALATAL ELEMENTS: The vomers are in- that normally contacts the epipterygoid. The completely preserved on several specimens, supratemporal process of the parietal is elon- and are apparently fused with a prominent gate, and has an extensive lateral surface for midline ridge. The posterior vomer extension muscle attachment as the extension of the pa- reaches the level slightly posterior to the rietal ¯ange. The posterior end of the process midlevel of the tooth row, where the vomers reaches the paroccipital process, and appar- enter the interpterygoid vacuity between the ently has no contact with the quadrate. A palatines. The palatines are widened and small part of the right supratemporal bone is have a strongly concave ventral surface lat- preserved on IGM 3/140. eral to the vomers. A row of palatal teeth is 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 77 developed along the medial border of the much smaller opening (facial foramen) is bone. The posterior border of the palatine is more posterodorsally located in the trough. notched for articulation with the pterygoid. Laterally at the base of the spheno-occipital The pterygoid bears two rows of promi- tubercle, the occipital recess is small, nent teeth (best shown on IGM 3/140), which oblique, and narrowly elongate. It does not are closely packed along the medial border extend onto the lateral surface of the tuber- of the palatal process of the bone (®g. 25E). cle. The recess is separated by a small ridge The anterior process of the pterygoid forms from the more dorsally positioned foramen large part of the medial border of the inter- ovale, which is at about the same level as, pterygoid vacuity, and apparently has no but directly posterior to the facial foramen. contact with the vomer. Medially, a well-de- The lateral wall of the braincase is ob- ®ned ``mesopterygoid process'' functions to served on the left side on IGM 3/140, which enhance the articulation with the basiptery- also shows the best view of the braincase goid process of the basisphenoid. The lateral ¯oor as described above. As in other lizards, process of the pterygoid is thin but strongly the lateral wall of the braincase is mainly widened, with its posterior border forming a formed by the prootic. A well-de®ned alar weak crest for the attachment of the ptery- process projects anterodorsally contacting gomandibularis muscle. Posteriorly, the the ventral edge of the parietal ¯ange as pre- quadrate process is medially concave, form- served. Whether the process contacted the ing a shallow trough. epipterygoid cannot be determined, as the The ectopterygoid forms part of the pos- latter element is not preserved. Without dis- terior border of the suborbital fenestra and tortion, the well-developed anterior inferior has an interlocking articulation with the pter- process of the prootic is anteromedially di- ygoid. It has a robust anterolateral extension rected lying in a different vertical plane from to form the lateral border of the suborbital the alar process. Between the two processes, fenestra, but whether the extension contacted the trigeminal notch is narrow and deep, the palatine cannot be determined given the notching to the level of the anterior ampulla. condition of preservation of the specimens. MANDIBLE: The mandible is massive. The BRAINCASE: The braincase ¯oor is elon- posterior border of the dentary has a single gate, carrying a pit anteriorly and a knob surangular notch. Dorsal to the notch, the posteriorly, and in the middle of these two dentary displays a prominent coronoid pro- structure is a small foramen (best shown on cess extending onto the anterior surface of IGM 3/140; see ®g. 25E). The basisphenoid the coronoid. Ventral to the surangular is a and the basioccipital are completely fused, posteroventral process of the dentary that ex- and no suture can be delimited. Anterolater- tends roughly to the same level as the coro- ally, the basipterygoid process is short, and noid eminence. The surangular has a strong more anteriorly than laterally directed. Be- anterior process ®tting into the corresponding tween the basipterygoid processes, the ros- notch on the dentary. The anterior surangular trum is well ossi®ed and proportionally ro- foramen opens far posterior from the suran- bust. It extends anteriorly to the same level gular-dentary suture and slightly posterior to as the tip of the basipterygoid processes. The the coronoid eminence (IGM 3/139 shows braincase ¯oor is posterolaterally expanded, double openings, whereas the holotype and and the spheno-occipital tubercles project IGM 3/140 show only single openings). The ventrally. posterior surangular foramen is small and is Dorsolateral to the ¯oor, a troughlike re- in the typical position close to the jaw joint. cessus vena jugularis is deep with the well- The angular is a narrow band, covering the developed crista prootica forming the lateral surangular-prearticular suture and forming a wall. Within the recess, the posterior opening large part of the ventral border of the post- of the Vidian canal is located close to the dentary jaw. It has a slender anterior process middle of the trough, a short distance from that intervenes the surangular and postero- the base of the basipterygoid process. The ventral process of the dentary. canal opens at the suture between the fused In medial view, the well-developed splen- basisphenoid-basioccipital and the prootic. A ial extends anteriorly almost to the symphy- 78 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249 sis. The anterior inferior alveolar foramen the covering sheet of osteoderms, but some and the anterior mylohyoid foramen are lo- long bones can be observed in ventral view. cated posterior to the midlevel of the tooth The left forelimb has the radius exposed as row, and are located far apart. The posterior a slender element. The right hindlimb is well extension of the splenial terminates at the preserved, having the , tibia, and a level ventral to the dorsal summit of the cor- metatarsal preserved in articulation. The onoid. The prearticular and articular are hindlimb is quite robust, and the tibia is fused. The retroarticular process is broad, slightly shorter than the femur (®g. 24B). slightly in¯ected medially, and bears a small OSTEODERMS: One of the notable features tubercle (¯ange) on the medial margin (best of this lizard is the presence of osteoderms shown on IGM 3/139). The mandibular fossa covering both dorsal and ventral aspects of is elongate, opening between the posterior the skull and the body. The osteoderms on medial process of the coronoid and the cra- the skull roof are thin and platelike with es- niomandibular joint. The fossa is not ex- sentially no imbrication. Those covering the panded or in¯ated, a condition differing from ventral aspect of the skull are signi®cantly that seen in extant lacertiforms (Estes et al., smaller than those on the skull roof, and are 1988). more or less rhomboid and imbricated. DENTITION: The marginal teeth are fully The dorsal body osteoderms are rectan- pleurodont, having slightly over half of the gular. Having a well-developed gilding sur- tooth height attached to the lateral parapet of face anteriorly, these are imbricated one an- the tooth row. The premaxillae have as many other anteroposteriorly but are sutured later- as nine teeth, and these are unicuspid and are ally. The ventral osteoderms are also rect- about equal in size. The maxillary tooth row angular, but are even smaller than the dorsal contains 17±18 teeth, and the dentary con- ones. Each individual osteoderm is about half tains roughly 22 teeth. The ®rst four or ®ve the size of those covering the dorsal side of teeth on both maxilla and dentary are rela- the body; therefore, there are more ventral tively slender and unicuspid, those on the rows of osteoderms than dorsal ones. All the middle part of the tooth row have stout osteoderms have smooth surfaces and are not crowns and are bicuspid with a small anterior keeled. accessory cuspule. The most posterior teeth are short-crowned, very stout, and weakly COMPARISON AND DISCUSSION tricuspid. POSTCRANIAL SKELETON: The postcranial The referral of Parmeosaurus scutatus to skeleton is best preserved on the holotype. the Scincomorpha is supported by two char- The actual number of its presacral vertebrae acter states: nasal-prefrontal contact is lost, cannot be determined, but it appears to have owing to the presence of a frontal-maxillary had 26 or more (in keeping with the elon- contact; and the lateral process of the coro- gation of the body). The vertebrae are slight- noid is overlapped anteriorly by the dorsal ly elongate, with procoelous centra and low process of the dentary, so that the lateral ex- neural spines. The centra are procoelous. posure of the coronoid process is limited to Zygosphenes and zygantra are absent, and a narrow wedge between the dentary and sur- therefore, there are no accessory articulations angular (see Estes et al., 1988 for evaluation between vertebrae. The caudals are more of the characters). Presence of both dorsal strongly elongate than the presacrals and and ventral body osteoderms merits further have a longitudinal furrow on the ventral sur- investigation: it occurs in Scincidae and Cor- face of the centrum. At least the anterior cau- dylidae, as well as the Paramacellodidae dals have a single pair of caudal ribs fused (Evans and Chure, 1998). The rectangular to the centrum. The autotomy fracture is de- osteoderms in this Cretaceous lizard are sim- veloped right behind the caudal ribsÐa con- ilar to cordylids and paramacellodids, but dition known for some iguanians and gek- differ from the cycloid-type in most . kotans (Estes et al., 1988). This character was not investigated in either The pectoral and pelvic girdles on the ho- Estes et al. (1988) or Presch (1988) and po- lotype cannot be exposed without damaging larity is yet to be established. 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 79

Within the Scincomorpha, the new species ognize Clark's profound contribution in col- cannot be reliably classi®ed in a particular lecting vertebrate fossils, including many liz- subgroup because of con¯icting evidence. It ard specimens, from the Gobi Desert. shares with the Scincoidea (Scincidae ϩ Cor- HOLOTYPE: IGM 3/53 (MAE 154/93-40), dylidae) several derived character states. incomplete skull with mandibles. These include: cephalic osteoderms present; TYPE LOCALITY AND HORIZON: Ukhaa Tol- lateral coronoid process of dentary is large, god, Nemegt Basin, Mongolian Gobi Desert; extending dorsally onto anterolateral surface Upper Cretaceous Djadokhta Formation of coronoid; retroarticular process is in¯ected (Loope et al., 1998). medially; medial margin of the retroarticular DIAGNOSIS: Sharing with scincoids char- process has a tubercle or a small ¯ange; ret- acter states such as: retroarticular process in- roarticular process is broadened posteriorly ¯ected medially, broadened posteriorly; shar- (see Estes et al., 1988 for character evalua- ing with scincids presence of jugal-squamo- tion). In contrast, at least two character states sal contact. indicate a possible lacertiform relationship of Differing from other scincomorphs in hav- Parmeosaurus scutatus: presence of a pter- ing the following derived character states: ygoid lappet of the quadrate (best shown on presence of moderate retraction of narial IGM 3/139), and a facial region that is elon- openings; frontals proportionally wide; pres- gate with the snout laterally compressed (see ence of prefrontal-postfrontal contact; parie- Estes et al., 1988). Another character state, tal foramen greatly reduced as minute open- presence of palpebral ossi®cations, has been ing and located close to posterior border of interpreted as a separate synapomorphy for parietal table; occipital condyle formed ex- the Scincoidea, Lacertidae, and the Angui- clusively by basioccipital; posterior notch of morpha (see Estes et al., 1988), but it also dentary articulates with surangular only, occurs in the fossil group Paramacellodidae, without involvement of angular; retroarticu- which is probably the sister taxon of the lar process posteriorly notched; spheno-oc- Scincoidea (Evans and Chure, 1998). There- cipital tubercle greatly reduced, and shifted fore, this character state should be interpreted anteriorly close to midlevel of braincase as a synapomorphy for a more inclusive ¯oor. group. Alternatively, if the Paramacellodidae represent the basal clade of the Scincomor- DESCRIPTION pha (a hypothesis that needs to be tested), it would be a synapomorphy of Autarchoglossa The entire skull and the mandibles are with secondary loss within the Scincomor- generally well preserved without distortion. pha. However, the dorsal surface of the skull roof The available evidence seems to support was exposed in the ®eld and the elements referral of the new species to the Scincoidea, such as the nasals and the frontals are eroded but con¯icting evidence, such as having a and incomplete. pterygoid lappet on the quadrate and facial SKULL ROOF: The premaxillae are clearly elongation, signi®cantly weakens this refer- paired, with extremely slender and elongate ral. Pending wholesale revision of related dorsal spines. The nasals are incompletely taxa and the complete description and prep- preserved on both sides. Although the mid- aration of additional material, we tentatively line suture is not shown as preserved, there refer Parmeosaurus scutatus to the Scincoi- is no indication of fusion of the two bones. dea. The frontals are clearly separated by a midline suture and are proportionally wide Hymenosaurus clarki, with parallel lateral borders. Although lack- new genus and species ing a slender anterolateral process, the frontal Figure 26 contacts the dorsal process of the maxilla, so that the nasals are separated from the pre- ETYMOLOGY: hymen (Gr., god of marriage) frontals. The frontals have parallel lateral ϩ sauros (Gr., lizard), a present for Jim borders, lacking well-de®ned interorbital Clark's wedding; the species epithet is to rec- constriction. The lateral border is also ex- 80 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249

Fig. 26. Hymenosaurus clarki, new genus and species: A, B, IGM 3/53 (holotype), incomplete skull with mandibles from Ukhaa Tolgod, dorsal and ventral views. cluded from the medial rim of the orbit, be- contact the anterior process of the postfron- cause of the abutting contact of the prefrontal tal. This contact excludes the frontals from with the postfrontal. Ventrally, the subolfac- the medial rim of the orbit. The postfrontal tory ¯ange is fairly well developed, but is and postorbital are clearly separate elements. relatively shallow and has no contact along The postfrontal is proportionally larger than the midline. the postorbital, and is medially forked to The parietal table is roughly rectangular in clasp the frontoparietal suture. It has an elon- shape. It lacks lateral ¯anges, indicating a gate anterior process contacting the prefron- ventral origin of the temporal muscles; how- tal, and the two bones together form the me- ever, the posterior border of the table has a dial rim of the orbit and exclude the frontal well-developed ¯ange for attachment of the from entering the orbit. axial muscles. The parietal foramen is greatly The squamosal is preserved on both sides. reduced to a minute opening lying close to The element lacks a dorsal process, but the the posterior border of the parietal table (®g. 26A). Like in many extant skinks, the supra- anterior process is strongly elongated to have temporal process of the parietal distinctly an abutting contact with the jugal. The su- bends so the basal part of the process extends pratemporal is clearly identi®able on the laterally, then turns more posteriorly. Distal- right side of the specimen. It medially atta- ly, this process contacts the paroccipital pro- ches to the lateral surface of the paroccipital cess and is separated from the quadrate by process and the supratemporal process of the the supratemporal and the squamosal. parietal, and laterally contacts the squamosal The prefrontals have a slender and elon- and the cephalic head of the quadrate. The gate frontal process extending posteriorly to quadrate is strongly widened as commonly 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 81 seen in extant skinks and lacks a pterygoid is slender, but small denticles are identi®able lappet. on the ventral surface. The anterolateral pro- The maxilla is completely preserved on cess forms the entire posterior rim of the sub- both sides. The lateral surface of the bone is orbital fenestra, and contacts the ectoptery- smooth without osteodermal ornamentation. goid to form a very weak ventral process Above the ventral border is a shallow (pterygoid process). The ectopterygoid is groove, in which opens a horizontal row of small, and its short anterior process forms the lateral superior alveolar foramina. Anteriorly, posterior half of the lateral border of the sub- the premaxillary process is well developed in orbital fenestra. Thus, the maxilla contributes keeping with the narial retraction. It has a to the anterior half of the border of the sub- sutural articulation with the premaxilla, leav- orbital fenestra. ing no aperture between the two elements. BRAINCASE: The braincase ¯oor is well The anteromedial process is short, showing preserved, and is slightly convex ventrally. no tendency to develop a midline contact The basioccipital and the basisphenoid are with its opposite element. In keeping with fused, as no suture can be delimited between the moderate narial retraction, the dorsal pro- the two elements. Like in many extant scin- cess of the maxilla rises above the middle coids, the ¯oor is narrow at the base of the level of the tooth row. The process is roughly basipterygoid processes, strongly widened at triangular, and bends medially to form a fa- the level of the spheno-occipital tubercles, cial ``table'' together with the nasal and pre- and narrow posteriorly at the base of the oc- frontal. The posterior process forms the lat- cipital condyle (®g. 26B). The basipterygoid eral part of the ventral border of the orbit, as process is short and laterally directed. The the jugal contributes to the medial part of the cultriform process has a short but well-ossi- border. ®ed base. The spheno-occipital tubercle is The lacrimal is apparently absent, as it greatly reduced as an extremely small knob, cannot be identi®ed on either side. The jugal and is shifted anteriorly close to the midlevel is generally boomerang-shaped. At the pos- of the braincase ¯oor. The occipital recess is teroventral corner it has a blunt, but promi- a ®ssurelike structure and is strongly oblique nent, process directed ventrally. The poster- anteroventral-posterodorsally. The occipital odorsal process is equilateral along its entire condyle is small, and is formed entirely by length without the distal narrowing seen gen- the basioccipital, with essentially no contri- erally in other lizards. It has a blunt dorsal bution from the exoccipitals. The articulation tip which contacts both the postorbital and of the exoccipital with the basioccipital is the squamosal. The anteroventral process is marked by a ridge, indicating possible fusion attached to the medial side of the posterior of the two bones. process of the maxilla, so that the jugal can- The recessus vena jugularis is greatly re- not be seen in lateral view. duced as an extremely shallow groove. The PALATAL ELEMENTS: The palatal elements crista prootica is a low crest, in keeping with are mostly well preserved. The vomers are the reduction of the recessus vena jugularis. short and seem to be paired as preserved. The posterior opening of the Vidian canal is The palatal surface of the element is tooth- very small and is located at the base of the less. The palatine is short and wide, but it basipterygoid process. Posteriorly within the lacks the characteristic scrolling seen in recessus, the facial foramen opens on the me- skinks and has no midline contact with the dial wall of the groove and just anterior to opposite side of the element. The palatine the knoblike spheno-occipital tubercle. The has a posterior process, which contacts the foramen ovale is slightly elongate and is lo- pterygoid and forms most of the medial bor- cated right above the oblique occipital recess. der of the suborbital fenestra. No palatal In dorsal view, the entire braincase is shift- teeth are developed on the ventral surface of ed posteriorly and well exposed posterior to the element. the parietal margin (perhaps a burrowing ad- The pterygoid is a typical Y-shaped bone, aptation, see Rieppel, 1981). In occipital with short anterior processes and a longer view, the paroccipital process is short and is posterior process. The anteromedial process proportionally robust. It is horizontal in pos- 82 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249 terior view, but is anterolaterally directed in ches to the relatively high lateral parapet of dorsal view, differing from the normal con- the tooth row. The crowns are poorly pre- dition in which the process is posterolaterally served, the cusp pattern cannot be clearly oriented. This feature of the paroccipital pro- viewed on the specimen. cess, seen in many extant skinks, is correlat- ed with the posterior shifting of the braincase COMPARISON AND DISCUSSION as a burrowing adaptation. The new taxon is possibly referable to the MANDIBLE: The mandible is extremely Scincoidea on the basis of the feature retroar- slender. In lateral view, the dentary is pene- ticular process in¯ected medially and broad- trated by ®ve extremely small mental foram- ened posteriorly. Within the Scincoidea, it ina. The posterior border of the dentary is shares with scincids the presence of a jugal- slightly notched for the blunt anterior process squamosal contact and expansion of the post- of the surangular. The surangular is the only frontal, but lacks any tendency toward de- element that ®ts in the dentary notch, and the veloping a secondary palate (see Estes et al., anterior part is separated from the angular 1988 for character evaluation). bone by a slender posterior ventral process A notable feature of the skull is that the of the dentary. This condition is similar to prefrontal contacts the postfrontal above the that seen in typical burrowing skinks (e.g., orbit and along the lateral border of the fron- AMNH 2245: of®cinalis; AMNH tal. Such a contact occurs homoplastically in 48509: Acontias gigracilicauda), but differs several groups of lizards, including chamae- from other scincomorphs in which normally leonids, some skinks, and some anguimorphs both the surangular and angular ®t in the (Estes et al., 1988). Whether such a condition dentary notch. seen in the new taxon is homologous to the In medial view, the subdental shelf is slen- similar condition in those skinks cannot be der but clearly de®ned, unlike the sloped determined, because of the uncertain rela- tooth-bearing border in advanced angui- tionships of the new taxon within the Scin- morphs (Anguidae and Platynota). The comorpha. Meckelian canal is narrow and largely cov- Generally, the characters discussed above ered by the splenial. The splenial is narrowly indicate a possible scincoid relationship of elongate, with its anterior extension termi- this new lizard; however, lack of other char- nating close to the mandibular symphysis acter support (see Estes et al., 1988) prevents and its posterior extension terminating below us from placing it in any of the two extant the posteroventral process of the coronoid familial groups of the Scincoidea (Scincidae bone. The anterior inferior alveolar foramen and ). Also, further work needs to and the anterior mylohyoid foramen cannot be done to resolve its relationships with other be properly identi®ed as a matter of preser- scincomorphs such as Parmeosaurus, Sla- vation. voia, Globaura, and Eoxanta. The retroarticular process is medially in- ¯ected and posteriorly widened. The most SCINCOMORPHA INCERTAE SEDIS distinctive feature of the lower jaw is the posterior notch of the retroarticular process. FAMILY INCERTAE SEDIS This notch may be functionally related to at- New genus and species (unnamed) tachment of the mandibular depressor mus- Figure 27 cles, but its actual role is unclear. To our knowledge, no other lizard known has de- SPECIMEN: IGM 3/54 (MAE 29/93-192), veloped this type of notch. incomplete skull articulated with mandibles. LOCALITY AND HORIZON: Ukhaa Tolgod, DENTITION: Marginal teeth are preserved on both sides of the upper and lower jaws, Nemegt Basin, Mongolian Gobi Desert; Up- but neither side of the jaws shows a complete per Cretaceous Djadokhta Formation. tooth row. The teeth are slenderly cylindrical, and closely spaced from one another along DESCRIPTION the tooth row. Tooth implantation is pleuro- The specimen IGM 3/54 is an incomplete dont, as about half of the tooth height atta- skull articulated with mandibles. The speci- 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 83

Fig. 27. Scincomorpha, family incertae sedis, new genus and species (unnamed): A±C, IGM 3/54, incomplete skull with mandibles, lateral, dorsal and ventral views. 84 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249 men was collected from the Gilvent Wash orbit, and obscures the greatly reduced lac- sublocality at Ukhaa Tolgod, and is pre- rimal, which is con®ned to the inner side of served in well-cemented sandstone concre- the orbital corner. The lacrimal borders a tion. This type of preservation is different small lacrimal foramen with the prefrontal, from most of the other lizard specimens from without involvement of the maxilla. Anteri- Ukhaa Tolgod, which are often preserved in orly, the premaxillary process of the maxilla poorly cemented sandstones. is short and slightly overlaps the lateral side SKULL ROOF: The premaxillae are paired of the premaxilla. No premaxillary aperture with a clear midline suture. The anterior sur- is developed at the notched suture with the face of the premaxilla is smooth, and has no premaxilla. Posteriorly, the maxilla has a anterodorsal premaxillary foramina. The na- slender process extending to the midlevel of sals are also paired, and each element later- the large and slightly elongate orbit. The pos- ally contacts the dorsal process of the max- terior end of this process ends with a small illa, but is separated from the prefrontal by a notch, which articulates with the jugal (®g. frontal process (®g. 27B). The frontals are 27A). Such an articulation occurs in some fused and strongly narrowed between the or- skinks (e.g., AMNH 140794: Corucia zebra- bits. The subolfactory processes of the fron- ta; AMNH 27296: queen- tals are not exposed, but the impressions of slandae), but is highly variable in other the posterior part of the frontals show the skinks (e.g., AMNH 57864: schnei- processes are well developed and may well deri; AMNH 99684: Tiliqua nigrolutea). have a midline contact below the olfactory The jugal is a lightly built element without tract. a posteroventral process. It has an elongate The parietal is incompletely preserved. It anteroventral process, which extends along appears to have had a short and rectangular the medial side of the posterior process of table, and proportionally long supratemporal the maxilla and hence is not exposed in lat- processes. Although the table is incomplete, eral view. The posterodorsal process is ex- impressions show a parietal foramen is pres- tremely slender but forms a complete post- ent at the center of the table. The lateral bor- orbital bar. As the squamosal is not preserved der of the parietal table is not ¯anged, indi- on both sides it can not be determined wheth- cating a ventral origin of the temporal mus- er a jugal-squamosal contact was present. cles. PALATAL ELEMENTS: Some palatal elements The prefrontal anteriorly sutures with the can be identi®ed in ventral view. The vomers posterior border of the dorsal process of the are poorly preserved, and whether the two maxilla. Medially, the bone contacts the fron- sides are fused or separate cannot be deter- tal only and is separated from the nasal by a mined. The palatines are short and wide, and frontal-maxilla contact. The postfrontal and are toothless. The two sides are very close to the postorbital are completely fused as a sin- the midline, and together with the pterygoids gle element (i.e., postorbitofrontal). Such fu- strongly restrain the interpterygoid vacuity as sion occurs in six extant groups (see Estes et a narrow recess. The pterygoids have an al., 1988 for discussion), and its phylogenetic oblique suture articulation with the palatine signi®cance is equivocal among squamate at the midlevel of the suborbital fenestra, and taxa. On IGM 3/54, the posterior process of form part of the posterior border of the fe- the postorbitofrontal is very short, and thus nestra together with the ectopterygoid. Like the upper temporal bar may be largely the palatines, the pterygoids are also tooth- formed by a strongly elongated squamosal less (®g. 27C). (not preserved on both sides). MANDIBLE: The mandibles are completely The maxilla is well preserved on both preserved on both sides (®g. 27C). The lower sides. The nasal process of the maxilla is jaw is relatively heavily built in relation to primitively located above the anterior part of the skull. The lateral surface of the dentary the tooth row, and the lateral surface of the is smooth, without any trace of ornamenta- process appears to be ornamented with light tion. Sutures between the dentary and coro- dermal rugosities (®g. 27A). The maxilla noid can be identi®ed, but the dentary-sur- forms a large part of the ventral border of the angular suture cannot be delimited because 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 85 of fusion. The posterodorsal part of the den- pleurodont, although they are not exposed in tary seems to have a small notch for the an- medial view. terior process of the surangular bone. The coronoid bone is small, and its weakly de- COMPARISON AND DISCUSSION veloped dorsal process is anteriorly over- lapped by the coronoid process of the den- Morphologically, the specimen (IGM 3/ tary bone. The coronoid is laterally exposed 54) shows a unique mosaic of characters. as a small wedge between the dentary and Presence of frontal fusion and interorbital the surangular as in most other scincomorphs constriction seems to indicate an iguanian af- (see Estes et al., 1988 for evaluation). The ®nity, but many other character states such anterior surangular foramen is small and lo- cated on the surangular behind the base of as presence of the parietal foramen near the the coronoid dorsal process. The posterior center of the parietal table and a ventral or- surangular foramen is barely identi®able and igin of the temporal musculature indicate that probably located anteroventral to the cran- the above-mentioned character states are ho- iomandibular joint. The surangular-prearticu- moplastic relative to similar conditions in ig- lar suture is recognizable on the posterior uanians. On the other hand, fusion of the part but anteriorly blurred because of fusion. frontals with descending processes in contact The retroarticular process is slender and below the olfactory tract suggests a gekkotan straight, nonde¯ected, and medially carries af®nity of this lizard; however, this possible no angular process or prearticular crest. af®nity is disproved by other character states Medially, the splenial is reduced to cover (see below). the posterior two thirds of the Meckelian ca- Despite the above-mentioned uncertain- nal. The anterior one third of the canal tends ties, the unnamed new taxon is referred to to be closed, but remains open as a narrow the Scincomorpha based on a combination of and medially faced ®ssure. The posterior ex- the following features: the nasal and prefron- tension of the splenial reaches at least the tal are separated by an anterolateral process level of the posteroventral process of the cor- of the frontal; origin of the adductor muscle onoid bone, but its actual extent cannot be is on the ventral aspect of the parietal; and identi®ed because of fusion with the prear- the coronoid is laterally exposed as a small ticular. The anterior inferior alveolar foramen wedge between the dentary and the suran- and the anterior mylohyoid foramen are close gular. Within the Scincomorpha, two char- to one another, and both lie at a level about acter states (paired premaxillae, and nearly two thirds of the way back along the tooth closed Meckelian canal by dentary with row. The anterior part of the angular can be strong reduction of the splenial) seem to in- delimited as a very slender splint, but it is dicate a possible af®nity of the new taxon to posteriorly fused with the prearticular and the Scincoidea; however, a slender and the surangular. straight retroarticular process disproves this DENTITION: The paired premaxillae carry a af®nity. total of nine ®ne teeth (the right side has ®ve and the left side four). The left maxilla car- The species is known from a single and ries about 22 teeth, and the tooth row pos- relatively poorly preserved specimen, and teriorly extends to the midlevel of the orbit. there is still much to learn about this lizard The teeth are extremely tiny, simple and peg- before a con®dent taxonomic assignment can like, and closely spaced from one another. be made. For this reason, we leave the genus This type of dentition, in keeping with the and species unnamed, and hence, no type relative small size of the skull, indicates the designation and diagnosis are provided. lizard may have fed largely on . The low- However, the following character states are er dentition cannot be exposed for observa- potential autapomorphies of this species: tion; however, the number of dentary teeth fused frontals are extremely narrow; margin- can be estimated at 22-24, as the dentary nor- al teeth are extremely ®ne and closely ar- mally carries a few more teeth than the max- ranged along the tooth row; postdentary illa. All the marginal teeth are presumably bones are partially fused in the lower jaw. 86 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249

Slavoia darevskii Sulimski, 1984 and Scincidae.'' We interpret that this state- Figure 28 ment implies a possible Slavoia darevskii- Scincidae sister group relationship. More re- HOLOTYPE: ZPAL MgR-I/8, skull with cently, Alifanov (1993a) without explanation mandibles and postcranial skeleton. listed Slavoia darevskii under the Acontiidae, TYPE LOCALITY AND HORIZON: Khulsan, which is commonly treated as a subfamily in Mongolian Gobi Desert; Upper Cretaceous the Scincidae (Greer, 1970; Estes, 1983; Es- Barun Goyot Formation. tes et al., 1988). KNOWN DISTRIBUTION: Djadokhta Forma- In terms of skull morphology, Slavoia dar- tionÐUkhaa Tolgod locality; Barun Goyot evskii shares a single palatal character state FormationÐKhulsan and Khermeen Tsav lo- with the acontine skinks (ectopterygoid con- calities (Sulimski, 1984; this paper). tacts palatine anteriorly and posteriorly, ex- REVISED DIAGNOSIS: Scincomorph lizard cluding maxilla and pterygoid from entering differing from other members of the group the suborbital fenestra), but lacks many de- in having the following derived character rived character states of the latter group (e.g., states: skull very short and wide; nasal-pre- loss of limbs, loss of supratemporal arch, frontal contact lost owing to widening of prefrontal and squamosal reduced, and frontals; signi®cantly wide frontals; great re- Meckelian canal closed with fusion). Pres- duction of orbit into narrow teardrop-shaped ence of palatine scrolling indicates that the opening; parietal foramen rudimentary or en- taxon may be scincid related, but lack of oth- tirely closed; prefrontal-postfrontal contact er features (such as the jugal-squamosal con- forming medial rim of orbit; anteroventral tact) may prevent classifying Slavoia darev- process of jugal nearly lost; strong reduction skii in the Scincidae. The relationships and in number of marginal teeth, with short en- classi®cation of Slavoia darevskii within the tirely antorbital maxillary tooth row; subor- Scincomorpha remain ambiguous, pending bital fenestra strongly reduced; ectopterygoid thorough phylogenetic study of this highly contacts palatine anteriorly and posteriorly, specialized form and its likely relatives. excluding both maxilla and pterygoid from entering suborbital fenestra. Globaura venusta Borsuk-Bialynicka, 1988 REFERRED SPECIMENS: Ukhaa TolgodÐ Figure 29 IGM 3/145 (MAE 96-1), nearly complete skull with mandibles and partial postcranial HOLOTYPE: ZPAL MgR-III/40, incomplete skeleton (®g. 28C); IGM 3/146, incomplete skull with mandibles. skull with mandibles and articulated postcra- TYPE LOCALITY AND HORIZON: Khermeen nial skeleton (®g. 28D); 3/147±3/153 (MAE Tsav, Mongolian Gobi Desert; Upper Creta- 178/92-21, 160/93-40, 95-7, 94-66-1, 94-66- ceous Barun Goyot Formation. 2, 94-66-3, 94-66-4), all incomplete skull KNOWN DISTRIBUTION: Barun Goyot For- with mandibles (total: 9 specimens from mationÐKhermeen Tsav and Khulsan local- Ukhaa Tolgod). KhulsanÐIGM 3/154 (MAE ities (Borsuk-Bialynicka, 1988; this paper); 63), nearly complete skull with mandibles Djadokhta FormationÐBayn Dzak and and partial postcranial skeleton (®g. 28A, B); Ukhaa Tolgod (this paper). Khermeen TsavÐIGM 3/155±3/159 (MAE DIAGNOSIS: ``Small non-teiioid lacertoid 175/92-21, 176/92-21, 181/92-21, 185/92-21, with paired premaxillae, and frontals fused 198/92-25), all incomplete skulls with man- and constricted. Ratio of minimum frontal dibles (total: 5). width/sagittal length 0.16-0.19. Postfrontal REMARKS: Although Sulimski (1984) sug- posterior extension subject to variability. No gested that a relationship of Slavoia darevskii osteoderms. Snout/skull length ratio 0.3- with the gymnophthalmine teiids ``seems to 0.33. Ratio of length of tooth row underlying be more probable,'' he made no formal fa- orbit/orbit length 0.18-0.27'' (generic diag- milial assignment of this taxon. Borsuk-Bi- nosis of Borsuk-Bialynicka, 1988: 214). alynicka (1991a: 10) ambiguously stated that ``Skull length 14-25 mm. Modal skull ``Eoxanta, and possibly Slavoia darevskii, length of 21.5 mm, as in holotype. Postfron- become sister groups of both Xantusiidae tal rarely extends posteriorly more than half 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 87

Fig. 28. Scincomorpha, family incertae sedis, Slavoia darevskii: A, B, IGM 3/154, incomplete skull with mandible and partial postcranial skeleton from Khulsan, dorsal and ventral views; C, IGM 3/145, nearly complete skull with mandibles and partial postcranial skeleton from Ukhaa Tolgod, dorsal view; D, IGM 3/146, incomplete skull with mandibles and articulated postcranial skeleton from Ukhaa Tolgod, dorsal view. 88 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249

Fig. 29. Globaura venusta: A±C, IGM 3/164, nearly complete skull with mandibles from Khulsan, dorsal, ventral, and right lateral views; D±F, IGM 3/160, nearly complete skull with mandibles from Ukhaa Tolgod, dorsal, ventral, and left lateral views. 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 89

the length of the parietal table. Otic regions KNOWN DISTRIBUTION: Ukhaa Tolgod and of the brain case globose'' (speci®c diagnosis Khermeen Tsav localities; Djadokhta and Ba- of Borsuk-Bialynicka, 1988: 215). run Goyot formations. REFERRED SPECIMENS: Ukhaa TolgodÐ DIAGNOSIS: ``Small xantusiid-like lacertoid IGM 3/160 (MAE 95-89), nearly complete with paired premaxillae; parietal not extend- skull with mandibles; IGM 3/161±3/163 ed to cover dorsal aspect of the braincase; (MAE 21/93-176, 95-24, 95-40), all incom- frontals fusing late in ontogeny, provided plete skulls with mandibles. KhulsanÐIGM with ventral sagittal crest partly separating 3/164 (MAE 217/92-61), nearly complete olfactory tracts. Ratio of minimum frontal skull with mandibles. Khermeen TsavÐIGM width/sagittal length 0.38. Ectopterygoid 3/165±3/167 (MAE 173/92-21, 172/92-21, massive, shifted anteriorly to parallel the pal- 183/92-21), all incomplete skulls with man- atine borders the slit-like suborbital fenestra. dibles. Postfrontal extending posteriorly to close the REMARKS: Borsuk-Bialynicka (1988) de- supratemporal fenestra. Postorbital and squa- scribed Globaura venusta and classi®ed it in mosal dorsoventrally ¯attened, bandlike. Os- the Lacertoidea. Later, Alifanov (1993a) list- teoderms present in some specimens. Snout/ ed this species under the with- skull length ratio 0.23-0.26. Ratio of length out explanation. There is little doubt about of tooth row underlying orbit/orbit length al- its af®liation with the Scincomorpha, but the most 0'' (Borsuk-Bialynicka, 1988: 222). relationships of Globaura venusta to other REFERRED SPECIMEN: IGM 3/168 (MAE scincomorphs are far from clear. Presence of 95-90), incomplete skull with mandibles, interdigitation of the frontoparietal suture from Ukhaa Tolgod (sublocality Camel (®g. 29A, D) is the single character state sup- Humps). porting the referral of Globaura venusta to REMARKS: The general proportions of the the Lacertiformes, based on the phylogenetic skull (IGM 3/168) are identical to the holo- framework provided by Estes et al. (1988). type of Eoxanta lacertifrons (ZPAL MgR- Two other character states (pyriform recess III/37). The two specimens are similar in narrow throughout most of its length, and fa- several respects: the snout is short and wide; cial region elongated and snout region lat- the frontals are paired and have parallel lat- erally compressed) are incorrectly described eral borders anteriorly; and the parietal table for this species (®g. 29). Lack of a pterygoid is roughly square (Borsuk-Bialynicka: sub- lappet of the quadrate and a nonin¯ated man- quadrangular) with a small parietal foramen dibular fossa are two other features that dis- in the center. On the basis of these similari- prove the close relationship of Globaura ven- ties, the new specimen can be referred to usta with the Lacertiformes. The enlarged Eoxanta lacertifrons. However, the new postfrontal can be interpreted as either a lac- specimen shows a different frontoparietal su- ertid or scincid feature, while fused and con- ture pattern than the holotype. The suture on stricted frontals, and the presence of a jugal- the holotype is described as ``straight as a squamosal contact ambiguously suggest pos- whole but ®nely interdigitating with a slight sible relationships with either the Teiidae or suggestion of frontal tabs'' (Borsuk-Bialyni- the Scincidae. Because of con¯icting evi- cka, 1988: 223). IGM 3/168 shows a non- dence, we tentatively place Globaura ven- interdigitating zigzag suture, with well-de- usta in the Scincomorpha without further re- ®ned parietal tabs. Whether the difference is ferral to any subgroup. the result of individual variation or specimen preservation cannot be determined due to the Eoxanta lacertifrons Borsuk-Bialynicka, small sample size. Also, the postfrontals of 1988 the holotype are enlarged tending to enclose the supratemporal fenestra, whereas the new HOLOTYPE: ZPAL MgR-III/37, incomplete specimen from Ukhaa Tolgod has only a skull with mandibles. small part of the element preserved on both TYPE LOCALITY AND HORIZON: Khermeen sides. These uncertainties make the referral Tsav, Upper Cretaceous Barun Goyot For- of the new specimen to Eoxanta lacertifrons mation. tentative. 90 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249

ANGUIMORPHA FUÈ RBRINGER, 1900 rate; descending process of parietal subrect- angular and laterally compressed; epiptery- CARUSIOIDEA GAO AND NORELL, goid strongly oblique posterodorsally; 1998 marginal process of supraoccipital prominent CARUSIIDAE BORSUK-BIALYNICKA, and well ossi®ed; presence of strong adduc- 1987 tor crest dorsolaterally on surangular; mar- Carolinidae Borsuk-Bialynicka, 1985: 153 ginal teeth extremely ®ne, large in number, and having comblike arrangement; strong Carusia intermedia Borsuk-Bialynicka, 1987, posterior extension of neural spine of axis nom. subst. over entire third cervical (see Gao and No- [pro Carolina Borsuk-Bialynicka, 1985 rell, 1998). (non Thomson, 1880)] REFERRED SPECIMENS: IGM 3/16±3/23 Figure 30 (MAE 95-5, 95-52, 94-38, 40/93-90, 94-26, 96-9, 96-122, 96-191), all nearly complete HOLOTYPE: ZPAL MgR-III/34, incomplete skull with mandibles. skulls with mandibles; IGM 3/24±3/47 (MAE 35/93-167, 115/93-93, 241/93-130, TYPE LOCALITY AND HORIZON: Khermeen Tsav, Nemegt Basin, Mongolian Gobi De- 104/93-158, 33/93-167, 470/93-134, 92/93- sert; Upper Cretaceous Barun Goyot For- 104, 231/93-99, 414/93-111, 311/93-127, 36/ mation. 93-129, 314/93-127, 37/93-129, 94-27, 94- 49-1, 94-101, 95-72, 96-17, 96-40, 96-50, KNOWN DISTRIBUTION: Djadokhta Forma- tionÐBayn Dzak, Bayan Mandahu, Ukhaa 96-52, 96-65, 96-109, 96-196), all incom- Tolgod localities (Gao and Hou, 1996; this plete skulls with mandibles; IGM 3/48±3/50 paper); Barun Goyot FormationÐKhermeen (MAE 94-49-2, 95-51, 61/93-130), all in- Tsav and Khulsan (Borsuk-Bialynicka, complete mandibles. The above-enumerated 1985). specimens (total: 35) are all from Ukhaa Tol- DIAGNOSIS: Sharing with extant xenosaur- god and adjacent localities. ids the following derived character states: In addition, two incomplete skulls with frontals fused and constricted between orbits; mandibles IGM 3/51 and 3/52 (MAE 67, 71) presence of jugal-squamosal contact; pres- represent the only specimens of Carusia in- ence of dermal vermiculate rugosities on termedia from the classic Bayn Dzak (Flam- skull roof elements; postorbital branch of ju- ing Cliffs) locality. gal ornamented. REMARKS: Although noticing some simi- Distinguished from all other closely relat- larities shared by Carusia intermedia with ed taxa including and Shinisau- the xenosaurids, Borsuk-Bialynicka (1985) rus by the following autapomorphies: lacri- originally classi®ed the Gobi lizard in the mal absent, with anteroventral process of ju- Carusiidae and referred it to the family gal contacting prefrontal; caudoventral pro- ?Scincomorpha. Later, the same author (Bor- cess of jugal ventrally directed; fenestra suk-Bialynicka, 1991a) regarded the family exochoanalis distinctively short and elliptic; as ``either a sister-group of the Xenosauridae presence of midline contact of palatines an- or an autarchoglossan taxon convergent to teriorly; palatine rectangular and strongly this family.'' widened, suppressing suborbital fenestra into Recently, new specimens of this phyloge- narrow and elongate opening; presence of netically signi®cant lizard species were col- vertical crest anteriorly on quadrate; condyle- lected from Bayan Mandahu (Gao and Hou, fossa articulation for both squamosal and su- 1996), and from Ukhaa Tolgod and adjacent pratemporal with cephalic condyle of quad- localities (Gao and Norell, 1998). The large

→ Fig. 30. Anguimorpha, Carusiidae, Carusia intermedia: A, IGM 3/16, skull with mandibles in dorsal view; B, IGM 3/25, palatal view; C, D, IGM 3/17, skull with mandibles, dorsal and ventral views; E, F, IGM 3/18, skull with mandibles, dorsal and ventral views. 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 91 92 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249 number of exquisitely preserved specimens vertebrae absent (Hoffstetter and Gasc, (®g. 30) from Ukhaa Tolgod provided im- 1969). portant material for a thorough taxonomic re- REMARKS: Camp (1923) included Varano- vision and re-appraisal of the phylogenetic idea and Mosasauroidea in his Platynota. relationships of Carusia intermedia; and re- McDowell and Bogert (1954) used the term sults of previous analysis place Carusia in- Platynota as an alternate name for Varano- termedia as the basal member of the Caru- idea, and a similar usage is seen in other pub- sioidea, which in turn occupies the most bas- lications (e.g., Rieppel, 1980a, 1988; Estes, al position within the Anguimorpha (see Gao 1983; Borsuk-Bialynicka, 1984). Lee (1997: and Norell, 1998). 78) provided a stem-based de®nition of the Platynota: ``, Lanthanotus and PLATYNOTA CAMP, 1923 Varanus, and all taxa more closely related to these forms than to other anguimorphs.'' On DEFINITION: The taxon Platynota refers to the basis of a recent analysis of 105 charac- a clade that includes the most recent common ters across 30 ingroup and three outgroup ancestor of Monstersauria and , taxa, Gao and Norell (1998) rede®ned the and all its descendants (see Gao and Norell, group as the most recent common ancestor 1998). of Monstersauria and Varanidae, and all its DIAGNOSIS: The clade Platynota is diag- descendants. This de®nition is close to nosed by an array of derived characters in- Camp's (1923) original usage. The mono- cluding: presence of plicidentine infolding at phyly of the Platynota is supported by a long marginal tooth bases (McDowell and Bogert, list of derived characters. 1954); marginal teeth widely spaced with ex- panded tooth bases (McDowell and Bogert, MONSTERSAURIA NORELL AND GAO, 1954); replacement teeth developed posteri- 1997 orly without presence of resorption pits (Rieppel, 1978); maxillary tooth row entirely DEFINITION: A clade that includes the last antorbital or slightly suborbital by no more common ancestor of Gobiderma and Helo- than three tooth positions (McDowell and derma, and all its descendants (see Norell Bogert, 1954; Gao and Norell, 1998); vomer and Gao, 1997). strongly elongate approaching level of pos- DIAGNOSIS: This robust platynotan clade is terior end of tooth row (Pregill et al., 1986); diagnosed by the following derived character palatal shelf of vomer narrow (Pregill et al., states: anterior extension of supratemporal 1986); palatine equally wide as long (Riep- reaches level of apex of parietal notch pel, 1980a); ectopterygoid in palatal view (equivocal); pterygoid lappet of quadrate contacting palatine and excluding maxilla present (unequivocal, Estes et al., 1988); an- from entering suborbital fenestra (Rieppel, terolateral process of pterygoid extends dor- 1980a; Estes et al., 1988); development of sally on ectopterygoid to contact jugal (un- intermandibular hinge (McDowell and Bog- equivocal); cephalic osteoderms fragmented ert, 1954); surangular blunt anteriorly in lat- and thickened as subconical mounds (un- eral view (Rieppel, 1980a; Pregill et al., equivocal, McDowell and Bogert, 1954); 1986); posterior extension of splenial termi- dermal rogosities present with conspicuously nates anterior to or below the coronoid em- pitted surfaces (McDowell and Bogert, 1954; inence (Estes et al., 1988); splenial-dentary equivocal); neural spines narrow and tall suture loose, with much connective tissue be- (Pregill et al., 1986; Norell and Gao, 1997; tween the two bones (Pregill et al., 1986); unequivocal); foramen ovale located anterior anterior process of coronoid elongated and to the spheno-occipital tubercle (Norell and extensively exposed dorsally (Estes et al., Gao, 1997). 1988); medial exposure of angular extensive, REMARKS: The taxonomic treatment and vertically suturing with splenial (McDowell the phylogenetic relationships of this impor- and Bogert, 1954); cervical intercentrum su- tant platynotan clade was discussed by No- tures to posterior part of preceding centrum rell and Gao (1997). The Monstersauria, in- (Rieppel, 1980a, 1980b); autotomy on caudal cluding the Helodermatidae and 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 93

Fig. 31. Anguimorpha, Monstersauria, Gobiderma pulchrum: A, B, IGM 3/55, nearly complete skull with mandibles from Udan Sayr, dorsal and ventral views. its closely related fossil taxa, forms the most but sometimes fusing with individual age. basal platynotan clade (see Gao and Norell, Posterolateral extensions of parietal close an 1998); and the monophyly of the group is angle of about 130Њ. An angle between par- well supported (see above). occipital processes is only slightly less than this. Position of lacrimal foramen changing Gobiderma pulchrum Borsuk-Bialynicka, from prefrontolacrimal suture to lacrimal sur- 1984 face. Number of tooth positions is 11 on Figure 31 maxilla, 4 on premaxilla, 10 on dentary. Os- teodermal skull covering of small-plate type HOLOTYPE: ZPAL MgR-III/64, incomplete skull with mandibles. or variable (anterior to the orbit)'' (Borsuk- TYPE LOCALITY AND HORIZON: Khermeen Bialynicka, 1984: 41). Tsav II, Upper Cretaceous Barun Goyot For- REFERRED SPECIMENS: Udan SayrÐIGM 3/ mation, Mongolian Gobi Desert. 55 (MAE 96-162), nearly complete skull KNOWN DISTRIBUTION: Khermeen Tsav II with mandibles from Udan Sayr; Ukhaa Tol- (Borsuk-Bialynicka, 1984), Udan Sayr and godÐIGM 3/56±3/58 (MAE 68/93-45, 220/ Ukhaa Tolgod (this paper) localities; Barun 93-248, and 95-29), all incomplete skulls Goyot and Djadokhta formations. Unde- with mandibles; Khermeen TsavÐIGM 3/59 scribed material is also known from Bayan (MAE 254/92-33), partial skull with postcra- Mandahu (K. Gao, personal obs.). nial skeleton; KhulsanÐIGM 3/60 (MAE DIAGNOSIS: ``Skull subpentagonal in out- 96-149), incomplete skull with mandibles. line, its larger part posterior. Frontal paired REMARKS: Borsuk-Bialynicka (1984) 94 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249

Fig. 32. Anguimorpha, Estesia mongoliensis: IGM 3/14 (holotype), nearly complete skull with man- dibles from Khulsan (courtesy of L. Meeker and C. Tarka). named and described Gobiderma pulchrum this taxon, and a revised diagnosis, will be (original spelling: Gobiderma pulchra; nom. presented elsewhere. correct. in Norell et al., 1992), and classi®ed it as ``Necrosaurian grade'' within the Pla- Estesia mongoliensis Norell et al., 1992 tynota (family uncertain). Alifanov (1993a) Figure 32 listed Gobiderma in Necrosauridae without HOLOTYPE: IGM 3/14, a well-preserved explanation. Lee (1997) grouped Gobiderma skull with mandible. with Parviderma in the Gobidermatidae. A TYPE LOCALITY AND HORIZON: Lizard Hill, recent phylogenetic analysis, however, Khulsan, (43Њ29Ј19ЉN, 101Њ08Ј44ЉE); Upper showed that Gobiderma is the basal taxon of Cretaceous Barun Goyot Formation, Mon- the Monstersauria (Norell and Gao, 1997). golian Gobi Desert. This hypothesis is supported by results from KNOWN DISTRIBUTION: Khulsan, Khermeen our more recent analyses using additional Tsav, Ukhaa Tolgod, and Bayn Dzak locali- data and a more sophisticated outgroup anal- ties (Norell et al., 1992; Norell and Gao, ysis (Gao and Norell, 1998). 1997; this paper); Djadokhta and Barun Goy- New specimens collected by the Mongo- ot formations. lian Academy of Sciences±American Muse- DIAGNOSIS: Distinguished from Heloderma um of Natural History Expeditions include and its fossil relatives by the following au- material not only from the type Khermeen tapomorphies: presence of a distinct single, Tsav area (IGM 3/59) but from Ukhaa Tol- median palatal trough formed by vomers; god and adjacent localities. IGM 3/55 (®g. long median contact of vomers; presence of 31) from Udan Sayr represents the best spec- extensive convex surface medial to posterior imen known for this taxon, and provides ridge on posterior surface of quadrate; no valuable information for understanding the distinct articular; foramen ovale located far skull morphology and relationships of this anterior to spheno-occipital tubercle; spheno- Gobi lizard taxon (see Gao and Norell, occipital tubercle strongly elongate and pos- 1998). Complete redescription of the skull of terolaterally oriented (for characters shared 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 95 with its closely related taxa see discussion in lar constriction of vertebrae present (Estes et Norell and Gao, 1997). al., 1988). REFERRED SPECIMENS: IGM 3/15, partial REMARKS: The Varanoidea include the ex- skeleton with well-preserved braincase from tant familial group Varanidae (Varanus and Khermeen Tsav; IGM 3/169 (MAE 17/93- Lanthanotus) and three fossil taxa (Chermi- 184), incomplete mandibles with teeth from notus, , and Telmasaurus). Another Ukhaa Tolgod; additional specimens have fossil taxon, Palaeosaniwa, known from been collected from Bayn Dzak, Djadokhta fragmentary jaws and vertebrae, shares with Formation (Norell and Gao, 1997). the group at least one character state: pre- REMARKS: On the basis of a nearly com- condylar constriction of vertebrae; and plete skull with mandibles from Khulsan (®g. hence, could well be a member of the group 32), Norell et al. (1992) named and described (see discussion in Gao and Norell, 1998). Estesia mongoliensis, and provided alterna- tive hypotheses in which Estesia mongolien- Cherminotus longifrons sis could be grouped with either the Varani- Borsuk-Bialynicka, 1984 dae or the Helodermatidae (see also Lee, Figure 33 1997). Additional specimens were later re- covered from Khermeen Tsav and Ukhaa HOLOTYPE: ZPAL MgR-III/59, incomplete Tolgod, including a well-preserved braincase skull with mandibles missing. with partial postcranial skeleton (IGM 3/15), TYPE LOCALITY AND HORIZON: Khermeen and incomplete mandibles with teeth (IGM Tsav, Gobi Desert; Upper Cretaceous Barun 3/169). Discovery of the braincase (IGM 3/ Goyot Formation. 15) revealed pivotal evidence for clarifying KNOWN DISTRIBUTION: Barun Goyot For- the phylogenetic position of Estesia mongo- mationÐKhermeen Tsav (Borsuk-Bialyni- liensis. Recent analyses using a different data cka, 1984; Alifanov, 1993a); Djadokhta For- set and different outgroup rooting indicate mationÐUkhaa Tolgod and Tugrugeen Shi- that the taxon is the sister group to the Hel- reh localities (this paper). odermatidae in a clade named the Monster- DIAGNOSIS: ``A small-sized lanthanotid not (see Norell and Gao, 1997; Gao and attaining 3 cm of skull length with relatively Norell, 1998). long and slender snout and non-elongated pa- rietal. Parietal foramen present. Vomers rel- atively long and slender. Teeth number very VARANOIDEA CAMP, 1923 low. Basal ¯uting present but not very com- plicated'' (Borsuk-Bialynicka, 1984: 60; see DEFINITION: The most recent common an- below for comments). cestor of Telmasaurus and Varanidae, and all REFERRED SPECIMEN: IGM 3/170 (MAE its descendants. The term Varanoidea as de- 24/93-26), incomplete skull with mandibles ®ned by Gao and Norell (1998) differs from and partial postcranial skeleton, from Tug- the usage of previous authors (e.g., McDow- rugeen Shireh. ell and Bogert, 1954; Rieppel, 1980a; Estes, REMARKS: Although known from several 1983; Pregill et al., 1986; Estes et al., 1988), specimens from the Gobi, the skull mor- who in most cases used Varanoidea as alter- phology of Cherminotus longifrons is poorly native name for Platynota (see also Lee, understood. Consequently, published diag- 1997). noses are inadequate. Besides the generic di- DIAGNOSIS: The Varanoidea as de®ned agnosis (see above), Borsuk-Bialynicka above can be unambiguously diagnosed by (1984: 61) provided a species diagnosis as the following derived character states: subol- follows: ``frontal to parietal length ratio is factory processes of frontals closely ap- about 1.5 in sagittal axis. Five widely spaced proach or contact posteromedially (McDow- conical teeth in the maxilla.'' However, none ell and Bogert, 1954); entocarotid fossa with- of these characters are diagnostic of the tax- in recessus vena jugularis absent (McDowell on and this diagnosis needs to be revised. For and Bogert, 1954); posterior lacrimal fora- example, the holotype specimen is described men double (Pregill et al., 1986); precondy- as having an extra anterior surangular fora- 96 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249

Fig. 33. Anguimorpha, Varanoidea, Cherminotus longifrons: A, B, IGM 3/170, incomplete skull with mandibles and cervical vertebrae from Tugrugeen Shireh, dorsal and lateral views. men below the coronoid (Borsuk-Bialynicka, arch is complete, having a slender and elon- 1984: 66); if the observation is justi®ed, this gated squamosal that extends far anterior to unique feature should be included in the di- contact the postorbital (contra Borsuk-Bi- agnosis. alynicka, 1984: ®g. 17). Another important Phylogenetically, Cherminotus longifrons feature concerns the number of lacrimal fo- was grouped with Lanthanotus within the ramina (see discussion below), but like the Varanidae (Borsuk-Bialynicka, 1984; Gao supratemporal arch, the actual condition is and Norell, 1998). The new material from uncertain from previously known specimens. Tugrugeen Shireh, however, provides signif- As shown on the new specimen (see ®g. 33), icant data that may well challenge this inter- Cherminotus longifrons has a single lacrimal pretation. One phylogenetically signi®cant foramen. Also, contrary to the original de- feature concerns the supratemporal arch, scription of the teeth as conical, well-pre- which is not preserved on the holotype, yet served teeth on the new specimen are tren- was suggested to be incomplete. The new chant, laterally compressed, and recurved. A specimen (IGM 3/170) clearly shows that the complete redescription of this taxon based on 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 97 this material, which will result in a determi- ever, a pair of posterior premaxillary foram- nation of its phylogenetic position, will be ina are developed laterally at the base of the presented elsewhere. All that will be added premaxillary spine (®g. 34). The nasals are here is that grouping Cherminotus with Lan- paired, as indicated by the clear midline su- thanotus is unsupported by any character ev- ture anteriorly and the articular surface at the idence. midline on the posterior part of the right el- ement. Aiolosaurus oriens, new genus and species In ventral view, the premaxillae have a Figure 34 pair of short vomeromaxillary processes, which are separated from one another along ETYMOLOGY: aiolos (Gr.), god of the the midline. The process posteriorly under- winds; oriens (L.), east. lies the vomer. Anteriorly at the base of the HOLOTYPE: IGM 3/171 (MAE 283/93- processes, the incisive process of the pre- 108), incomplete skull with mandibles and maxillae is well developed and is only slight- partial postcranial skeleton. ly bipartite posteriorly by a small groove. No TYPE LOCALITY AND HORIZON: Ukhaa Tol- ventral premaxillary foramen can be identi- god (between Xanadu and First Strike), Ne- ®ed, but a notch on the lateral border of the megt Basin, Mongolian Gobi Desert; Upper vomeromaxillary process forms the medial Cretaceous Djadokhta Formation (Loope et rim of the aperture between the premaxillae al., 1998). and the maxilla. The vomers are strongly KNOWN DISTRIBUTION: Only known from elongate as a narrow band, and have a the type locality and horizon. straight midline sutural contact. As seen in DIAGNOSIS: Distinguished from Chermi- other varanoids, the vomer extension reaches notus longifrons and other closely related to the level of the posterior end of the max- varanoids by the following character states: illary tooth row. A single vomerine aperture nasals paired; presence of aperture between is developed anteromedially behind the pre- premaxilla and maxilla; anteromedial process maxilla-vomer articulation and close to the of maxilla separating premaxilla from sep- midline suture of the vomers. tomaxilla; dorsal septomaxillary foramen The prefrontal is preserved on the right strongly reduced and close to midline; ante- side of the skull. It has an extensive sutural rior surangular foramen opening in distinct contact with the frontal medially, but anter- groove ventral to apex of coronoid process. omedially is separated from the anterior pro- cess of the frontal and the nasal by a narrow DESCRIPTION gap, as seen in other platynotans. The pre- The type and only known specimen IGM frontal has an elongate posterior extension, 3/171 (MAE 283/93-108) consists of a par- which at least extends to the midlevel of the tial skull with both mandibles and partial orbit. However, whether the prefrontal con- postcranial skeleton. The preserved skull el- tacted the postfrontal cannot be determined. ements include the premaxillae, septomaxil- The anteroventral process of the prefrontal la, right nasal, right maxilla with teeth, right laterally sutures with the well-developed lac- frontal and prefrontal, right lacrimal, quad- rimal, which forms the anteroventral border rate, squamosal, and supratemporal. The of the orbit. A single lacrimal foramen opens skull shows a strong narial retraction, as seen at the suture between the two bones. How- in other varanoids. Both left and right man- ever, the contribution of the prefrontal to the dibles are preserved. orbitonasal fenestra is unknown because of SKULL ELEMENTS: The premaxillae are breakage in the specimen. fused as a single unit. It has a slender and The right maxilla is completely preserved. elongate spine that slightly intervenes the an- It has a low nasal process, and is roughly terior part of the nasals. The anterior surface triangular in lateral view, despite the strong of the premaxilla is smooth, and has no an- narial retraction. Anteriorly, the bone has a terior dorsal premaxillary foramina (as op- slender but well-developed premaxillary pro- posed to Varanus, see Bahl, 1937; personal cess and anteromedial process; between these obs. of AMNH-DVP-CA 1201, 2994). How- two processes opens a premaxillary aperture 98 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249

Fig. 34. Anguimorpha, Varanoidea, Aiolosaurus oriens, new genus and species: A±C, IGM 3/171, incomplete skull with mandibles from Ukhaa Tolgod, dorsolateral, lateral and ventral views. 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 99

(®g. 34). The anteromedial process is so well eral exposure of the angular is more exten- developed that it extends behind the premax- sive than its medial side, and this is probably illa to a point where it must have contacted a primitive condition in comparison with ex- the opposite element (not preserved). In dor- tant platynotans. sal view, the dorsal maxillary foramen (an- In medial view, the subdental shelf is terior opening of the superior alveolar canal) greatly reduced as a slope of tooth-bearing opens anteromedial to the nasal process of border, as seen in other platynotans and an- the bone and is close to the maxillary-sep- guids as well. The Meckelian canal is strong- tomaxillary suture. The lateral surface of the ly reduced and open ventrally as a narrow maxilla is smooth, and is penetrated by a hor- groove below the anterior half of the tooth izontal row of six irregularly spaced lateral row. The splenial is retracted to the midpoint superior alveolar foramina. of the tooth row, but it posteriorly has a short As in extant Varanus, the septomaxillae tonguelike extension that overlaps the angu- are exposed in dorsal view. The paired ele- lar (nonvertical posterior border). The splen- ments contact one another along the midline, ial is dorsally separated from the dentary by and laterally suture with the inner border of a narrow gap, which is for connective tissue the maxilla. The dorsal surface of the bone to form a mobile articulation. The anterior is convex, and the dorsal septomaxillary fo- inferior alveolar foramen and the anterior ramen is strongly reduced as a minute open- mylohyoid foramen are closely located to ing close to the midline. one another, and both the foramina are MANDIBLES: The right mandible is nearly roughly below the last dentary tooth. complete, whereas most of the left side is The retroarticular process of the mandible missing (only the anterior part of the dentary is broken, but the preserved part clearly is preserved). The mandible is very slender, shows that the process is de¯ected medially greatly elongate, and sigmoid in lateral view as in other anguimorphs. with a strongly curved ventral border of the DENTITION: Marginal teeth are well pre- dentary and elevated border of the postden- served on the premaxillae and the right side tary region. The dentary-surangular articu- of the jaws (both the upper and lower teeth). lation of the jaw is typical platynotan type, The premaxillae bear four teeth, and spaces with the blunt anterior extension of the sur- for three others. The right maxilla has six angular terminating at the same level as the teeth and spaces for three to four others, and anterior extension of the coronoid. the maxillary tooth row is entirely anterior to The coronoid is proportionally a robust el- the orbit, as in many other platynotans. The ement. It has a strong anterodorsal process, right mandible has ®ve teeth preserved, with which rests on top of the surangular horizon- the last tooth slightly removed from its orig- tally and anteriorly clasps the dentary. Later- inal position. The teeth are widely spaced oventral to the summit of the coronoid, the from one another, and the crowns are sharply surangular develops a distinct narrow groove pointed and recurved. Tooth bases are wid- in which opens the anterior surangular fora- ened, and have weakly developed pliciden- men. The location of the anterior surangular tine infolding. The total number of dentary foramen is similar to other platynotans (Var- teeth is estimated as no more than nine, and anus, Heloderma), but the groove is probably this lower number is similar to the condition unique for this taxon among platynotans. The in Cherminotus (see above). posterior surangular foramen is a much smaller opening, which is located shortly an- COMPARISON AND DISCUSSION terior to the craniomandibular joint. The prearticular is slender and long, and The new specimen (IGM 3/171) from the dorsally has a horizontal suture with the sur- Ukhaa Tolgod locality is substantially small- angular following the contour of the jaw. The er than any of the known specimens of Tel- anterior half of the prearticular is ventrally masaurus grangeri (see Gilmore, 1943; Bor- covered by the angular bone, and thus, the suk-Bialynicka, 1984). It represents a new anterior part of the prearticular-surangular taxon that is referable to the Platynota on the suture is not exposed in lateral view. The lat- basis of the following character states: pres- 100 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249 ence of plicidentine infolding at the marginal ®rmed for Cherminotus longifrons (see tooth bases; marginal teeth widely spaced above); and as far as this feature is con- with expanded tooth bases; maxillary tooth cerned, the latter two taxa may well occupy row greatly shortened with no more than 13 more basal positions than those mentioned positions, and the tooth row is entirely an- above within the Varanoidea. torbital; vomer strongly elongated approach- ing the level of the posterior end of the tooth Varanoidea, genus and species undetermined row; and palatal shelf of the vomer is narrow Figure 35 (see Gao and Norell, 1998). SPECIMEN: IGM 3/172 (MAE 105/93-42), Within the Platynota, the new taxon is maxillary fragment and associated vertebrae. comparable to Cherminotus longifrons in LOCALITY AND HORIZON: Ukhaa Tolgod, size and number of teeth, but differs from the Nemegt Basin, Mongolian Gobi Desert; Up- latter in having a nonvertical posterior border per Cretaceous Djadokhta Formation. of the splenial and a distinct groove for the REMARKS: The fragmentary maxilla and anterior surangular foramen, and in lacking disarticulated vertebrae (see ®g. 35) are ap- an extra opening of the anterior surangular parently from the same individual, as they foramen below the coronoid process (see were collected in association. The left max- Borsuk-Bialynicka, 1984). It is referable to illary fragment has a fairly complete dorsal the Varanoidea on the basis of a single char- process, which is low and dorsally curved acter state: presence of precondylar constric- towards the midline. It has two incomplete tion of vertebrae; two other characters about teeth preserved, showing widely spaced, the subolfactory process of the frontal and strongly expanded tooth bases with pliciden- entocarotid fossa within the recessus vena tine infolding. The jaw fragment is similar to jugularis are unknown for this taxon. Estesia mongoliensis in size and con®gura- The presence of double lacrimal foramina tion, but the teeth show no indication of a occurs in Varanus and Lanthanotus (Mc- groove although they are incomplete. Dowell and Bogert, 1954; Rieppel, 1980a), Also, the three nearly complete vertebrae and in the fossil taxa Telmasaurus grangeri show that the condyle is well ossi®ed, ex- and Saniwa (Borsuk-Bialynicka, 1984; Gil- panded, and has a strong precondylar con- more, 1928). This morphology was recog- striction. The condylar cup faces ventrally nized as a varanid synapomorphy (e.g., Es- for articulation with a dorsally oriented con- tes, 1983; Pregill et al., 1986; but see also dyle. These are typical varanoid features, in- Gao and Norell, 1998). However, the speci- dicating presence of a large varanoid of a men (IGM 3/171) clearly has a single lacri- size comparable to that of Estesia mongo- mal foramen and a similar condition is con- liensis at Ukhaa Tolgod.

TAXONOMIC DIVERSITY, PHYLOGENETIC SIGNIFICANCE, AND STRATIGRAPHIC DISTRIBUTION OF THE LIZARD ASSEMBLAGE

TAXONOMIC DIVERSITY: The lizard speci- of the total number of lizard specimens ever mens collected from Ukhaa Tolgod and other collected and about half of the total number Gobi localities document an important Late of species known from the Gobi Desert. The Cretaceous lizard assemblage, which shows 30 species are classi®ed in four higher tax- considerable taxonomic diversity. In a pre- onomic groups: Iguania, Gekkota, Scinco- liminary survey of the collection amassed morpha, and Anguimorpha. The Iguania are during the 1993±1997 ®eld seasons, approx- documented by three new and ®ve known imately 1000 specimens represent at least 30 species. This rich fossil record re¯ects an im- species, including seven new species de- portant Late Cretaceous radiation of the scribed in this paper (see table 1; appendix group in the Gobi Desert. The Scincomorpha 1). The collection represents more than half are the most diverse group, represented by as 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 101

Fig. 35. Varanoidea, undetermined genus and species: A, B, IGM 3/172, left maxillary fragment lateral and medial views; C±F, associated vertebrae in dorsal and ventral views. 102 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249

many as 14 species including three new and In terms of taxonomic diversity, lizards 11 previously known species. The Angui- constitute an extremely conspicuous element morpha are nearly as diverse as the Iguania, of the vertebrate faunas of the desert systems while the Gekkota is the least diverse group today (Pianka, 1986). For instance, one of with a single species documented in the as- the desert regions with a large number of semblage. species (the vast interior of Australia) 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 103 was referred to as ``a land of lizards'' (Fin- for a better understanding of character trans- layson, 1943). Many extant lizard clades may formation among lizard groups, and will al- have evolved in response to a desert envi- low us to test the current phylogenetic hy- ronments, as 11 of the 15 recognized extant pothesis through the addition of both char- familial groups occur in these systems (Pian- acters and taxa. For example, the presence of ka, 1986; Mattison, 1989). Among several a forked postfrontal that clasps the fronto- studied areas with sand dune environments, parietal suture has been interpreted as a scler- North American desert sites support from as oglossan synapomorphy (Estes et al., 1988) few as 4 to 10 species, whereas the Kalahari because it is absent in extant iguanians. Sur- Desert in supports 11±17 species. The prisingly, de®nite presence of the forked con- richest lizard fauna today lives in the Great dition in some Late Cretaceous iguanians as Victoria Desert of Australia, where as many described in this paper suggests an alterna- as 40 species have a sympatric distribution tive interpretation: it may well be a primitive (Pianka, 1986). Compared to the desert sys- condition for squamates generally, and is lat- tems today, the Late Cretaceous Gobi Desert er lost in crown-group iguanians. Another probably sustained one of the most taxonom- example concerns the anteromedial process ically diverse lizard faunas yet reported. of the maxilla. Modern acrodontans have Since the 1920s, some 2000 specimens have well-developed processes that meet antero- been collected from the Gobi, and more than medially below the palatal extension of the 60 species have been recognized. Study of premaxillae (Cope, 1864). Estes et al. (1988) these fossil lizards gives important insight interpreted this condition as a potential syn- into the taxonomic diversity of the Late Cre- apomorphy of Acrodonta, although they not- taceous lizard fauna in the Gobi Desert, and ed variation in agamids and its occurrence in thus permits more accurate estimation of the some gekkonids (recognized by Rieppel, phylogenetic diversity (Nixon and Wheeler, 1984). However, new fossils described in this 1992) of the major squamate clades. paper show de®nite occurrences of this mor- PHYLOGENETIC SIGNIFICANCE: The lizard phology in several fossil iguanians (e.g., sample from Ukhaa Tolgod and adjacent lo- Ctenomastax parva, Temujinia ellisoni, calities includes phylogenetically important Phrynosomimus asper) and some scinco- basal taxa of various well-established clades. morphs (e.g., Tchingisaurus multivagus). Ex- For example, the most extensive collection planation of these occurrences requires re- of Carusia intermedia is documented by evaluation of this character state in squamate some 40 exquisitely preserved skulls with evolution. As many of these Late Cretaceous mandibles from this area. A recent study lizards appear to be basal taxa of their related showed that Carusia intermedia is a basal extant clades, incorporation of these fossil member of the Carusioidea, which in turn taxa in a comprehensive analysis will have represent the most basal anguimorph clade important effects on reconstruction of the (Gao and Norell, 1998). Recognition of the phylogenetic history of the major lizard Carusioidea as an anguimorph basal clade is clades. phylogenetically signi®cant, as it helps to re- STRATIGRAPHIC DISTRIBUTION: A survey of solve an Anguidae/Xenosauridae/Varanoidea the known fossil record shows that certain polytomy (see e.g., Estes et al., 1988). Other lizard species occur only in Djadokhta beds, important basal taxa documented in the col- while others only in Barun Goyot beds; there lection include: Gobiderma (basal taxon of are also those species that have a relatively the Monstersauria, see Norell and Gao, long range, occurring in both horizons. To 1997), and Myrmecodaptria (possible basal compile data concerning the stratigraphic taxon of Gekkota, this paper). distribution of lizard taxa in the Gobi series, Current understanding of the phylogeny of we constructed a chart to show the geological the extant lizard clades is primarily based on range of the selected taxa (see table 1). results of the phylogenetic analysis by Estes Sources of data were from various publica- et al. (1988). However, recent discoveries of tions, including Gilmore (1943), Sulimski fossil lizards from Late Cretaceous deposits (1972, 1975, 1984), Borsuk-Bialynicka in the Gobi Desert furnish important material (1984, 1985, 1988), Alifanov (1993a, 1993b, 104 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249

1996), Gao and Hou (1996), Norell et al. scincomorphs that are con®ned to the Dja- (1992), and this paper. It is obvious from this dokhta Formation or its equivalents. On the chart that lizards provide little evidence for other hand, several other scincomorphs are temporally ordering or subdividing Barun only known from the Barun Goyot or youn- Goyot and Djadokhta localities, since 15 of ger horizons. These include: Cherminsaurus the 19 (78.9%) lizard species that occur at kozlowskii, Erdenetesaurus robinsonae, Ma- more than one locality are found in both the crocephalosaurus chulsanensis, Pyramice- Barun Goyot and Djadokhta localities. phalosaurus cherminicus, and Darchansau- IguaniansÐAmong the iguanians, Mimeo- rus estesi. saurus crassus and Isodontosaurus gracilis A large number of scincomorph species appear to be typical ``Djadokhta-type'' of liz- are known from both Djadokhta and Barun ards. Both have been known since the 1940s Goyot horizons: Adamisaurus magnidenta- (Gilmore, 1943), but have never been re- tus, Gobinatus arenosus, Tchingisaurus mul- ported from horizons other than the Dja- tivagus, Eoxanta lacertifrons, Slavoia dar- dokhta Formation. Several other iguanian evskii, and Globaura venusta. Interestingly, species are also restricted to Djadokhta beds. specimens of Slavoia darevskii are quite These include Anchaurosaurus gilmorei, abundant at Ukhaa Tolgod (Djadokhta) and Zapsosaurus sceliphros, and Temujinia elli- Khermeen Tsav (Barun Goyot), but are un- soni. As discussed elsewhere in this paper, known from another Djadokhta-type locality Anchaurosaurus gilmorei from Bayan Man- (Bayan Mandahu) that was extensively sam- dahu and Zapsosaurus sceliphros from Tug- pled. This may be related to the different rugeen Shireh are probably more closely re- type of facies at these localities: both Ukhaa lated to one another than to any other lizard. Tolgod and Khermeen Tsav have deposits The two forms occur in the same horizon that were formed under mesic environments, (Djadokhta), but not at the same locality. The whereas Bayan Mandahu re¯ects an eolian species Polrussia mongoliensis seems to be depositional system (Jerzykiewicz et al., con®ned in the Barun Goyot Formation, 1993; Loope et al., 1998). whereas three others (Ctenomastax parva, AnguimorphsÐOnly a few anguimorphs Priscagama gobiensis, Phrynosomimus as- per) are known from both Djadokhta and Ba- seem to have a distribution con®ned to the run Goyot horizons. Djadokhta beds. These include: Bainguis GekkotansÐAs mentioned elsewhere in parvus, and the two forms (Aiolosaurus or- this paper, the fossil record indicates that the iens and Varanoidea, genus and species un- gekkotans are the least diverse group of liz- determined) described in this paper. Three ards in the Cretaceous Gobi Desert. There are other anguimorphs (Proplatynotia longiro- only two taxa known from the Djadokhta strata, Parviderma inexacta, Saniwides mon- Formation: Gobekko cretacicus from the goliensis) are known only from the Barun Bayn Dzak locality (Borsuk-Bialynicka, Goyot horizon to date. The taxa mentioned 1990), and Myrmecodaptria microphagosa above are relatively poorly known and are from Ukhaa Tolgod (this paper). Another more or less problematic taxonomically. Central Asian record of the group is from the Well-established anguimorph taxa include: deposits exposed at Khoob- Carusia intermedia, Gobiderma pulchrum, ur (Hobur) (Alifanov, 1989b). Estesia mongoliensis, Cherminotus longif- ScincomorphsÐTwo new taxa (Parmeo- rons, Telmasaurus grangeri. All these spe- saurus scutatus and Hymenosaurus clarki) cies are known from both the Djadokhta and described in this paper are among the few Barun Goyot horizons. 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 105

PALEOECOLOGY AND MODE OF SPECIMEN PRESERVATION The general ecosystem of the Late Creta- (contra Jerzykiewicz et al., 1993). Regardless ceous Gobi Desert was compared with the of differing interpretations, we provide here present-day Okavango Oasis, Kalahari De- a brief discussion of the mode of lizard fossil sert in East Africa (Jerzykiewicz, 1998). Al- preservation in relation to the paleoenviron- though the Upper Cretaceous Djadokhta For- ment (facies) at Ukhaa Tolgod. mation deposits were interpreted to be pre- Compared to other fossil localities within dominantly formed in arid or semi-arid, al- the Gobi Desert, the fossils from Ukhaa Tol- luvial to eolian environments (Gradzinski god are characterized by exceptional preser- and Jerzykiewicz, 1974a; Jerzykiewicz et al., vation and concentration. As mentioned 1993; Eberth, 1993), lizard specimens are of- above, all the lizard specimens were collect- ten preserved in association with different fa- ed from ®ne-grained and structureless sand- cies (or microenvironments), as re¯ected by stones, and the surfaces of the bones show different modes of preservation. For exam- essentially no sand abrasion. Not only are ple, specimens from Bayan Mandahu are pre- complete or nearly complete skulls with un- served in association with three different fa- worn teeth commonly found, they often pre- cies (Jerzykiewicz et al., 1993): serve delicate parts (e.g., braincase, semicir- (1) Articulated lizard skeletons were col- cular canals; see ®g. 36C). This type of pres- lected, in association with in situ articulated ervation is indicative of quick burial without dinosaurs, from structureless sandstones, signi®cant ¯uvial transport, and fossilization which have been interpreted as sandstorm in a relatively moist environment with very deposits containing autochthonous faunal low energy water involved in the taphonomic components. process. Such environment is more likely to (2) Surface-worn specimens of isolated occur in a stabilized rather than active dune skulls with mandibles are often preserved in ®eld. caliche nodules, in association with extrafor- Many fossil taxa recorded in the collection mational granules, pebbles, or cobbles. This apparently represent burrowing lizards. type of sediment has been interpreted as al- These include two forms (Phrynosomimus luvial deposits containing allochthonous fau- asper and Slavoia darevskii) that probably nal components. shared the same microenvironment, as the (3) A large number of lizard specimens are specimens of these two taxa are often pre- preserved in calcite-cemented toesets of eo- served in the same kind of loose sand de- lian dune deposits. The nature of this type of posits. Phrynosomimus asper is an acrodon- deposit is not well understood, but could re- tan iguanian that in skull morphology shows ¯ect a habitat preference for a moist substrate a striking similarity to the North American or diagenetic control on the preservation of ``'' (Phrynosoma). Although the fossils (Jerzykiewicz et al., 1993). having an acrodont dentition, the marginal A similar three-facies setting has been rec- teeth of this lizard are reduced in size par- ognized at Ukhaa Tolgod, where the redbeds alleling those of the ``horned lizard,'' which are inferred in association with two eolian specialize on a diet of ants in desert environ- facies (Facies E-1-2 of Loope et al., 1998) ments. Slavoia darevskii (scincomorph), and one alluvial fan facies (Facies F of Loo- commonly known from Khulsan and Kher- pe et al., 1998). In contrast to the Bayan meen Tsav of the Barun Goyot Formation Mandahu locality, however, the alluvial fan (Sulimski, 1984), is now known from Ukhaa (Facies F, structureless sandstones lacking Tolgod. It shows convergent similarities to oriented concretions) is the only facies con- southern African acontine skinks (see discus- taining lizard and other vertebrate fossils at sion above), which spend a large proportion Ukhaa Tolgod (Loope et al., 1998). Loope et of their lives below ground, feeding on al. (1998) interpreted the structureless sand- and other soft-bodied small inverte- stones accompanying in situ burial of brates (Mattison, 1989). skeletons as likely to occur on sand fans dur- Known from both Djadokhta (Bayn Dzak ing rain storms within a stabilized dune ®eld and Ukhaa Tolgod) and Barun Goyot (Kher- 106 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249

meen Tsav and Khulsan) localities, Globaura venusta is obviously another lizard that was highly adapted to a burrowing life-style. It has a pointed snout and an enlarged brain- case exposed posterior to the parietal (Riep- pel, 1981). The skull morphology, in keeping with its preservation in poorly cemented sandstone, suggests that the species may rep- resent a Late Cretaceous ``ecological equiv- alent'' of extant sand®sh in North African, Middle Eastern, and North American deserts (e.g., Mattison, 1989). Exceptional preservation of virtually com- plete and undistorted articulated lizard skel- etons at Ukhaa Tolgod deserves special at- tention. Some of these skeletons apparently represent burrowing lizards that died under- ground and are preserved in burrows. For ex- ample, some specimens of Parmeosaurus scutatus are preserved in a unique curled body position, with the head hidden under- neath the tail (®g. 24). These skeletons are preserved in sandstone concretion blocks, which are better cemented than, and are sep- arated from, the surrounding sediment. This interpretation (skeletons preserved in bur- rows) is supported by the skull morphology of this lizard, as the pointed snout and en- larged braincase exposed posterior to the pa- rietal are obviously related to burrowing (see Rieppel, 1981). Mesozoic examples of lizard skeletons preserved in burrows are rarely known. The lizard fossils mentioned above may represent one of the earliest known ex- amples of lizard skeletons preserved in bur- rows. Another type of preservation of virtually complete skeletons is depicted by an iguani- an specimen (®g. 37). The skeleton is re- markably complete with only parts of the right limbs missing. The completeness of the Fig. 36. Exceptional preservation of lizard skeleton gives clear indication of quick buri- specimens at Ukhaa Tolgod: A, SEM photograph al during rapid deposition, and the ``strug- of unworn dentary teeth of IGM 3/50 (Carusia gling'' position of the skeleton preserved in intermedia), ϫ20; B, higher magni®cation of ®ne-grained sandstones seems to indicate a three posterior teeth in lingual view, ϫ50; C, un- muddy sand fan formed during a major rain- distorted braincase of a possible iguanian, arrows storm (see Loope et al., 1998). pointing to lateral semicircular canal. Besides different modes of specimen pres- ervation, another line of evidence for pa- leoenvironmental inference comes from den- tition of lizards. As evidenced from tooth morphology (crown pattern, in particular), the lizards from Ukhaa Tolgod are predomi- 2000 GAO AND NORELL: LATE CRETACEOUS LIZARDS FROM MONGOLIA 107

Fig. 37. Virtually complete lizard skeleton from Ukhaa Tolgod, dorsal view (courtesy of Amy Da- vidson). nantly predatory (carnivorous and insectivo- zation can be made based on different types rous), like those from the Bayan Mandahu of dentition (Greene, 1982): those with tri- locality of Inner Mongolia (see Gao and cuspid crowns in different higher taxonomic Hou, 1996). True are extremely groups (Iguania and Scincomorpha) are high- rare, in contrast to other localities such as ly adapted for crushing soft- to hard-shelled Khermeen Tsav and Khulsan, where large (e.g., Hotton, 1955), whereas others herbivores (e.g., Macrocephalosaurus, Cher- with peglike teeth are highly adapted for a minsaurus) with polycuspid teeth are com- myrmecophagous diet. These feeding adap- mon (see Sulimski, 1975). Since Ukhaa Tol- tations provide an important source of infor- god has been extensively sampled for years, mation for the ecological characterization of we interpret the paucity of true herbivorous lizard species, and for understanding the pa- lizards as a natural phenomenon of the as- leoenvironment in which these species inhab- semblage, not a taphonomic artifact. Among ited. the , further ecological categori-

CONCLUSIONS A taxonomically diverse lizard assemblage groups (Iguania, Gekkota, Scincomorpha, from Ukhaa Tolgod and adjacent localities and Anguimorpha). Iguanians are represent- includes at least 30 species in four higher ed by eight species, and are relatively abun- 108 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 249 dant in terms of number of taxa and individ- mens are often preserved in association with uals. The Scincomorpha are the most diverse different facies that re¯ect different types of group, represented by as many as 14 species. microenvironments in the Gobi. Many taxa The Anguimorpha are nearly as diverse as are obviously desert dwellers, showing ad- the Iguania, whereas the Gekkota are the aptations to a burrowing life-style as inter- least diverse group with a single species doc- preted from their cranial morphology and umented in the assemblage. possible analogies of extant species. Some Several new taxa are named and described specimens apparently represent lizards that based on well-preserved skulls or skeletons. died underground and were preserved in bur- Recognition of these new taxa provides im- rows. Virtually complete skeletons preserved portant insights into the taxonomic diversity in poorly cemented ®ne-grained sandstones of the lizard assemblage and the phylogenet- at Ukhaa Tolgod seems to re¯ect quick burial ic diversity of the relevant lizard clades. in muddy sand fans that formed during major These include phylogenetically signi®cant rainstorms. As evidenced from tooth mor- basal taxa of various well-established clades, phology, lizards from Ukhaa Tolgod are pre- and hence, description of the morphological dominantly predatory, whereas true herbi- details of these taxa lay the foundation for vores are extremely rare. Further study of the future comprehensive cladistic analyses of feeding adaptations of these lizards is signif- the relevant lizard groups. icant for understanding the paleoenviron- The paleoecological signi®cance of these mental details of the Late Cretaceous Gobi lizards cannot be overlooked. Lizard speci- Desert.

ACKNOWLEDGMENTS This paper is based on signi®cant ®eld dis- and photographed the complete skeleton in coveries from the Mongolian Gobi Desert by ®gure 37 (all other specimens were prepared members of the Mongolian Academy of Sci- by the ®rst author). Adrine MacDonald ences±American Museum of Natural History helped in preparation of some drawings (®g- joint expeditions of the 1990s. We thank all ures 7, 14, and 19). We thank the two anon- those involved. We thank Darrel Frost and ymous reviewers for their helpful comments. Linda Ford (Department of , The research was supported by the Frick American Museum of Natural History) for Laboratory Endowment, the Department of providing skeletal specimens of the extant Vertebrate Paleontology, American Museum of Natural History, the National Science species for comparison, and Demberelyin Foundation (NSF DEB 9300770), the IREX Dashzeveg for translation of literature in Foundation for International Research, the Russian. Extensive discussion with Susan E. National Geographic Society, the Philip Mc- Evans (University College London) helped Kenna Foundation, and Richard, Lynette and to clarify some taxonomic uncertainties. We Byron Jaffe. Gao's work was supported by a thank Mick Ellison for skillful preparation of Frick Research Fellowship of the American photographs and drawings. IGM 3/15 and 3/ Museum of Natural History and by the Na- 16 were prepared by M. Fox, IGM 3/53 and tional Science Foundation (NSF DEB- 3/61 by Amy Davidson, who also prepared 9806811).

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