Data S15. from A switch in jaw form–function coupling during the evolution of mammals

The evolutionary shift from a single-element ear, multi-element jaw to a multi-element ear, single-element jaw during the transition to crown mammals marks one of the most dramatic structural transformations in vertebrates. Research on this transformation has focused on mammalian middle-ear evolution, but a mandible comprised only the dentary is equally emblematic of this evolutionary radiation. Here, we show that the remarkably diverse jaw shapes of crown mammals are coupled with surprisingly stereotyped jaw stiffness. This strength-based morphofunctional regime has a genetic basis and allowed mammalian jaws to effectively resist deformation as they radiated into highly disparate forms with markedly distinct diets. The main functional consequences for the mandible of decoupling hearing and mastication were a trade-off between higher jaw stiffness versus decreased mechanical efficiency and speed compared to non-mammals. This fundamental and consequential shift in jaw form–function underpins the ecological and taxonomic diversification of crown mammals.This article is part of the theme issue ‘The mammalian skull: development, structure, and function’.

在向冠群哺乳动物（crown mammals）过渡的过程中，从单元素耳、多元素颌骨向多元素耳、单元素颌骨的演化转变，堪称脊椎动物界最引人注目的结构转型之一。此前针对这一演化转型的研究多聚焦于哺乳动物中耳演化，但仅由齿骨（dentary）构成的下颌骨，同样是这一演化辐射的标志性特征。本研究表明，冠群哺乳动物形态极为多样的下颌骨，却对应着惊人统一的下颌刚度。这种基于强度的形态功能模式具有遗传基础，使得哺乳动物下颌在辐射演化出形态迥异、食性截然不同的类群时，仍能有效抵抗变形。听觉与咀嚼功能解耦后，下颌产生的主要功能权衡为：相较于非哺乳动物，具备更高的下颌刚度，却伴随着机械效率与运动速度的下降。这一颌骨形态-功能层面的根本性且意义深远的转变，为冠群哺乳动物的生态与分类学多样性奠定了核心基础。本文隶属于专题刊‘哺乳动物颅骨：发育、结构与功能’。