Abstract

A new sparassodont metatherian, Dimartinia pristina gen. et sp. nov., is described based on a specimen from the Late Miocene (Chasicoan Stage/Age) of the Argentine Pampas. The new taxon shows several characters that resemble a more generalized condition of the thylacosmilid morphology (e.g., reduced incisor formula –with no more than two incisors, laterally compressed lower canine, p1–2 homodont and smaller than p3, non-fusiform anterior portion of the horizontal ramus). For each of them, D. pristina has a generalized condition (less developed) compared to members of the family Thylacosmilidae. However, the phylogenetic analysis does not recover this new species within this family but in a more basal position, closely related to it. Our paleobiological analyses reveal that D. pristina was a small hypercarnivore with a body mass of around 3 kg. Most of its derived features, similar to those of thylacosmilids, occur at the anterior-most part of the rostrum (in the lower jaw, at the symphyseal region), suggesting that the evolution of this area involved modular developmental processes. Additionally, several pathological marks on the lateral surface of the horizontal ramus indicate that the individual suffered a traumatic bone lesion with linear lysis processes and peripheral periosteal reaction that was not remodelled. The degree of periosteal reaction allows us to estimate that the individual survived at least 15 days after the occurrence of the injury.