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.

Off the script and crypt: the systematic affinities and evolutionary significance of an unexpected Sparassodonta (Mammalia, Metatheria) from Itaborai Basin (early Eocene)

“…The maxillae assigned to Xenocynus gen. nov. display deep pits between the upper molars, specially between M3-4, which is a compatible morphology to the presence of large protoconids in lower molars (see Suarez et al 2023). Based on the relative size of these maxillary pits (see Fig.…”

“…2a), it is deductible that the protoconid of m4 e clearly more developed than the one of m3, and this one from the one of m2. This pattern is observable in most sparassodonts due to the increase in the size of the lower molars from m1 to m4 (see e.g., Rangel et al 2019Rangel et al , 2023aRangel et al , 2023bSuarez et al 2023). This morphology and the presence of short (= mesio-distally compressed) lingual alveolus of upper molars support the identi cation of these maxillae to a Sparassodonta.…”

“…There are deep pits (sensuSuarez et al 2023) between the upper molars in MCT.M.2382 (holotype), MCT.M.4590 and MCT.M.4606, in which the one between M3-4 as the deepest pit. Dental measurements (in mm) of Xenocynus paradoxus gen. et sp.…”