Catopsbaatar
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 Period, 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 latter is the genus' most complete specimen. "Catopsbaatar" was a member of the family Djadochtatheriidae.
Catopsbaatar
The only "Catopsbaatar" specimen which preserves the postcranial skeleton is PM120/107, which is fragmentary. It includes elements which are unknown, or incompletely preserved, in other multituberculates. One lumbar vertebra (the fifth or sixth, from between the rib cage and the pelvis) had a spinous process which was stout in side view and long when seen from above. The clavicle was slightly less curved than that of "Kryptobaatar" (resembling a bent rod which widened at each end), and measured about . The upper part of the scapulocoracoid was relatively wide in side view, and the lower part was very narrow. It was probably about long when complete. The preserved part of the humerus (upper arm bone) was about long. Its shaft was triangular in cross-section, relatively narrow when seen from above, and most of its width was occupied by the intertubercular groove. This groove was delimited on the side by the crest of the greater tubercle, whose middle part formed the deltopectoral crest. The ulnar condyle, where the ulna of the lower arm articulated with the humerus, was more prominent than the radial condyle (where the radius articulated), oval, and delimited from the radial condyle by a groove. The radius was about long, with a prominent head. Its shaft was smooth, compressed from top to bottom, and oval in cross-section. The ulna was compressed sideways, flatter than the radius, and about long as preserved.
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.