Craniodental anatomy of a new late cretaceous multituberculate mammal from Udan Sayr, Mongolia

The multituberculate Mangasbaatar udanii gen. et sp. n., represented by two specimens from Udan Sayr locality in the Gobi desert (Mongolia), is a derived member of a speciose group of Late Cretaceous Mongolian multituberculates (LCMM), clustering together with large-size forms such as Catopsbaatar, Tombaatar, and Djadochtatherium, forming a monophyletic group. Tombaatar sabuli is the sister taxon and shares with the new form the dental formula, overall dental morphology, and approximate size. The new multituberculate has a very large middle ear cavity, housing a petrosal and promontorium that are deeply sunk into the braincase. The expansion of the middle ear cavity seems to be absent among basal LCMM, only developing among members of Djadochtatherioidea, and to an extreme degree in the Udan Sayr multituberculate and Tombaatar. Among living mammals, enlarged middle ear cavities confer enhanced low frequency audition and are often found in fossorial species, such as golden moles, and several groups of rodents adapted to open, arid environments. Burrowing is a possible behavior for the new mammal and its closest relatives with similarly expanded middle ear regions and an arid environment has been proposed for the sediments where most LCMM are found. The new taxon further demonstrates the morphological, and possibly ecological, diversity among multituberculates.