Udanoceratops

Udanoceratops (meaning "Udan-Sayr horned face") is a genus of large leptoceratopsid dinosaur that lived during the Late Cretaceous period of Mongolia. The holotype specimen, the partial skeleton of an adult with its bones encapsulated in calcium carbonate, was discovered in the 1980s as part of the Joint Soviet-Mongolian Paleontological Expedition, and was subsequently transported to the Paleontological Institute of the Russian Academy of Sciences. In 1992, it was described by palaeontologist Sergei Kurzanov. The sole species of Udanoceratops, also the type species, is Udanoceratops tschizhovi, named after a colleague of Kurzanov, D. O. Tschizhov. Additional remains have been assigned to Udanoceratops, though these may be misattributions.

Udanoceratops is the largest known leptoceratopsid, with some estimates placing it at about 4 m (13 ft) in length and 700 kg (1,500 lb) in weight. Its skull, though incomplete, probably was between 60–70 cm (24–28 in) in length, half as long again as that of the second-largest leptoceratopsid, Montanoceratops from North America. Udanoceratops' skull was far deeper and more robust than that of other leptoceratopsids, with larger nasal cavities and presumably a heavier beak. The projections on Udanoceratops' cheek bones would have supported a large patch of keratin. The bone of its snout above the beak was completely smooth, bearing neither the horns nor the slight tubercles of related taxa. Udanoceratops had a very deep and robust lower jaw (mandible), capable of exerting a powerful bite, possibly strong enough to cleave through bone; indeed, the holotype bears damage to its mandible which may have been caused by such a bite. The lower teeth bore shelves into which the upper set would have slotted when the jaw was closed. This would have resulted in a slicing action, similar to the system present in Archaeoceratops and Leptoceratops.

The postcranial skeleton of Udanoceratops is fragmentary, consisting primarily of a partial vertebral column and a few appendicular bones. Its tail was very tall and was somewhat compressed from side-to-side, as in many other leptoceratopsids and protoceratopsids. This and the shape of its unguals (the bones which would have supported its claws) has led to suggestions that Udanoceratops was semi-aquatic, but it is more likely that the shape of its unguals was an adaptation to supporting its weight on soft substrate such as sand dunes. Similarly, while it has been suggested that Udanoceratops could have run bipedally, this appears to be unlikely. If it did run, it likely would have done so on all fours, and would have been significantly slower than its smaller relatives. Udanoceratops is known from the Djadochta Formation of Mongolia, which is well known for the fossils of Protoceratops and Velociraptor which have been recovered there. Specifically, the Udan-Bayr locality, from which the holotype of Udanoceratops was recovered, preserves fossils of Protoceratops and the oviraptorosaur Avimimus.