Morphological diversity of saber-tooth upper canines and its functional implications

Elongated upper canine teeth, commonly known as saber-teeth, have evolved three times within the sub-order Feliformia. The species that wielded them flourished throughout the Cenozoic and have historically been separated into two morphological groups: the dirk-tooths with longer, flatter canines, and the scimitar-tooths with shorter, serrated teeth. However, quantitative morphological analysis has not been conducted on these teeth to determine the true amount of diversity within the group, and how the upper canine morphology of extant feliforms compared to their extinct relatives has also not been explored. Using Geometric Morphometric analysis, it is shown that saber-tooth upper canine morphology is exceptionally diverse, with no extant clade having all its members occupy the same morphospace based on tooth length and curvature. Instead, a neutral basal morphospace is observed for all groups and diversification from this basal position is seen as species become more derived. A distinct and consistent scimitar tooth morphology is also not observed within the morphospace. When compared with extant taxa, several saber-tooth species are seen to be morphologically similar to extant feliforms, several of which exhibit novel dietary strategies in comparison to the obligate carnivore felids. Biomechanical analyses of different actual and theoretical tooth shapes demonstrate that saber-teeth upper canines further represent a functional compromise between sharpness, curvature, and length on the one hand, and robustness and material investment on the other.