A sabre-tooth predator from the Neotropics: Cranial morphology of Anachlysictis gracilis Goin, 1997 (Metatheria, Thylacosmilidae), based on new specimens from La Venta (Middle Miocene, Colombia)

Abstract

The fossil metatherian assemblage from La Venta (Middle Miocene, Colombia) is one of the most diverse in South America, and it is critical to understand the Neogene radiation of this group in this continent. La Venta contains the northernmost record of Thylacosmilidae Riggs, 1933 (Metatheria, Sparassodonta): Anachlysictis gracilis Goin, 1997, the first thylacosmilid species named for the Neotropics. This taxon was described mostly based on mandibular remains. Recent fieldwork and work in collections led to the discovery of new materials for this species, including the most complete skeleton ever found for this Sparassodonta Ameghino, 1894. Here, we present a detailed description of the cranial osteology and dentition of A. gracilis, which elucidates anatomical aspects previously inferred but hitherto unconfirmed. We investigate the phylogeny, and ecomorphological parameters of this taxon (diet and body mass) to set the evolutionary context of the species, understand its paleobiology, and evaluate palaeoecological implications. Additionally, we revise the phylogeny of the thylacosmilids, recovering the traditional classification of the group, differentiated from the proborhyaenids and borhyaenids. This work also proposes a new reconstruction of the external morphology of the head of A. gracilis based on 3D scans of the new referred materials.