A deltatheroidan mammal from the Upper Cretaceous Baynshiree Formation, eastern Mongolia

Deltatheroidans are a specialized group of basal metatherians with a long fossil history and a broad geographic distribution across Asia and North America. The group was among the first Mesozoic mammals known by relatively complete cranial material, recovered from the Gobi Desert by the American Museum expeditions in the 1920s. Deltatheroidans exhibit trends in their dentition towards apparent specializations for carnivory, including strongly developed postmetacrista, pronounced postvallum-prevallid shear, and a reduction of the ultimate molar. While the oldest undisputed deltatheroidans hail from the Early Cretaceous of North America, Upper Cretaceous rocks in central Asia have yielded the best preserved specimens and the bulk of the diversity. Here we describe a new deltatheroidan, Tsagandelta dashzevegi, gen. et sp. nov., from the Upper Cretaceous Baynshiree Formation of eastern Mongolia. This taxon adds to the diversity of the group in central Asia and provides further evidence of uniformity among the Late Cretaceous vertebrate faunas across the Gobi Desert.