Kielantherium, a basal tribosphenic mammal from the Early Cretaceous of Mongolia, with new data on the aegialodontian dentition

Two additional specimens of the basal tribosphenid mammal Kielantherium gobiense, the first known aegialodont upper molar (possibly M2) and a dentary fragment with m1, are described from the Early Cretaceous Höövör locality in Mongolia. The upper molar shows an initial stage of the protocone development. Kielantherium gobiense has been known from two specimens only, and thus the new material doubles the hypodigm of this species. Kielantherium is clearly not a junior synonym of Aegialodon, as it differs from the latter in having a cusp−like mesiolabial cingulid cuspule f rather than prominent ridge−like precingulid. Kielantherium's lower postcanine dental formula (with four or more premolars and four molars) is distinctive and more primitive than in Peramus and Eutheria which have five premolars and three molars, and Metatheria which have three premolars and four molars.