Data S4. 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）的演化过渡阶段中，从单骨耳、多骨颌向多骨耳、单骨颌的演化转变，堪称脊椎动物领域最具代表性的结构转型事件之一。此前针对该转型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，同样是此次演化辐射的标志性特征。本研究表明，冠群哺乳动物的颌骨形态虽呈现出显著多样性，但其颌骨刚度却表现出出人意料的定型化特征。这种以强度为核心的形态功能模式具有遗传基础，使得哺乳动物的颌骨在辐射演化出形态迥异、食性截然不同的类群时，仍能有效抵御变形。听觉与咀嚼功能分离后，下颌骨所面临的主要功能权衡为：相较于非哺乳动物，其颌骨刚度更高，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影响深远的转变，为冠群哺乳动物的生态与分类多样性奠定了核心支撑。本文隶属于专题刊"哺乳动物颅骨：发育、结构与功能"。