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
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.