Catopsbaatar is a genus of multituberculate, an extinct order of rodent-like mammals. It lived in what is now Mongolia during the late Campanian age of the Late Cretaceous epoch, about 72 million years ago. The first fossils were collected in the early 1970s, and the animal was named as a new species of the genus Djadochtatherium in 1974, D. catopsaloides. The specific name refers to the animal's similarity to the genus Catopsalis. The species was moved to the genus Catopsalis in 1979, and received its own genus (Catopsbaatar, Greek and Mongolian for 'visible hero') in 1994. Five skulls, one molar, and one skeleton with a skull are known; the last is the genus' most complete specimen. Catopsbaatar was a member of the family Djadochtatheriidae.
The skull of Catopsbaatar was up to long and, as in other multituberculates, proportionally large. The external appearance of these animals' heads may have been similar to those of rodents. The skull was heavy-set and wide, with the zygomatic arches strongly expanded to the sides. The eye sockets were smaller and placed further back than in its relatives, and the snout was more elongated. Catopsbaatar had semicircular ridges on the side of the skull, to which the jaw muscles were attached. The mandible was strong and very elongated. It had very robust incisors, and cheek teeth with multiple cusps (for which multituberculates are named). The pelvic bones differed from those of other multituberculates in that they were not fused to each other. Catopsbaatar had spurs on its ankles, like those of the male platypus and echidna, without evidence of a venom canal (present in the former).
The spurs of Catopsbaatar and other Mesozoic mammals may have been used for protection against theropod dinosaurs and other predators. Multituberculates are thought to have given live birth, and the fact that they had hair indicates they were homeothermic ("warmblooded"). Multituberculates would have been omnivorous; Catopsbaatar had powerful jaw muscles, and its incisors were well adapted for gnawing hard seeds, using a backwards chewing stroke. Multituberculates are thought to have had a sprawling posture, and Catopsbaatar may have been able to jump. Catopsbaatar is known from the Barun Goyot Formation, which is thought to be about 72 million years old.
Taxonomy
upright=1.5|thumb|left|alt=Preserved skeleton and diagram of bones|[[Cretaceous-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 Catopsbaatars 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).
Later in 1994, Kielan-Jaworowska and the Russian palaeontologist Petr P. Gambaryan mentioned caudal (tail) vertebrae which may have belonged to Catopsbaatar; this attribution is uncertain, since they may instead belong to the related Tombaatar (named in 1997). Catopsalis joyneri, the basis of the name C. catopsaloides, was moved to the new genus Valenopsalis in 2015.
thumb|alt=Drawings of three similar skulls; Catopsbaatar is at the bottom|Comparison of the skulls of the [[djadochtatheriids Kryptobaatar (A), Djadochtatherium (B), and Catopsbaatar (C), with muscle scars (surrounded by the zygomatic ridges) shaded]]
The following cladogram shows the placement of Catopsbaatar among other multituberculates according to Kielan-Jaworowska and Hurum, 1997:
Description
Skull
left|thumb|upright=2|alt=Three drawings of a skull|Reconstructed adult skull from above, below, and the side. Note that the upper P1 and P3 [[premolars 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.
thumb|right|upright|alt=Collection of photos of jaws with teeth|Multiple views of the [[dentaries 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.
thumb|alt=Six photos of three small pelvic bones|Stereo photos of PM120/107's [[Ischium|ischia 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
thumb|left|alt=Two diagrams of a jaw and its muscles|upright=1.3|Reconstructed jaw musculature; B1 shows superficial layers, and B2 shows second layers.
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
thumb|left|alt=See caption|Stereo photos and diagrams of PM120/107's arm bones
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. 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.