Fossils document evolutionary changes of jaw joint to mammalian middle ear

• 成果类型: Article
• 署名作者: Mao, Fangyuan; Zhang, Chi; Ren, Jicheng; Wang, Tao; Wang, Guofu; Zhang, Fakui; Rich, Thomas; Vickers-Rich, Patricia; Meng, Jin
• 署名单位: Chinese Academy of Sciences; Institute of Vertebrate Paleontology & Paleoanthropology, CAS; American Museum of Natural History (AMNH); Monash University; Curtin University; City University of New York (CUNY) System
• 刊物名称: Nature
• ISSN/ISSBN: 0028-3836
• DOI: 10.1038/s41586-024-07235-0
• 发表日期: 2024-04-18
• 关键词: ossified meckels cartilage; diversification; TRANSFORMATION; TRANSITION; docodont; origin

摘要

The dual jaw joint of Morganucodon(1,2) consists of the dentary-squamosal joint laterally and the articular-quadrate one medially. The articular-quadrate joint and its associated post-dentary bones constitute the precursor of the mammalian middle ear. Fossils documenting the transition from such a precursor to the mammalian middle ear are poor, resulting in inconsistent interpretations of this hallmark apparatus in the earliest stage of mammaliaform evolution(1-5). Here we report mandibular middle ears from two Jurassic mammaliaforms: a new morganucodontan-like species and a pseudotribosphenic shuotheriid species(6). The morganucodontan-like species shows many previously unknown post-dentary bone morphologies(1,2) and exhibits features that suggest a loss of load-bearing function in its articular-quadrate joint. The middle ear of the shuotheriid approaches the mammalian condition in that it has features that are suitable for an exclusively auditory function, although the post-dentary bones are still attached to the dentary. With size reduction of the jaw-joint bones, the quadrate shifts medially at different degrees in relation to the articular in the two mammaliaforms. These changes provide evidence of a gradual loss of load-bearing function in the articular-quadrate jaw joint-a prerequisite for the detachment of the post-dentary bones from the dentary(7-12) and the eventual breakdown of the Meckel's cartilage(13-15) during the evolution of mammaliaforms.