Reappraisal of a multituberculate mammal Buginbaatar transaltaiensis from the Upper Cretaceous of Mongolia

A multituberculate mammal Buginbaatar transaltaiensis from the Upper Cretaceous (Maastrichtian) Nemegt Formation at the Khaychin Ula I locality in the Gobi Desert, Mongolia, is herein redescribed based on high-resolution computed tomography (CT) scans. It is more derived than multituberculates from the Campanian Djadokhta and Barungoyot formations of the Gobi Desert in having a P4 that is less than half the labiolingual width than the M1, a greater number of cusps on M1 and m1, and in the labial row of P4, a longer lingual cusp row on M1, subcrescent molar cusps, p3 absent, and p4 with a reduced cusp number and labial and lingual ridges. Our phylogenetic analysis does not support the recognition of a monophyletic Djadochtatherioidea. Contrary to the prevailing view, the Late Cretaceous Mongolian multituberculates constitute a paraphyletic array of taxa that underwent a gradual acquisition of derived traits, ultimately resulting in the emergence of the Taeniolabidoidea. Taeniolabidoidea have an Asiatic origin with Buginbaatar placed as outgroup according to the employed phylogenetic definition. The Late Cretaceous (Maastrichtian) East Asian multituberculate taxa Yubaatar and Erythrobaatar are basally divergent taeniolabidoids.