两块在博物馆中"沉睡"数十年的化石，揭开了演化史上一次关键"变形"的奥秘。《自然》近日发表 了一项关于哺乳动物演化重要进展的研究：我国科研人员首次系统提出哺乳动物颌关节演化的四阶段序 列，揭示了这一关键解剖结构变革的完整路线，为理解脊椎动物关键特征演化提供了全新视角。 （原载于《科技日报》2025-10-09 06版） 另一块是来自云南禄丰的摩根兽类化石。此项研究中，团队以这块化石为模式标本，命名了一个新 属种——禄丰曲髁兽。它的齿骨髁结构简单，由齿骨外脊末端向上弯折形成，尚未膨大为球状。这一发 现为"哺乳动物齿骨髁起源于齿骨外脊后端"的假说提供了实证，填补了演化过程中的关键形态过渡环 节。 "基于新发现，我们首次提出原始颌关节与次生关节演化的四阶段序列，清晰展现了从爬行类到哺 乳动物的颌关节转变过程。"论文通讯作者、中国科学院古脊椎动物与古人类研究所研究员毛方园说。 同时，研究还揭示出颌关节演化存在多次独立起源，以往被视为哺乳动物鉴定特征的承压性齿—鳞骨关 节，实际仅能作为哺乳型动物而非哺乳动物冠群的鉴定特征。 值得关注的是，团队还探索出多元演化驱动机制。此前流行的"体型小型化驱动假说"无法解释体型 较大的 ...

Core Insights - The article discusses a significant evolutionary transition in mammalian jaw joints, highlighting new findings that reshape the understanding of this evolutionary process [2][3]. Group 1: Research Findings - The study published in Nature reveals new evidence and hypotheses regarding the evolution of jaw joints in mammaliamorphs, based on two fossil specimens with novel secondary jaw joint morphologies [3][5]. - The first specimen, Polistodon chuannanensis, is a large herbivorous triconodont from the Middle Jurassic, exhibiting a unique dentary-squamosal secondary jaw joint, marking a breakthrough in understanding jaw joint morphology in quadrupeds [5][6]. - The second specimen, Camurocondylus lufengensis, from the Late Jurassic, has a simpler dentary condyle structure, supporting the hypothesis that the mammalian dentary condyle originated from the posterior end of the dentary ridge, filling a morphological gap in the transition from early theriodonts to early mammaliaforms [6][7]. Group 2: Evolutionary Implications - The diverse joint structures indicate repeated evolutionary experiments in advanced theriodonts, with secondary jaw joints arising independently multiple times, while the weight-bearing dentary-squamosal joint is a synapomorphic trait of mammaliamorphs [7]. - Factors such as size reduction, mandibular muscle reorganization, feeding ecology, and masticatory behavior are suggested to have influenced this evolutionary transition, emphasizing the role of ecological pressures and developmental flexibility in shaping jaw joint evolution [7]. - A concurrent article in Nature discusses unexpected bone connections in ancient mammalian ancestors, providing insights into how structural innovations in evolution can overcome functional limitations, thus offering a window into vertebrate morphological adaptive evolution [7].