First Multituberculate Mammal From the Upper Cretaceous Nemegt Formation at Gurilin Tsav Locality in Mongolia

The multituberculates were dominant mammals in the Campanian ecosystems of Djadokhta and Barungoyot formations of Mongolia, where they were represented by an endemic Asiatic clade Djadochtatherioidea. In contrast, only one multituberculate species, Buginbaatar transaltaiensis Kielan-Jaworowska et Sochava, 1969, is present in the Maastrichtian Nemegt Formation of Mongolia, provisionally attributed to the North American clade Cimolomyidae. It is known by cranial remains from the Khaychin Ula locality. Here we report on a multituberculate distal humerus fragment from the Gurilin Tsav locality, the second occurrence of multituberculates from the Nemegt Formation. This humerus is most similar with the humerus from the Maastrichtian Hell Creek Formation of Montana, USA, tentatively attributed to a cimolomyid Menisceessus robustus (Marsh, 1889). If the Gurilin Tsav humerus belongs to Buginbaatar, this may support attribution of this taxon to Cimolomyidae.