TAXONOMIC COMPOSITION AND SYSTEMATICS OF LATE CRETACEOUS LIZARD ASSEMBLAGES FROM UKHAA TOLGOD AND ADJACENT LOCALITIES, MONGOLIAN GOBI DESERT GAO KEQIN Frick Research Fellow, Division of Paleontology 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 q American Museum of Natural History 2000 ISSN 0003-0090 CONTENTS Abstract ....................................................................... 4 Introduction .................................................................... 4 Geological Setting .............................................................. 5 Systematic Paleontology ........................................................ 11 Squamata Oppel, 1811 ....................................................... 11 Iguania Cope, 1864 .......................................................... 11 Iguanidae (sensu lato: nonacrodontan iguanians) ............................... 11 Ctenomastax parva, new genus and species ................................ 11 Temujinia ellisoni, new genus and species .................................. 18 Zapsosaurus sceliphros, new genus and species ............................. 25 Polrussia mongoliensis Borsuk-Bialynicka and Alifanov, 1991 ................ 31 Acrodonta Cope, 1864 ..................................................... 32 Mimeosaurus 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 Gekkota Cuvier, 1817 ........................................................ 46 Family Incertae sedis ...................................................... 47 Myrmecodaptria microphagosa, new genus and species ...................... 47 Scincomorpha Camp, 1923 ................................................... 52 Teiidae 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 Anguimorpha FuÈrbringer, 1900 ................................................ 90 Carusioidea Gao and Norell, 1998 ........................................... 90 Carusiidae Borsuk-Bialynicka, 1987 ......................................... 90 Carusia intermedia Borsuk-Bialynicka, 1985 ............................... 90 Platynota Camp, 1923 ...................................................... 92 Monstersauria Norell and Gao, 1997 ......................................... 92 Gobiderma pulchrum Borsuk-Bialynicka, 1984 ............................. 93 Estesia mongoliensis Norell et al., 1992 .................................... 94 Varanoidea 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: LATE CRETACEOUS LIZARDS 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 basal members of several major anguimorph clades. The paleoecological signi®cance of these lizards cannot be overlooked. According to tooth morphology, most lizards are predatory in terms of habit, while true herbivorous species are rare. Most specimens are preserved as skulls articulated with mandibles, but virtually complete skeletons in situ are quite common. Delicate parts of the skull, 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 years, the Mongolian beds are Djadokhta equivalents. The dino- Academy of Science±American Museum of saur and mammal assemblages show both Natural History Expeditions made extraor- Djadokhta and Barun Goyot af®nities (No- dinary fossil 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-Campanian, 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 vertebrate sides signi®cant mammal and dinosaur 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