Analysis of functional morphology in carnassial dentitions (Carnivora, Dasyuromorphia, Hyaenodonta)

Abstract

Functional and structural changes in the evolution of carnassial teeth in the Carnivora, Dasyuromorphia and Hyaenodonta are analyzed by a combination of Occlusal Fingerprint Analysis, Dental Topographic Analysis (quantification of crown curvature by Dirichlet Normal Energy) and 3D geometric morphometrics. Carnassialization can be described as an increasing simplification of tooth structure and function. The documented tooth wear and virtual simulation of the power stroke indicate a functional shift from weakly to higher carnassialized teeth, where the cutting function is emphasized and the crushing function is reduced. In some taxa, a trenchant talonid with a hypoflexid groove evolves, performing a similar shearing and guiding function as the hypoflexid in pretribosphenic teeth, such as in dryolestids. This observation is consistent with the hypothesis that carnassialization is a simplification and structural reverse of the tooth crown to an ancestral pretribosphenic condition. The Dental Topographic Analysis of lower carnassials shows low crown curvature values in higher carnassialized teeth. The decrease of crown curvature with increasing carnassialization can be explained with the reduction of cusps and crests, which results in a simplified crown relief. The geometric morphometric analysis of lower carnassials indicates a convergent simplification of the crown relief connected to carnassial blade enlargement and talonid reduction. Along the lower tooth row of dasyuromorphs (m2 - m4) and hyaenodonts (m1 - m3) the most distal carnassial is the most carnassialized (principal carnassial), and in most taxa with overall higher carnassialized teeth, carnassialization successively increases from the mesial to the distal tooth position. Additionally, a shape difference connected to the phylogeny, showing a mesio-distal elongation of the carnassial unique to carnivorans with weakly carnassialized teeth, is indicated. The mesio-distal tooth elongation, present only in caniforms and unspecialized feliforms (viverrids and herpestids), enables the presence of a functional crushing talonid basin and a longitudinally oriented carnassial blade, performing an efficient carnassial cutting. As indicated by an ancestral state reconstruction, this condition may be plesiomorphic for the Carnivora and may have provided them with an advantage in terms adaptive versatility, as it did not evolve in dasyuromorphs or hyaenodonts.