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，从单骨中耳、多骨颌向多骨中耳、单骨颌的演化转变，堪称脊椎动物中最引人注目的结构革新之一。针对这一演化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，冠群哺乳动物极为多样的颌骨形态，竟与高度模式化的颌骨刚度紧密耦合。这种基于强度的形态功能范式具有遗传基础，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，仍能有效抵御变形。相较于非哺乳动物，将听觉与咀嚼功能解耦后，下颌的主要功能权衡表现为：颌骨刚度得以提升，但机械效率与运动速度随之下降。这种在颌骨形态与功能上的根本性、具有深远影响的转变，为冠群哺乳动物的生态与分类学多样化奠定了核心基础。本文属于专题特刊《哺乳动物颅骨：发育、结构与功能》的组成部分。