Catopsbaatar

-aged fossil localities of Mongolia; Catopsbaatar was collected in area A (Khermeen Tsav I, II, and Khulsan at the left) In 1970 and 1971, the Polish-Mongolian Palaeontological Expeditions collected mammalian fossils from the Barun Goyot Formation at the Red Beds of Hermiin Tsav (also spelled "Khermeen Tsav") area in Mongolia's Gobi Desert. About 100 specimens, recovered from four localities, are housed at the Polish Academy of Sciences in Warsaw. Two-thirds of the collected specimens were multituberculates: an extinct order of mammals with rodent-like dentition, named for the numerous cusps (or tubercles) on their molars. In 1974, Polish palaeontologist Zofia Kielan-Jaworowska named a new species of the Mongolian multituberculate genus Djadochtatherium as D. catopsaloides, with specimen ZPAL MgM−I/78 from the Polish collection as the holotype. The specific name refers to the animal's similarity to the North American species Catopsalis joyneri, which Kielan-Jaworowska thought was a possible descendant. The specimen, collected at the Hermiin Tsav I locality, is an almost-complete skull of a juvenile with portions of the cranium damaged. Kielan-Jaworowska also assigned other specimens to the species: a damaged skull missing lower jaws (ZPAL MgM−I/79, an adult), a skull with partial lower jaws (ZPAL MgM−I/80), and a molar with a fragment of jaw (ZPAL MgM−I/159 from Khulsan, the only specimen not from the Hermiin Tsav I and II localities). American palaeontologists Nancy B. Simmons and Miao Desui conducted a 1986 cladistic analysis which indicated that Catopsalis was a paraphyletic taxon (an unnatural grouping of species), and C. catopsaloides required its own generic name. Kielan-Jaworowska followed Simmons and Miao's suggestion, moving C. catopsaloides to its own monotypic genus in 1994, Catopsbaatar. The word catops is derived from the Greek katoptos ("visible" or "evident"); baatar is Mongolian for "hero", and the name refers to Catopsbaatar's similarity to the genus Catopsalis (as is the case for the specific name). The name Catopsalis itself consists of the Greek words for "visible" and "cutting shears" (psalis). The word baatar is used as a suffix in the names of many multituberculate genera, and alludes to the Mongolian capital Ulaanbaatar, which itself means "red hero". ==Description==

Skull are included, although these disappeared as an individual aged. The most complete adult Catopsbaatar skull (specimen PM 120/107) is long and wide, with a lower jaw. By comparison, the skull of the juvenile holotype (ZPAL MgM−I/78) is about long and wide, with a lower jaw. The largest adult skull (ZPAL MgM−I/79) is long but, since it is incomplete, its other measurements are unknown. Catopsbaatar was larger than its relatives, Kryptobaatar and Djadochtatherium. of two specimens Catopsbaatar mandible was robust and very elongated. The diastema (gap between the front and cheek teeth) was concave, and extended for 20 percent of the dentary bone (the main bone of the lower jaw). Seen from above, the diastema formed a wide shelf that sloped downwards on the inner side of the jaw. The small mental foramen was close to the upper middle margin of the diastema. The coronoid process of the mandible appears to have been relatively longer and narrower than in other djadochtatherioids. It was separated from the alveolar process (where the teeth are contained) by a wide groove. The mandibular condyle (which articulated with the skull) was slightly above the level of the molars. The front part of the masseteric crest was very prominent, forming a bulge known as a masseteric protuberance. The robustness of this crest and the presence of the protuberance varies among related genera. The masseteric fovea (pit) in front of the masseteric fossa was probably more distinct than in other djadochtatherioids. Each half of the mandibular symphysis (where the two halves of the mandible connect) was shaped like an upside-down teardrop. The pterygoid fossa on the inner side of the mandible was very large, and occupied most of the hind part of the dentary. The lower part of this fossa had a boundary, known as the pterygoideus shelf. Catopsbaatar had a single lower pair of incisors, characteristic of multituberculates, which was very strong and compressed sideways. It had a sharply limited band of enamel, and grew continually. The p3 premolar was very small, and adhered entirely to the lower diastema under the larger p4. The blade-like p4 was roughly trapezoidal in side view, and had three cusps along the horizontal upper margin and one cusp on the outer back side. The p4 did not have the ridges on the outer and inner side, as are present in other multituberculates. The m1 molar was almost symmetrical, and its cusp formula was 4:4, the size of the cusps decreasing towards the back. The m2 had a cusp formula of 2−3:2, most specimens being 2:2. The cusps on the inner side were wider than those on the outer side, the inner row of cusps was shorter than the outer one, and the hind margin of the tooth was arranged obliquely. The contact from the ischium to the ilium and pubis of the pelvis was not fused, and the front end of the ischium formed a rugose suture. The pubis was roughly triangular, with a rough suture for the ilium above and a deep groove for the ischium at the lower front. Specimen PM120/107's pelvic bones differed from those of other multituberculates in not being fused together. The presence of sutures in the pelvis of PM120/107 indicates that it was a juvenile, although the skull appears adult; the meaning of this discrepancy is unknown. The femur (thigh bone) was proportionally similar to that of Eucosmodon and Nemegtbaatar—smaller than the former, but larger than the latter. The femur was stout relative to its length, and it may have been about long. The tibia of the lower leg was about long. Seen from behind the upper side, the tibia had a deep excavation (cavity) which may be characteristic of multituberculates. Unlike most other multituberculates and other mammals, the calcaneus bone at the back of the foot had a short tuber calcanei (like some tree kangaroos), with an expanded, anvil-shaped proximal process strongly bent downwards and to the side. Catopsbaatar had an os calcaris bone on the inner side of its ankle, a feature also seen in modern male monotremes (the platypus and the echidna) and other Mesozoic mammals. The os calcaris bone was plate-like and rectangular in outline; as in monotremes, it supported the cornu calcaris in forming a spur on the outer side of the tarsus (cluster of foot bones). Unlike with other Mesozoic mammals, these two elements were not fused together in multituberculates. The cornu calcaris was triangular, with a concavity in the middle, and was long. The spur was flattened, and was thicker at its conjunction with the os calcaris (where they connected via several ridges). As the spur of PM120/107 may have been moved from its original position, it is unknown whether it faced inwards (like in the platypus). Unlike in the platypus, there was no impression of a canal for venom. The cornu calcaris of Catopsbaatar was ossified (turned into bone) and would have been covered in keratin (the horny covering seen in nails and hoofs). The cornu calcaris of the platypus consists only of keratin, and is hollow. ==Palaeobiology==

Hurum, Zhe-Xi Luo, and Kielan-Jaworowska suggested in 2006 that the spurs on the ankles of Mesozoic mammals (such as Catopsbaatar) were homologous with those of monotremes, and were a basal (or "primitive") feature lost by later therian mammals. The male platypus uses the spur to deliver venom from a gland, but it is unknown if the extinct groups were venomous as well. Mesozoic mammals were mostly small (with exceptions such as the fox-sized Repenomamus) and, although they were too small to be prey for large theropod dinosaurs, smaller theropods, large lizards, crocodiles, and birds could have fed on them. For example, mammal jaws have been found in the abdomen of a specimen of the small theropod Sinosauropteryx; the jaws belonged to Zhangheotherium, which also had spurs, and the multituberculate Sinobaatar. Since dinosaurs dominated Earth during the Mesozoic, this period has been called the "dark ages" of mammalian history. The spur, which would have been more effective if venomous, was probably used as a defensive weapon by small, early mammals. It could also have been used during intraspecific competition or predation. and pubis from the pelvis The pelvic bones of Catopsbaatar specimen PM120/107 may not have been fused because fusion occurred late in development, because it was a sexually dimorphic feature occurring only in males (unfused pelvic bones might have enabled expansion of the birth canal in females), or pelvic fusion may be a taxonomic difference between Catopsbaatar and other multituberculates. Feeding and diet Although multituberculates were thought to have been carnivores or herbivores, since American palaeontologist William A. Clemens and Kielan-Jaworowska suggested modern rat kangaroos as analogues for the group in 1979 they have been considered omnivores (feeding on both plants and animals). Posture and locomotion The limb posture of multituberculates has been debated. According to some researchers, they employed a parasagittal stance with the erect limbs under the body; others consider a sprawling stance more likely. Kielan-Jaworowska and Hurum supported the latter theory in 2006 based on the presence of hind-leg spurs, a feature they considered present only in sprawling mammals. They pointed out that all early mammals preserved in lacustrine (lake) deposits were compressed from top to bottom, suggesting a sprawling stance, whereas later mammals were preserved on their flanks. Earlier arguments for a sprawling stance include deep pelvises and features of the legs. They also suggested that the feet of multituberculates would have been plantigrade (the sole touching the ground) at rest, but digitigrade (the sole not touching the ground) when jumping and running quickly; they dismissed the idea that the forelimbs of multituberculates and other early mammals were more parasagittal than their hindlimbs. Kielan-Jaworowska and Hurum depicted Catopsbaatar with plantigrade, sprawling legs, with mobile spurs which pointed inward when preparing for attack. Although it has been suggested that multituberculates were arboreal (lived in trees), most Asian taxa were probably terrestrial; some others were fossorial, digging and living underground. ==Palaeoenvironment==

and possible interclavicle of PM120/107 All specimens of Catopsbaatar are known from the Barun Goyot Formation of the Gobi Desert, which probably dates to the late Campanian age of the Late Cretaceous epoch (about 72 million years ago). The specimens were discovered in the Red Beds of Hermiin Tsav area except for one molar from Khulsan. When Catopsbaatar was discovered, the Red Beds of Hermiin Tsav area was thought to be a distinct formation coeval (of the same geological age) with the Barun Goyot Formation, as they contain many of the same animals, but is now thought to correspond to different levels of the Barun Goyot and Nemegt formations. The rock facies of the Red Beds of Hermiin Tsav area consist of orange-coloured, thick-bedded sandstone, with a thin interbedding of light-coloured silt stones and claystones. Dinosaurs include Heyuannia, Velociraptor, Saichania, Platyceratops, Gobiceratops, and some indeterminate theropods. Reptiles include the turtle Mongolemys, the lizards Gobinatus, Tchingisaurus, Prodenteia, Gladidenagama and Phrynosomimus, and an indeterminate crocodile. The frog Gobiates and an indeterminate alexornithiform bird are also known. Ostracods include Limnocythere, Cypridea, and Eucypris. == References ==