FEA models from "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.

修长的上犬齿，俗称剑齿（saber-teeth），在猫型亚目（Feliformia）中独立演化了三次。拥有该类齿型的物种在新生代（Cenozoic）时期广泛繁盛，历史上被划分为两类形态学类群：犬齿更长更扁平的短剑齿类（dirk-tooths），以及犬齿更短且带锯齿的弯刀齿类（scimitar-tooths）。然而，此前尚未针对这类牙齿开展定量形态学分析，以明确该类群的真实多样性水平，也未有研究探讨现存猫型亚目物种的上犬齿形态与其已灭绝近亲之间的差异。本研究通过几何形态测量学分析（Geometric Morphometric analysis）发现，剑齿类的上犬齿形态具有极高的多样性：基于齿长与齿弯曲度，没有任何一个现存演化支（extant clade）的所有成员均处于同一形态空间（morphospace）内。相反，所有类群均存在一个中性的基础形态空间，随着物种演化程度升高，类群会从该基础位置发生形态分化。此外，在形态空间中并未观测到特征明确且高度一致的弯刀齿类形态。将剑齿类物种与现存类群对比后发现，多种剑齿类的形态与现存猫型亚目物种高度相似，其中部分物种展现出区别于专性食肉猫科动物的新型食性策略。针对多种实际及理论齿形开展的生物力学分析（biomechanical analyses）表明，剑齿类上犬齿的形态本质上是在锋利度、弯曲度与齿长，以及齿坚固性和材料投入之间形成的功能性折中方案。