Jaw function in Smilodon fatalis: a reevaluation of the canine shear-bite and a proposal for a new forelimb-powered Class 1 Lever Model

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.

Comparing cranial biomechanics between Barbourofelis fricki and Smilodon fatalis: Is there a universal killing-bite among saber-toothed predators?

Saber-tooths, extinct apex predators with long and blade-like upper canines, have appeared iteratively at least five times in the evolutionary history of vertebrates. Although saber-tooths exhibit a relatively diverse range of morphologies, it is widely accepted that all killed their prey using the same predatory behavior. In this study, we CT-scanned the skull of Barbourofelis fricki and compared its cranial mechanics using finite element analysis (FEA) with that of Smilodon fatalis. Our aim was to investigate potential variations in killing behavior between two dirk-toothed sabretooths from the Miocene and Pleistocene of North America. The study revealed that B. fricki had a stoutly-built skull capable of withstanding stress in various prey-killing scenarios, while the skull of S. fatalis appeared less optimized for supporting stress, which highlights the highly derived saber-tooth morphology of the former. The results may indicate that B. fricki was more of a generalist in prey-killing compared to S. fatalis, which experiences lower stresses under stabbing loads. We hypothesize that morphological specialization in saber-tooths does not necessarily indicate ecological specialization. Our results support the notion that morphological convergence among saber-toothed cats may obscure differences in hunting strategies employed to dispatch their prey. Our findings challenge the assumption of the universally assumed canine-shear biting as the prey-killing behavior of all saber-toothed cats. However, further research involving a wider range of dirk and scimitar-toothed forms could provide additional insights into the diversity of cranial biomechanics within this fascinating group of extinct mammalian predators.

Impact of transition to a subterranean lifestyle on morphological disparity and integration in talpid moles (Mammalia, Talpidae)

BACKGROUND

Understanding the mechanisms promoting or constraining morphological diversification within clades is a central topic in evolutionary biology. Ecological transitions are of particular interest because of their influence upon the selective forces and factors involved in phenotypic evolution. Here we focused on the humerus and mandibles of talpid moles to test whether the transition to the subterranean lifestyle impacted morphological disparity and phenotypic traits covariation between these two structures.

RESULTS

Our results indicate non-subterranean species occupy a significantly larger portion of the talpid moles morphospace. However, there is no difference between subterranean and non-subterranean moles in terms of the strength and direction of phenotypic integration.

CONCLUSIONS

Our study shows that the transition to a subterranean lifestyle significantly reduced morphological variability in talpid moles. However, this reduced disparity was not accompanied by changes in the pattern of traits covariation between the humerus and the mandible, suggesting the presence of strong phylogenetic conservatism within this pattern.