Cranial morphology of the Miocene thylacinid Mutpuracinus archibaldi (Thylacinidae, Marsupialia) and relationships within the Dasyuromorphia

Abstract

A plesiomorphic middle Miocene thylacinid, Mutpuracinus archibaldi, closely resembles the early to middle Miocene dasyurid, Barinya wangala, in its possession of purportedly exclusive dasyurid characters: a closed alisphenoid tympanic bulla that contacted a periotic tympanic sinus; a deeply invasive internal jugular canal with a distinct posteroventral lip of the petrosal; and a rudimentary tubal foramen. These shared character states and many other structural similarities in the cranial base between Mutpuracinus and Barinya indicate shared ancestry, with the dentally more conservative Dasyuridae representing the plesiomorphic sister group to the Thylacinidae. Other Oligocene-Miocene thylacinid species in which the bony ear region is preserved (Badjcinus turnbulli, Nimbacinus dicksoni) show intermediate states between Mutpuracinus archibaldi and Thylacinus cynocephalus. These indicate that the states of the ear region of Thylacinus cynocephalus (small, posteriorly open alisphenoid tympanic wing, absence of petrosal tympanic process, alisphenoid surrounding primary foramen ovale), which resemble some South American didelphoid marsupials, are not primitive. They are secondarily derived states in which the alisphenoid tympanic wing and contacting processes are reduced.