2019年11月27日，《自然》在线发表了中国科学院古脊椎动物与古人类研究所王元青等研究人员的最新发现。通过分析白垩纪化石，他们揭示了哺乳动物中耳演化的新模式。

研究人员表示，哺乳动物中耳的演化被认为是“重演”的一个例子，即该物种目前的胚胎发育反映了其进化历史的理论。来自发育生物学和古生物学的积累数据表明，在哺乳动物中，齿后牙颌元件向颅耳骨的转化发生了数次。此外，保存完好的化石还揭示了哺乳动物中耳进化的过渡阶段。但是，关于中耳进化的问题仍然存在，例如，在不同的哺乳动物形式中，齿后单元如何以及为什么从齿骨中完全脱离。

研究人员发现在盖氏热河俊兽标本中保存的哺乳动物中耳，其完整的牙齿后元素被很好地保存并且与牙齿骨骼分离。该标本揭示了上颌下颌骨从一个独立的元素到中耳锤骨的一部分的转变，以及在柱状骨和扁平骨之间的接触受限。研究人员认为，锤骨-砧骨关节在哺乳动物形式中是二分体的，两根骨头以邻接或互锁的方式连接，反映了齿骨-鳞骨关节的进化差异。在系统发育分析中，像这样的标本在其他变种动物中确定的哺乳动物中耳的采集独立于单孔类等。这些研究结果表明，在同种异体动物中，初级和次级颌关节的共同进化是一种进化适应，从而以独特的咀嚼方式进食。

附：英文原文

Title: Cretaceous fossil reveals a new pattern in mammalian middle ear evolution

Author: Haibing Wang, Jin Meng, Yuanqing Wang

Issue&Volume: 2019-11-27

Abstract: The evolution of the mammalian middle ear is thought to provide an example of recapitulationthe theory that the present embryological development of a species reflects its evolutionary history. Accumulating data from both developmental biology and palaeontology have suggested that the transformation of post-dentary jaw elements into cranial ear bones occurred several times in mammals1,2. In addition, well-preserved fossils have revealed transitional stages in the evolution of the mammalian middle ear1,3,4. But questions remain concerning middle-ear evolution, such as how and why the post-dentary unit became completely detached from the dentary bone in different clades of mammaliaforms. Here we report a definitive mammalian middle ear preserved in an eobaatarid multituberculate mammal, with complete post-dentary elements that are well-preserved and detached from the dentary bones. The specimen reveals the transformation of the surangular jaw bone from an independent element into part of the malleus of the middle ear, and the presence of a restricted contact between the columelliform stapes and the flat incus. We propose that the malleusincus joint is dichotomic in mammaliaforms, with the two bones connecting in either an abutting or an interlocking arrangement, reflecting the evolutionary divergence of the dentarysquamosal joint4. In our phylogenetic analysis, acquisition of the definitive mammalian middle ear in allotherians such as this specimen was independent of that in monotremes and therians. Our findings suggest that the co-evolution of the primary and secondary jaw joints in allotherians was an evolutionary adaptation allowing feeding with unique palinal (longitudinal and backwards) chewing. Thus, the evolution of the allotherian auditory apparatus was probably triggered by the functional requirements of the feeding apparatus. The mammalian middle ear is thought to have evolved independently several times, and a specimen of the new species Jeholbaatar kielanae provides support for the idea, with evolution of the chewing apparatus perhaps driving migration of the auditory bones.

DOI: 10.1038/s41586-019-1792-0

Source:https://www.nature.com/articles/s41586-019-1792-0