Data S12. 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、多元素颌骨到多元素耳、单元素颌骨的演化转变，是脊椎动物最引人注目的结构转型之一。针对该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，同样是此次演化辐射（evolutionary radiation）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，但其颌骨刚度却呈现出出人意料的刻板模式。这种基于强度的形态功能体制（morphofunctional regime）具有遗传基础，使得哺乳动物颌骨能够有效抵御形变——即便它们在演化辐射中演化出了形态差异极大、食性截然不同的类群。将听觉与咀嚼（mastication）功能解耦，对下颌骨带来的主要功能影响，是相较于非哺乳动物，颌骨刚度提升与机械效率、运动速度下降之间的权衡取舍（trade-off）。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学多样化奠定了基础。本文隶属于主题专栏"The mammalian skull: development, structure, and function"（哺乳动物头骨：发育、结构与功能）。