Data S8. 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）演化的过渡阶段，从单元素耳、多元素颌到多元素耳、单元素颌的演化转变，堪称脊椎动物最为显著的结构转型之一。针对这一转变的研究多聚焦于哺乳动物中耳的演化，但仅由齿骨（dentary）构成的下颌骨，同样是该演化辐射的标志性特征。本研究证实，冠群哺乳动物的颌骨形态虽极具多样性，但其颌骨刚度却惊人地趋于一致。这种基于强度的形态功能模式具有遗传基础，使得哺乳动物颌骨在演化辐射为食性差异显著的各类迥异形态时，仍能有效抵御形变。听觉与咀嚼功能解耦后，下颌骨的主要功能权衡表现为：相较于非哺乳动物，颌骨刚度更高，但机械效率与运动速度却有所下降。颌骨形态与功能的这一根本性且意义深远的转变，支撑了冠群哺乳动物的生态与类群多样性。本文隶属于专题刊《哺乳动物颅骨：发育、结构与功能》（The mammalian skull: development, structure, and function）。