AMERICAN MUSEUM Novitates PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, N.Y. 10024 Number 3045, 24 pp., 13 figures, 1 table July 27, 1992 Estesia mongoliensis, a New Fossil Varanoid from the Late Cretaceous Barun Goyot Formation of Mongolia1 MARK A. NORELL,2 MALCOLM C. McKENNA,3 AND MICHAEL J. NOVACEK3 ABSTRACT A new lizard from the Late Cretaceous Barun minotus and Saniwa. Although the phylogenetic Goyot Formation was collected during the 1990 relationships among these taxa are uncertain, pre- joint Mongolian American paleontological expe- liminary analysis suggests that the new taxon is dition to the Gobi Desert, Mongolia. This lizard the sister group to Lanthanotus and Varanus. Fur- is referable to a clade containing the extant genera ther, it displays the unusual feature oflongitudinal Lanthanotus, Heloderma, and Varanus, as well as grooves on the teeth, identical to the grooves used several poorly known extinct taxa including Cher- for venom conduction in Heloderma. INTRODUCTION One of the great Mesozoic and Tertiary worowska and Dovchin, 1968). Among these fossil-producing regions in the world is the are Cretaceous mammals and exquisitely Gobi Desert ofMongolia. Since their discov- preserved dinosaurs. Often overlooked, re- ery by field parties ofthe American Museum mains of lizards are among the most numer- in 1923, the Mesozoic beds from this region ous fossils encountered at some localities. have produced spectacular skeletons offossil Mongolian lizard fossils have been de- vertebrates (see Andrews, 1932; Kielan-Ja- scribed by Gilmore (1943) (from specimens ' This is contribution no. 1 of the Mongolian-American Museum Paleontological Project. 2 Assistant Curator, Department of Vertebrate Paleontology, American Museum of Natural History. 3 Curator, Department of Vertebrate Paleontology, American Museum of Natural History. Copyright © American Museum of Natural History 1992 ISSN 0003-0082 / Price $3.80 2 AMERICAN MUSEUM NOVITATES NO. 3045 Fig. 1. The type skull of Estesia mongoliensis. collected by the American Museum Central comparative description of this new taxon Asiatic expeditions) and Borsuk-Bialynicka and place it in a phylogenetic context. Com- (1984) and Sulimski (1972, 1975, 1978) (from ments regarding its explicit phylogenetic re- specimens collected by the Polish-Mongolian lationships are preliminary until a detailed expeditions). Here, we describe a new fossil reanalysis of the relationships among living lizard collected in June 1990, near Khulsan and fossil anguimorphs is accomplished. In in the Barun Goyot Formation by a field party the following discussion, nomenclatural ter- from the Mongolian Academy ofSciences and minology follows Pregill et al. (1986), where the American Museum of Natural History the varanoids include descendants ofthe last (fig. 1). This specimen, a nearly complete common ancestor of Heloderma, Lanthan- skull, displays features that may aid in de- otus, and Varanus, and Varanidae is restrict- ciphering the relationships among angui- ed to the descendants of the last common morph lizards. ancestor of Lanthanotus and Varanus. The Such complete specimens of fossil lizards morphological terminology follows Oelrich are generally rare. Where they exist, phylo- (1956) and Mertens (1942). genetic study is often hampered by a lack of detailed knowledge of extant taxa, making both determination ofcharacter polarity and INSTITUTIONAL ABBREVIATIONS the choice of appropriate outgroup taxa dif- AMNH American Museum of Natural His- ficult. Among lizards phylogenetically affili- tory ated with the taxon described herein (the Va- RE Collection of Richard Etheridge ranoidea), significant progress in resolving MAN Collection of Mark Norell relationships has been accomplished (Riep- MAS Mongolian Academy of Sciences pel, 1980; Gauthier, 1982; and Pregill et al., 1986). Nonetheless, much more work, in- LOCALITY, GEOLOGIC SETTING, AND cluding development of a phylogeny within HISTORICAL BACKGROUND the Varanidae, a detailed analysis ofSaniwa, and a comprehensive review of "necrosau- In 1990, after an absence ofnearly 60 years, rids" is needed. the American Museum of Natural History Our purpose is to provide a diagnosis and resumed exploration in outer Mongolia 1992 NORELL ET AL.: ESTESIA MONGOLIENSIS 3 Mongolian People's Republic Expedition Routes Mongolian - American Roy Chapman Andrews - - - - Mongolian- Polish. Fig. 2. Map of Mongolia, showing routes of American Museum Central Asiatic Expedition, the Polish-Mongolian Expedition, and the Mongolian-American Museum Expedition of 1990. (Mongolian People's Republic until 1991; complete, but badly weathered ankylosaurid now simply Mongolia), in collaboration with skeleton, and several skulls of small lizards. the Mongolian Academy of Sciences. A re- The specimen was collected in the Barun connaissance of south-central Mongolia was Goyot Formation (Gradzinski and Jerzykie- undertaken in the early summer of 1990 (fig. wicz, 1972; Efremov, 1950, 1954, 1955). Ex- 2). During this reconnaissance, the field party posures at the locality are orange pink to light composed of Dr. Demberelyin Dashzeveg of brown, cross bedded and poorly indurated the Mongolian Academy ofSciences, and Mal- sands, with occasional small pebbles. These colm McKenna, Mark Norell, and Michael beds have been considered Late Cretaceous, Novacek of the American Museum of Nat- middle Campanian in age, based on multi- ural History visited the locality of Khulsan, tuberculates (Kielan-Jaworowska, 1974). explored in 1965 by the Polish-Mongolian "Comparative studies of dinosaurs and Expeditions, although fossils were not found mammals" (Gradzinski et al., 1977) suggest there until 1970 (fig. 3). The Khulsan locality that the Barun Goyot Formation is younger yielded a well-preserved skull and mandibles than the Djadokhta Formation at the Flam- and part of a front leg of a large varanoid ing Cliffs locality (Berkey in Granger and lizard in addition to specimens of other liz- Gregory, 1923). Lillegraven and McKenna ards and dinosaurs. The varanoid specimen (1986), however, argued that "the Djadokhta lay in a steep cliff face about 3 km down- and Barun Goyot formations are approxi- stream from the 1971 Polish-Mongolian Ex- mately equivalent in age, respectively, to the pedition's Khulsan camp (Gradzinski and older and younger parts of the North Amer- Jerzykiewicz, 1972). Also recovered at this ican Judithian." These authors stress that de- site were associations ofdinosaur eggs, a skel- termination ofabsolute ages and faunal stages eton of Protoceratops, the skull of a nearly is tenuous. Correlation based on higher taxa 4 AMERICAN MUSEUM NOVITATES NO. 3045 I 11/, t// ,,,A=_ * // 1'' 0 1km Fig. 3. Map ofthe general region of Khulsan showing the locality where the specimen was collected. Modified from Gradzinski and Jerzykiewicz (1972). 1992 NORELL ET AL.: ESTESIA MONGOLIENSIS 5 of dinosaurs and mammals is difficult, no from the border of the suborbital fenestra radiometric or magnetostratigraphic evi- (Pregill et al., 1986). Can be differentiated dence is available, and the beds do not in- from all other varanoids by the following tertongue with any known fossiliferous ma- combination of derived characters: venom rine sediments (Lillegraven and McKenna, grooves on the teeth, and a lack of cranial 1986). osteoderms. Estesia mongoliensis is unique among squamates in possessing an extensive SYSTEMATIC PALEONTOLOGY convex surface medial to the posterior ridge on the posterior surface of the quadrate. REPTILIA COMPARATIVE DESCRIPTION OF HOLOTYPE: SAURIA The skull is a well-preserved cranium of an adult individual. There is no trace of free or LEPIDOSAURIA fused osteoderms accompanying the speci- SCLEROGLOSSA men. The roof of the skull, especially the pa- rietal and the frontals, may have been sculp- ANGUIMORPHA tured, or the crenulated surface may be an VARANOIDEA effect of weathering. The lateral surfaces of the maxillae and the dentaries are smooth as Estesia mongoliensis, new taxon4 in Varanus. Figures 4-7 The right side of the skull is badly weath- HOLOTYPE: M 3/14; a skull and mandibles. ered and only a few elements remain. The ETYMOLOGY: Estes (proper name), and posterior region (i.e., braincase) is crushed; mongoliensis, geographic location, after however, the left side ofthe skull and the left Richard Estes in honor of his timeless con- mandible are nearly complete. Lateral sur- tributions to the study of fossil lizards. faces of the skull and dentaries are smooth, LOCALITY OF HOLOTYPE: Lizard Hill, Khul- whereas the skull roof is covered with fine san. South Gobi Aimak, Mongolia. striations, somewhat like those found in large 43029'19"N, 101°08'44"E (fig. 1). 4741' MSL. adult Varanus. The occipital region ofEstesia DATE COLLECTED: June 1990, by M. C. Mc- mongoliensis is crushed and the fragmentary Kenna, M. A. Norell, and M. J. Novacek occipital condyle has been rotated into the (AMNH), and D. Dashzeveg (MAS). braincase. DIAGNOSIS OF NEW TAXON: Referable to the Varanoidea on the basis of the following OPENINGS OF THE SKULL derived characters: nasal and maxillary bones Large, protracted nares are characteristic with or no contact, little large subolfactory ofEstesia mongoliensis and other varanoids. processes of the frontal, a lack dental re- of The nares reach posteriorly almost to the an- sorption pits, sharply pointed plicidentine terior margin of the orbits. Reminiscent of teeth, a long vomer with narrow palatal the Varanidae is the large