MIOCENE SABER-TOOTH PREDATORS FROM THE NEOTROPICS: THE THYLACOSMILIDS FROM NORTHERN SOUTH AMERICA

The metatherians (marsupials and extinct relatives) span from the Lower Cretaceous to the present. The Sparassodonta (Mammalia, Metatheria) were the dominant predator mammals in South America during most of the Cenozoic, sharing the carnivorous niche with birds (phorusrhacids) and large reptiles. The South American saber-tooth predators, the Thylacosmilidae (Sparassodonta), stand among the most notable and specialized carnivore metatherians.

The fossil metatherian assemblage from La Venta (middle Miocene, Colombia) is one of the most diverse of the Neogene in South America and crucial to the knowledge of the metatherian Neogene radiations in this continent. It contains the northernmost record of thylacosmilids, the only one with more than one species. Anachlysictis gracilis, one of them, was described mostly based on mandibular remains, but the holotype preserves undescribed elements. Recent work in collections and fieldwork led to the discovery of new materials, including the most complete skeleton ever found for Anachlysictis (one of the most complete for Sparassodonta). The other species was previously referred with doubts to this family, partially described and not named. However, the present contribution not only names and describes this species but also confirms it as a basal thylacosmilid.

This research includes detailed descriptions of the two species based on the holotypes and new materials. Additionally, phylogenetic and paleobiological analyses are performed to understand their evolutionary frame and autecological role in the family. This work also discusses and refutes the classification of Eomakhaira molossus, recently described as a thylacosmilid, which lacks all the Thylacosmilidae synapomorphies. Consequently, the family would be represented by the species Thylacosmilus atrox, Patagosmilus goini, Anachlysictis gracilis, and the new species from La Venta. Additionally, a new species from Argentina is described in a work in progress, parallel to this research.

This contribution is relevant to the knowledge about Thylacosmilidae and Sparassodonta in terms of phylogeny, paleobiology, paleoecology, and paleobiogeography. It is also crucial to update the knowledge about the La Venta metatherians and their implications on the radiations of South American Cenozoic metatherians.