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Some Peculiarties of the Cretaceous and Palaeogene Lizard Faunas of the Mongolian People's Republic

Some Peculiarties of the Cretaceous and Palaeogene Lizard Faunas of the Mongolian People's Republic

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Some peculiarities of the and Palaeogene faunas of the Mongolian People's Republic

Article · January 1993

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Vladimir Alifanov Russian Academy of Sciences

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Vladimir Alifanov Some Peculiarties of the Cretaceous and Palaeogene Lizard Faunas of the Mongolian People's Republic

Author's address: Vladimir Alifano, Moscow Paleontological Institute of Academy of Sciences, 123 Profsoyuznaja, Moscow 117 868; Russia.

Zusammenfassung In der Kreidezeit existierten in Zentralasien vier heute ausgestorbene und 10 rezente Echsenfamilien. Das bedeutendste Ereignis der Oberkreide ist das Erscheinen der , , Paravanidae, und . Gegen Ende der Kreidezeit wurde die Zahl der Familien in der Mongolei auf drei reduziert. Varanidae und Agamidae waren die dominanten Familien im Paläogen. Im mittleren Eozän hatten die Varanidae endgültig die Necrosauridae verdrängt. Zu dieser Zeit erschienen die frühesten Vertreter der Gattung Varanus. Innerhalb der Agamidae des Paläogens gab es Gattungen die Isodontosaurus, Uromastyx oder Leilepis ähnelten. Eine neue Unterfamile der Agamidae - Isodontosaurinae - wird aufgestellt. Nach ihrem oberkretazischen Verschwinden breiteten sich die und Agamidae im Eozän erneut in Zentralasien aus; eine Neueinwanderung der aus Europa fand im unteren Oligozän statt.

Abstract Four extinct and ten recent lizard families existed in Central Asia during the Cretaceous. The main feature of the Upper Cretaceous fauna is the appearance of Agamidae, Varanidae, Paravaranidae, Iguanidae, Teiidae and Anguidae. The number of families was reduced to three by the end of the Cretaceous of Mongolia. The Varanidae and Agamidae only were the dominant families in the Palaeogene. The Varanidae forced out Necrosauridae finally by the Middle . By that time the earliest representatives of Varanus appeared. There are Isodontosaurus-like, Uromastyx-like and Leiolepis-like genera amongst the Palaeogene Agamidae. A new subfamily of Agamidae - Isodontosaurinae is erected. After the Upper Cretaceous extinction the Iguanidae and Anguidae spread in the Eocene of Central Asia again; a new invasion of the Lacertidae from Europe happened in the Lower Oligocene.

The material of the fossil from Mongolia was collected by the Joint Soviet-Mongolian Pale- Gekkonidae GRAY 1825 ontological Expedition in the South and East of the Hoburogekko ALIFANOV 1989 Gobi Desert during the last 22 years. The numerous lizard specimens originate from eight Cretaceous ESTES 1983 and five Palaeogene localities. ?Xantusidae BAIRD 1859 The bone material was extracted by washing of Acontiidae GRAY 1845 rock and direct collectioning. Slavoia SULIMSKI 1984 The present report is preliminary and represents the first attempt of the survey of the Mongolian ? COPE 1886 Lower Cretaceous and Palaeogene lizard faunas. Dorsetisauridae HOFFSTETTER 1967 HOFFSTETTER 1967 The Lower and Upper Cretaceous ?Necrosauridae HOFFSTETTER 1943 The earliest fauna of the Mongolian fossil lizards is Hodzhaculia NESSOV 1985 usually dated as Lower Cretaceous (Aptian-Albian) The presence of the Dorsetisauridae and Para- (KALANDADZE & KURZANOV 1974). This unique fauna macellodidae in the composition of the Hobur's fills in the gap between the faunas of the European fauna drew it together with the Upper ones Upper Jurassic and the Upper Cretaceous of Cen- from West Europe (HOFFSTETTER 1967, ESTES 1983) tral Asia and North America. The numerous mac- and North America (PROTHERO & ESTES 1980). This erated material comes from the only locality fact demonstrates the existence of the Lawrasian "Hobur". stage for the lizard faunas of the Northern conti- By the present time the representatives of all nents. lizard infraorder were determined: The Upper Cretaceous localities containing liz- Iguania ard remains are represented by the three Formati- BORSUK-BIALYNICKA & MOODY 1984 ons Djadochta (Bain-Dzak, Dzamyn-Hond, Tug- (sensu ALIFANOV 1989) rikiyn-Sheere), Barun-Goyot (Khemeen-Tsav, 10 Vladimir Alifanov

mx

Pf mx mx Pt

Fig. 1: Isodontosaurus gracilis GILMOR 1943: specimen MgR/II-39, Upper Cretaceous (), Bain- Dzak locality. A: Skull, dorsal view. B: Mandible, labial view. C: Mandible, lingual view. ang - angular, с - coronoid, d - dentary, ept - epipterygoid, fr - frontal, mx - maxilla, pf - prefrontal, pt - ptery- goid, spl - splenial.

Hulsan) and Nemegt (Bugeen-Tsav, Guriliyn-Tsav), These families precede the Varanidae and Agamidae which are dated by BARSBOLD 1982 as Santonian- morphologically and ecologically. Lower Campanian (Djadochta and Barun-Goyot The main feature of the Upper Cretaceous fauna Formations) and Upper Campanian-Lower Maas- is the appearance of new lizard families: trichtian (Nemegt Formation). Iguanidae OPPEL 1811 sensu lato By the Upper Cretaceous the Dorsetisauridae Polrussia BORSUK-BIALYNICKA & ALIFANOV 1991 only disappear from the paleontological record of BORSUK-BIALYNICKA & ALIFANOV 1991 Mongolia. Agamidae SPIX 1825 The earlier existing Asiatic families are repre- Isodontosaurus GILMOR 1943 (Fig. 1) sented by the following genera: Teiidae GRAY 1827 Priscagamidae Macrocephalosaurus GILMOR 1943 Priscagama BORUSK-BIALYNICKA 1984 Conicodontosaurus GILMOR 1943 Pleurodontagama BORSUK-BIALYNICKA 1984 Adamisaurus SULIMSKI 1972 GILMOR 1943 Erdenetosaurus SULIMSKI 1975 Flaviagama ALIFANOV 1989 Cherminsaurus SULIMSKI 1975 Gekkonidae Darchansaurus SULIMSKI 1975 Gobekko BORSUK-BIALYNICKA 1990 Mongolochamops ALIFANOV 1988 Paramacellodidae Piramicephalosaurus ALIFANOV 1988 a few undescribed genera Lacertidae GRAY 1825 Xantusiidae Anguidae GRAY 1825 Eoxanta BORSUK-BIALYNICKA 1988 Bainguis BORSUK-BIALYNICKA 1984 (sensu BORSUK- Acontiidae BIALYNICKA 1991) Slavoia SULIMSKI 1984 Varanidae GRAY 1827 Xenosauridae Telmasaurus GILMOR 1943 Carussia BORSUK-BIALYNICKA 1987 Saniwides BORSUK-BIALYNICKA 1984 Shinisauroid.es BORSUK-BIALYNICKA 1985 Cherminotus BORSUK-BIALYNICKA 1984 (Fig. 2) Globaura BORSUK-BIALYNICKA 1988 sp. (Fig. 3) Necrosauridae Paravaranidae Proplatinotia BORSUK-BIALYNICKA 1984 Paravaranus BORSUK-BIALYNICKA 1984 Parviderma BORSUK-BIALYNICKA 1984 These new families might be subdivided into Gobiderma BORSUK-BIALYNICKA 1984 three groups. Taking into consideration the undescribed gen- The first group is made up from Varanidae and era, the Necrosauridae and Priscagamidae are the Agamidae, which are Asian by origin and had a most diverse among the above mentioned families. powerful generic diversity in Asia only. Some Peculiarties of the Cretaceous and Palaegene Lizard Faunas of the Mongolian People's Republic 11

pmx and are known from the Upper Paleocene, but one could assume their distribution mx in the Upper Cretaceous. More likely, the named groups came to Asia from North America. If right, Hobur's fauna was formed before the connection of Asia to North America. The distribution of the second group both in Asia and South America might probably occur only due to its North American origin as well as the earlier interamerican connection, than that of North America to Asia. This might explain the absence of the Asian Necrosauridae, Varanidae, Xenosauri- dae and Agamidae in the South America. The third group includes the Paravaranidae and Lacertidae. To my opinion, the problematic mono- typical Paravaranidae display a lot of similiarities with the mosasauroid known from the Upper Jurassic-Lower Cretaceous of Europe. If true, Paravaranidae might be regarded as Jurassic relic in Mongolian Upper Cretaceous. Lacertidae, which might have a hidden Mesozoic distribution in Lawrasian time, are a more problematic family. 5 mm In the terminal Cretaceous Nemegt Formation Fig. 2: Cherminotus longifrons BORSUK-BIALYNICKA the quantity of the lizard families was reduced to 3 1984; specimen PIN 3142/323; Upper Cretaceous (Varanidae, Necrosauridae, Teiidae). The absence (Barun-Goyot Formation ), Khermeen-Tsav locality, of Agamidae in Nemegt deposits and Varanidae in ept - epiterygoid, fr - frontal, j - jugal, 1 - lateral, the Upper Paleocene ones indicates to some local mx - maxilla, n - nasal, p - parietal, pfr - prefrontal, features of the lizard extinction. pmx - premaxilla, po - postorbiatal, pofr - postfron- tal, pt - pterygoid. The Upper Paleocene (Table 1) The impoverishment of the lizard fauna kept on The second group includes modern Iguanidae going in the Cenozoic. By the Upper Paleocene the sensu lato, Teiidae and Anguidae as well as Necrosauridae (Necrosaurus sp.) and Agamidae only and Amphisbaenia. All these are united are recorded. The latter are represented by the by modern distribution in South America. The undescribed Leiolepis-like and Isodontosaurus-like earliest fossil Teiidae, Anguidae and Ophidia are genera. known from the Upper Cretaceous of North Isodontosaurus-like forms have got no fang-like America. The earliest North American Iguanidae teth and pronounced hatchling teeth. The tooth

Fig. 3: Saniwa sp., specimen PIN 3142/322 (trunk vertebra), Upper Cretaceous (Barun-Goyot Formation), Khermeen-Tsav locality. A: Ventral view. B: Dorsal view. 12 Vladimir Alifanov

Upper Middle Lower Palaeocene Eocene Oligocene Iguania Iguanidae OPPEL 1811 sensu lato - Arretosaurus sp. Arretosaurus sp. Agamidae SPIX 1825 Isodontosaurinae subfam. nov. 2 undescribed 6 undescribed genera - genera Agaminae SPIX 1825 Uromasticini THEOBALD 1868 - Pseudotinosaurus undescribed n. comb. ALIFANOV 1991 and 3 undescribed genera Leiolepini FITZINGER 1843 undescribed genus undescribed genus - n. comb. Anguimorpha Necrosauridae HOFFSTETTER 1943 Necrosaurus sp. - - Varanidae GRAY 1827 Saniwa sp. 1 and 2, Varanus sp. 3 Varanus sp. 1 and sp. 2 Anguidae GRAY 1825 - - Placosaurus sp. Scincomorpha Lacertidae GRAY 1825 - - Lacerta sp. Localities Tsagan-Hushu Tsagan-Hushu, Khaichin- Hoer-Dzan Ula 2, Khaichin-Ula 3 Ergyliyn-Dzo

Table 1: List of the Mongolian Palaeogene lizards of Mongolia. rows of this agamid genera are hyperpleurodont, lian iguanid lizard look like the Lower Oligocene pleurodont or acrodont. The teeth possess expressed Arretosaurus from China (GILMORE 1943) and recent or unclear tricuspid crowns. All teeth are not sepa- Phrynosoma which possess the subpleurodont rated from the subdental shelf. These characters mandibular teeth, the split-like Meckelian opening make it possible to erect a new subfamily of Agami- and the vertical premaxilla-maxillary contact. dae, Isodontosaurinae nov. with Isodontosaurus GIL- The presence of the Middle Eocene Agamidae, MORE 1943 (Fig. 1) as a type genus. The agamid Iguanidae and Varanidae in Asia, North America and relationship is proved with the presence of the long Europe (ESTES 1983) confirms the existence of a fauni- angular, the coronoid and supraanuglar processes stical connection between Asia and Europe across of the dentary as well as the reduction of the splenial North America (BADAMGARAV & RESHETOV 1985). without the formation of the closed Meckelian ca- nal. The Lower Oligocene (Table 1) Five families of lizards are known in the Mongolian The Middle Eocene (Table 1) Lower Oligocene. The Varanidae are represented The Middle Eocene fauna already includes 3 fami- by a large species of Varanus. The Agamidae are lies: Varanidae, Agamidae, Iguanidae: represented by a new Uromastyx-like genus. The There is no evidence of the presence of Necro- Iguanidae are represented by the fragmentary spe- sauridae. Varanidae are represented by the small cies of Arretosaurus. The Mongolian specimen looks and large species of Saniwa and the earliest repre- like specimen A.M. 6708, described by GILMOR (1943) sentatives of Varanus (Fig. 4). The largest represen- from China (Inner Mongolia). tative of Saniwa reached nearly 2 metres in length. The remains of the Palaeogene Iguanidae from At the Middle Eocene the Mongolian Varanidae Mongolia are found in the same taphocoenosis as probably forced out the archaic Necrosauridae. the different Agamidae. The competitive forcing The Agamidae are very diverse. There are nu- out of the Iguanidae and archaic Isodontosaurinae merous genera close to Uromastyx and Leiolepis in Asia probably resulted from the explosive spread- within Agaminae and numerous genera of Isodonto- ing of Agamini in the Upper Oligocene-Miocene. saurinae. The largest representative of the latter Agamini are absent in the Palaeogene deposits of subfamily has the same the body size as the largest Mongolia but there are some in the Upper Paleocene Iguanidae. of China {"Agama" sinensis) (Hou 1974). Iguanidae appear after the Upper Cretaceous A new appearance of the Lacertidae occured extinction again. Some feature of the small Mongo- after the Upper Cretaceous extinction. This family, Some Peculiarties of the Cretaceous and Palaegene Lizard Faunas of the Mongolian People's Republic 13

unknown from North America, had a chance to move to Asia from Europe only. Besides the Mongolian Lower Oligocene, the Cenozoic Aguidae are known from the Upper Eo- cene of China (Inner Mongolia) (GILMORE, 1943); there- fore their North American invasion is proposed. Conclusions Known from the extensive time interval, the Mon- golian lizard faunas give the unique possibility to research the lizard history on a single continent. It is undifficult to sum up, that the modern lizard diversity was formed in the Upper Cretaceous. After that, the peculiarties of the Asian lizard fauna were forming in general during the Upper Creta- ceous and Palaeogene.

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