Department of Earth and Environmental Sciences, University of Manchester, Manchester, UK.
Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, USA.
Nat Commun. 2024 Aug 31;15(1):7587. doi: 10.1038/s41467-024-51963-w.
Cetacean reinvasion of the aquatic realm is an iconic ecological transition that led to drastic modifications of the mammalian body plan, especially in the axial skeleton. Relative to the vertebral column of other mammals that is subdivided into numerous anatomical regions, regional boundaries of the cetacean backbone appear obscured. Whether the traditional mammalian regions are present in cetaceans but hard to detect due to anatomical homogenization or if regions have been entirely repatterned remains unresolved. Here we combine a segmented linear regression approach with spectral clustering to quantitatively investigate the number, position, and homology of vertebral regions across 62 species from all major cetacean clades. We propose the Nested Regions hypothesis under which the cetacean backbone is composed of six homologous modules subdivided into six to nine post-cervical regions, with the degree of regionalization dependent on vertebral count and ecology. Compared to terrestrial mammals, the cetacean backbone is less regionalized in the precaudal segment but more regionalized in the caudal segment, indicating repatterning of the vertebral column associated with the transition from limb-powered to axial-driven locomotion.
鲸类重返水域是一个标志性的生态转变，导致了哺乳动物身体计划的剧烈改变，特别是在轴骨骼上。与其他哺乳动物的脊柱被细分为许多解剖区域相比，鲸类脊柱的区域边界似乎模糊不清。传统的哺乳动物区域是否存在于鲸类中，但由于解剖结构的同质化而难以检测，或者区域是否已经完全重新设计，仍然没有得到解决。在这里，我们结合分段线性回归方法和谱聚类，定量研究了来自所有主要鲸类分支的 62 个物种的椎骨区域的数量、位置和同源性。我们提出了嵌套区域假说，根据该假说，鲸类的脊柱由六个同源模块组成，分为六到九个颈椎后区域，区域化程度取决于椎骨数量和生态。与陆地哺乳动物相比，鲸类的前尾椎骨区域的分区程度较低，但尾部区域的分区程度较高，这表明与从肢体驱动到轴向驱动的运动转变相关的脊柱重新设计。
