Morphological evidence supports Dryolestoid affinities for the living Australian marsupial mole Notoryctes

Recent discoveries demonstrated that the southern continents were a cradle for the evolutionary radiation of dryolestoid mammals at the end of the Cretaceous. Moreover, it becomes evident that some of these early mammals surpassed the K/T boundary in South America, at least. Notoryctes is a poorly known living mammal, currently distributed in the deserts of central Australia. Due to its extreme modifications to fossoriality and peculiar anatomy, the phylogenetic relationships of this genus were debated in the past, but most recent authors agree in its marsupial affinities. A comparative survey of the anatomy of Notoryctes reveals the poorly sustained marsupial affinities for the genus and striking plesiomorphies for a living mammal. Surprisingly, Notoryctes exhibits similarities with dryolestoids. Dryolestoids were a diverse and mainly mesozoic mammalian group phylogenetically nested between the egg-lying monotremes and derived therians. In particular, Notoryctes share a number of shared features with the extinct dryolestoid Necrolestes, from the Miocene of Patagonia. Both taxa conform a clade of burrowing and animalivorous dryolestoids that survived other members of their lineage probably due to their peculiar habits. Accordingly, Notoryctes constitutes a “living-fossil” from the supposedly extinct dryolestoid radiation, extending the biochron of the group more than 20 million years to the present day. The intermediate phylogenetic position of Notoryctes has the pivotal potential to shed light on crucial anatomical, physiological, ecological, and evolutionary topics in the deep transformation from egg-lying to placental mammals. This finding, together with the Australian monotremes, constitutes the second example of early mammals that survived in Gondwana well after the KT boundary.