An exceptionally well-preserved skeleton of Palaeothentes from the Early Miocene of Patagonia, Argentina: new insights into the anatomy of extinct paucituberculatan marsupials

During the Cenozoic paucituberculatans were much more diverse taxonomically and ecomorphologically than the three extant genera of shrew-like marsupials. Among paucituberculatans, palaeothentids were abundant during the Early Miocene, although most of the fossil remains consist of isolated teeth or fragmentary jaws. We describe a new and exceptional partial skeleton of Palaeothentes lemoinei (Palaeothentidae), collected from the Santa Cruz Formation (Santacrucian age, Early Miocene) in Patagonia. Whereas the skull of P. lemoinei has more plesiomorphic traits in the face, palate, and cranial vault than that of living paucituberculatans, the dental morphology is more derived. The osseous inner ear was examined using micro-CT scanning, revealing a cochlea with 1.9 turns, the presence of a "second crus commune”, an anterior semicircular canal (SC) projecting slightly dorsally from the dorsal-most point of the posterior SC, and lateral and posterior SCs projecting laterally to the same level. On the basis of postcranial anatomy, previous studies have demonstrated that P. lemoinei was an agile cursorial form, an inference supported by study of the new postcranial elements