Saber-tooth Thylacosmilidae (Mammalia, Metatheria, Sparassodonta): a review of diversity and relationships.

FORASIEPI, A.M.

Mendoza

Congreso; X International Mammalogical Congress; 2009

IADIZA

Thylacosmilids (Mammalia, Metatheria, Sparassodonta) were one of the most bizarre native predators from the Tertiary of South America. The external appearance of the skull evidences anatomical resemblances with the saber-tooth felids (Eutheria, Felidae, Machairodontinae), mostly based on the acquisition of large hypertrophied upper canines. The family Thylacosmilidae was originally defined to include the genus Thylacosmilus, which currently comprises a unique species: T. atrox (=Achlysictis lelongi) from the late Miocene- middle Pliocene (Huayquerian, Montehermosan, and Chapadmalalan) of Argentina and possibly the late Miocene (Huayquerian) of Uruguay. A second species, Anachlysictis gracilis, from the middle Miocene (Laventan) of Colombia was later described, with more generalized morphology with regard to Thylacosmilus. In addition to these two species, there are other materials tentatively assigned to Thylacosmilidae, such as a fragmentary specimen from the middle Miocene of Colombia and a single tooth from the early Miocene (Colhuehuapian) of Patagonia. Based on the latter, the time span for the group ranges from early Miocene to middle Pliocene (Colhuehuapian to Chapdmalalan ages). A new material that corresponds to a fragmentary skull from the middle Miocene (Colloncuran) of Patagonia is currently under study, and represents a new genus and species. The features on the dentition suggest that this new Patagonian taxon was probably closer to Thylacosmilus than Anachlysictis. Thylacosmilids were classically related to proborhyaenids, but the monophyletic nature of the latter is currently under debate. Instead and based on a recent analysis, thylacosmilids may represent the sister taxon of early Miocene borhyaenids (i.e., Borhyaena and Arctodictis) and a late Oligocene proborhyaenid (i.e., Paraborhyaena). Considering the known data from the fossil record, and if this hypothesis of relationships is correct, there is a ghost linage of more than five million years for the family Thylacosmilidae.