Werneburg Ingmar, Bronzati Mario
Paläontologische Sammlung, Senckenberg Centre for Human Evolution and Palaeoenvironment (SHEP) an der Universität Tübingen, Tübingen, Germany.
Fachbereich Geowissenschaften, Universität Tübingen, Tübingen, Germany.
J Anat. 2025 Mar;246(3):402-414. doi: 10.1111/joa.14105. Epub 2024 Sep 19.
Whereas mammals are characterized by the presence of three middle ear ossicles, reptiles have only one, the columella (stapes). Nevertheless, there is a great diversity of columellar anatomy among sauropsids, especially in the unique and cartilaginous "extracolumella"-portion. Molecular studies revealed the "columella" of chicken and quails to be formed within the second pharyngeal arch, although conflicting evidence exists for the columellar footplate and distal parts of the columella in these birds. We studied columellar development in four turtles, one lizard, and one caiman species and argue, using early blastematous stages, that, distally, the so-called "extracolumella" in turtles is mainly of quadrate, that is, first pharyngeal arch origin. Differently, the dorsal aspect of the "extracolumella" of the lizard and a part of the "dorsal columella process" of the caiman are likely quadrate-derived. This indicates only a partial homology of the distal columellar compartments among reptiles. Moreover, we observed in most species that, at early stages, the footplate differentiates from the otic capsule, which confirms widespread experimental findings of mesodermal cells contributing to the proximal part of the columella. We provide a hypothetical framework for the changes in the columella and quadrate morphology in reptilian evolution. Originally, as evidenced by the fossil record, the columella served as a stabilizing brace between the quadrate and braincase. Associated with changes in the feeding mode of late Permian taxa, the quadrate was integrated along the stress flows from biting, and in early development part of the quadrate differentiated to differently contribute to the distal part of the "columella-complex," which now contacts the tympanic membrane. In addition, part of the original otic capsule contributes to the footplate of the mobile columella, providing a connection with the inner ear.
哺乳动物的特征是有三块中耳听小骨，而爬行动物只有一块，即耳柱骨（镫骨）。然而，蜥形纲动物的耳柱骨解剖结构存在很大差异，尤其是在独特的软骨“额外耳柱骨”部分。分子研究表明，鸡和鹌鹑的“耳柱骨”是在第二咽弓内形成的，尽管关于这些鸟类耳柱骨脚板和耳柱骨远端部分存在相互矛盾的证据。我们研究了四种龟类、一种蜥蜴和一种凯门鳄的耳柱骨发育情况，并利用早期芽基阶段论证，在远端，龟类所谓的“额外耳柱骨”主要起源于方骨，即第一咽弓。不同的是，蜥蜴“额外耳柱骨”的背侧部分和凯门鳄“背侧耳柱骨突”的一部分可能起源于方骨。这表明爬行动物远端耳柱骨隔室仅存在部分同源性。此外，我们在大多数物种中观察到，在早期阶段，脚板从耳囊分化而来，这证实了中胚层细胞参与耳柱骨近端部分形成的广泛实验结果。我们为爬行动物进化过程中耳柱骨和方骨形态的变化提供了一个假设框架。最初，化石记录表明，耳柱骨是方骨和脑壳之间的稳定支撑。随着二叠纪晚期类群摄食方式的变化，方骨沿着咬合力的应力流整合，在早期发育过程中，方骨的一部分分化，以不同方式对现在与鼓膜接触的“耳柱骨复合体”远端部分做出贡献。此外，原始耳囊的一部分形成了可活动耳柱骨的脚板，与内耳建立了连接。
