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Protoceratops Andrewsi and Velociraptor Mongoliensis and Similar Dinosaur Eggs

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Protoceratops Andrewsi and Velociraptor Mongoliensis and Similar Dinosaur Eggs ACT A PAL A EON T 0 LOG ICA POLONICA Vol. 23 1978 No 2 ZOFIA KIELAN-JAWOROWSKA AND DEMBERLYIN DASHZEVEG NEW LATE CRETACEOUS MAMMAL LOCALITY IN MONGOLIA AND A DESCRIPTION OF A NEW MULTITUBERCULATE Abstract. - A multituberculate Tugrigbaatar saichanensis gen. n., sp. n., assigned to the Eucosmodontidae is described on the basis of a skull and fragments of postcranial skeleton. It resembles a eucosmodontid from the Djadokhta Formation, Kryptobaatar dashzevegi, with which it is compared in detail. A multituberculate humerus is reconstructed. The Toogreeg beds cropping out at the locality of Toogreeg in the Gobi Desert (ca. 30 km WNW of Bayn Dzak) yield late Cretaceous mammals. The age of the beds is tentatively estimated as approximately equivalent to that of the Djadokhta Formation (?late Santonian and/or ?early Campanian). INTRODUCTION The fossil locality of Toogreeg (Toogreegeen Shireh), situated some 30 km WNW of Bayn Dzak in the Gobi Desert, was discovered in 1961 by Dr. R. Barsbold and the second author (see Dashzeveg 1963). In 1969, 1970, 1975 and 1976 this locality was explored by the Soviet-Mongolian Expeditions (Kurzanov 1972, Kramarenko 1974, Tverdochlebov and Tsybin 1974). The Polish-Mongolian Palaeontological Expedition worked there for one week in 1970 (Kielan-Jaworowska and Barsbold 1972, Gradziilski and Jerzykiewicz 1972, Maryailska and Osm61ska 1975, Gradziilski et al. 1977). The sandstone cropping out at Toogreeg is different lithologically from that of the Djadokhta Formation at Bayn DZak, but yields the same dinosaurian species: Protoceratops andrewsi and Velociraptor mongoliensis and similar dinosaur eggs. In 1974 the second author found the skull of a multituberculate associated with fragments of its postcranial skeleton, in the eastern part of the outcrops at Toogreeg, in concretions of light-grey sandstone. The specimen is described in the present paper as Tugrigbaatar saichanensis gen. n., sp. n., assigned to the Eucosmodontidae. Further mammalian specimens (including those of a eutherian mam­ mal) were found in Toogreeg by Dr. Barsbold and his co-workers in 1976, 1* 116 ZOFIA KIELAN-JAWOROWSKA & DEMBERLYIN DASHZEVEG during the field work of the Soviet-Mongolian Palaeontological Expedi­ tion (personal information from Dr. R. Barsbold). These now are housed in the Palaeontological Institute of the USSR Academy of Sciences in Moscow. It has been claimed by various authors (see Maryanska and Osm6lska 1975, and Gradziilski et al. 1977, for reviews) that the Toogreeg beds (informally called by Maryanska and Osm6lska 1975, the Toogreeg for­ mation) are stratigraphic equivalents of the Djadokhta Formation. The age of the latter has been tentatively determined by Gradzinski et al., (1977) as ?late Santonian and/or ?early Campanian. It is possible that the occurrence in Toogreeg beds of a multituberculate, unknown in the Djadokhta Formation, is the result of different ecological conditions pre­ vailing during deposition of the two formations. However, the possibility that the rocks of the Toogreeg beds are somewhat younger or older than those of the Djadokhta Formation cannot be excluded. Because of the lack of more detailed data, and because the age of the Djadokhta Formation has been determined within wide time limits, we tentatively accept the interpretation that the Toogreeg beds are a stratigraphic equivalent of the Djadokhta Formation. We express our gratitude to Prof. W. A. Clemens (University of California, Berkeley) and Dr. D. J. Archibald (Yale University, New Haven) for reading the manuscript and comments. The following persons from the technical staff of the Institute of Paleobiology (Zaklad Paleobio­ logii) of the Polish Academy of Sciences in Warsaw helped us in prepara­ tion of this paper: Mrs Joanna Skarzynska preparing the specimen and Mrs. K. Budzynska making the drawings after our pencil sketches. Abbreviations used for Institutions: ZPAL Institute of Paleobiology (Zaklad Paleobiologii) of the Polish Academy of Sciences, Warsaw. GISPS Geological Institute, Section of Palaeontology and Stratigraphy the Academy of Sciences of the Mongolian People's Republic, Ulan Bator. SYSTEMATICS AND ANATOMY Family Eucosmodontidae (Jepsen, 1940) Discussion. - Kielan-Jaworowska (1974: 30) stated that there is: "One pair of palatal vacuities" in eucosmodontids. She also mentioned (Kielan­ 4 -Jaworowska 1970: 45): "... palatal vacuity slender, situated opposite p ", in the diagnosis of Kryptobaatar dashzevegi, assigned to the Eucosmo­ dontidae. When the paper by Kielan-Jaworowska (1970) was submitted for publication, the collection of K. dashzevegi from Bayn Dzak included NEW CRETACEOUS MAMMAL LOCALITY 117 several specimens, all lacking braincases. The palate is cracked in the best preserved specimen, chosen as the holotype of K. dashzevegi (ZPAL MgM-I/21), suggesting the presence of palatal vacuities (see Kielan-Ja­ worowska 1970, pI. 14:1b). New better preserved material of this species, collected by members of subsequent Polish-Mongolian Expeditions, shows that the palatal vacuities are lacking in Kryptobaatar. They are also lacking in Tugrigbaatar gen. n., assigned to the Eucosmodontidae. It follows that the diagnosis of the Eucosmodontidae should be emended: palatal vacuities are either present or absent in members of this family. If the skull structure of eucosmodontid genera was better known (see list in Kielan-Jaworowska 1970: 30, and in addition Buginbaatar Kielan-Ja­ worowska and Sochava, and Tugrigbaatar gen. n.) it might prove that this family is not a natural unit. Some genera, now assigned to the Eucosmodontidae might in future be separated to constitute a new family. Genus Tugrigbaatar nov. Type species: Tugrigbaatar saichanensis sp. n. - the only species known. Tugrigbaatar saichanensis sp. n. (pIs 1-4; figs 1-5) Derivation of the name: generic - from the locality of Toogreeg in the Gobi Desert and from Ulan Bator (Ulan Baatar); specific - from Gurvan Saykhan mountain range. Holotype (the only known specimen): GISPS 8-2 PST, almost complete, damaged skull, associated with mandibles and fragments of the postcranial skeleton. ' Type horizon and locality: Toogreeg beds, ?late Santonian and/or ?early Campanian; locality of Toogreeg, Gobi Desert, Mongolia. 2042 Generic and specific diagnosis. - Dental formula 1622 Relatively small eucosmodontid, length of the skull about 30 mm. Snout roughly rectangular in front of zygomatic arches, which are confluent with lateral margins of the snout. Frontals taper anteriorly toward a common point. Lacrimal, as seen in dorsal view, probably roughly rectangular. Premaxilla short, relatively shorter than in Kryptobaatar. Small round foramen of unknown function (?incisive foramen) in the palatal part of premaxilla. Palatal vacuities lacking. Glenoid fossa probably small, situated far laterally on the stout root of the zygomatic arch. .Intersection 118 ZOFIA KIELAN-JAWOROWSKA & DEMBERLYIN DASHZEVEG of occipital plane and occlusal plane of the teeth at approximately a right angle. Basicranial region poorly known. Lower jaw massive, posterior part strongly bent laterally. Condyle small. Upper tooth row straight in horizontal and vertical planes, with p. protruding ventrally. pi and p 2 TUGRIGBAATAR KRYPTOBAATAR 5mm Fig. 1. Diagrammatic drawing of the skulls of Tugrigbaatar saichanensis sp. n.. (left) and Kryptobaatar dashzevegi Kielan-Jaworowska (right), in palatal view, showing the differences between the two genera. have 3 cusps; p a - number of cusps unknown; p4 with ?4 cusps in the middle row, number of other cusps unknown; cusps ?4:4:ridge on Ml; 2 1 I 1:2:3 on M • Inner ridge on M probably denticulated. P4/M length ratio 0.76. P3 small, peg-like; P 4 arcuate with unidentified number of serrations possibly ?7 or 8 provided with ridges. Cusps 4:3 on M I and 4:2 on M2 • F 4/M1 length ratio about 1.3. NEW CRETACEOUS MAMMAL LOCALITY 119 Comparisons of the measurements of the dentition of T. saichanensis and K. dashzevegi ----- Tugrigbaatar I Species Kryptobaatar dashzevegi saichanensis ZPAL MgM-I/21 Mus. cat. no. GISPS 8-2PST ZPAL MgM-I/6 IGISPS 8· holotype I -3PST p 4 1ength 2.3 2.1 2.2 2.2 M 1 1ength 3.0 2.5 2.6 2.6 width 1.l> 1.5 1.5 1.6 M1length 2.6 2.1 1.9 2.0 width 1.9 1.7 1.7 P4 1ength 3.0 2.7 2.6 -- M 1 1ength 2.3 2.1 2.3 width 1.2 1.2 M 2 1ength 1.8 1.6 1.6 width 1.5 1.4 1.5 ~~ DESCRIPTION SKULL Snout and zygoma. - The nasals are extensive and strongly expanded posteriorly. The median processes of the frontals are deeply inserted between the nasals, probably forming a pointed end. The posterior pair of deep "vascular" foramina is preserved on the nasals, the anterior ones are not preserved. The premaxilla is short, directed vertically, except for the most dorsal segment. The premaxilla-maxillary suture extends almost vertically along the lateral wall of the snout. The infraorbital foramina, parts of lateral walls of the maxillae, and the anterior parts of zygomatic arches are not preserved. Only the posterior part of zygo­ matic arch is preserved on the right side of the skull. The glenoid fossa is incompletely preserved. Judging from the preserved fragment it was comparatively small, roughly -oval and almost flat. It is situated far la­ terally, separated from the basicranial region by a stout root of the posterior part of the zygomatic arch, which is directed more transversely than longitudinally. Palate. - The palatal processes of the premaxillae form concave sur­ faces, anteroposteriorly shorter than in other eucosmodontids, occupying about one third of the palatal length; A small round foramen of unknown function is present on the premaxilla at mid-length between P and 12. 120 ZOFIA KIELAN-JAWOROWSKA & DEMBERLYIN DASHZEVEG Smm Fig. 2. Tugrigbaatar saichanensis sp. n.: reconstruction of the skull and lower jaw in lateral view. It might be an incisive foramen. It is too small to be interpreted as an alveolus of an additional incisor. Also, as demonstrated by Hahn (1971), of the three pairs of the upper incisors present in the Jurassic Paul­ choffatidae, the first was lost, and the two pairs occuring in the late Cretaceous multituberculates are II and P.
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