Department of Anatomy, New York Institute of Technology College of Osteopathic Medicine, Northern Boulevard, Old Westbury, New York.
Department of Anatomy, Howard University College of Medicine, 520 W St. NW, Numa Adams Building, Washington, District of Columbia.
Anat Rec (Hoboken). 2020 Feb;303(2):218-234. doi: 10.1002/ar.23997. Epub 2018 Nov 25.
Tetrapod limbs are a key innovation implicated in the evolutionary success of the clade. Although musculoskeletal evolution of the pectoral appendage across the fins-to-limbs transition is fairly well documented, that of the pelvic appendage is much less so. The skeletal elements of the pelvic appendage in some tetrapodomorph fish and the earliest tetrapods are relatively smaller and/or qualitatively less similar to those of crown tetrapods than those of the pectoral appendage. However, comparative and developmental works have suggested that the musculature of the tetrapod forelimb and hindlimb was initially very similar, constituting a "similarity bottleneck" at the fins-to-limbs transition. Here, we used extant phylogenetic bracketing and phylogenetic character optimization to reconstruct pelvic appendicular muscle anatomy in several key taxa spanning the fins-to-limbs and water-to-land transitions. Our results support the hypothesis that transformation of the pelvic appendages from fin-like to limb-like lagged behind that of the pectoral appendages. Compared to similar reconstructions of the pectoral appendages, the pelvic appendages of the earliest tetrapods had fewer muscles, particularly in the distal limb (shank). In addition, our results suggest that the first tetrapods had a greater number of muscle-muscle topological correspondences between the pectoral and pelvic appendages than tetrapodomorph fish had. However, ancestral crown-group tetrapods appear to have had an even greater number of similar muscles (both in terms of number and as a percentage of the total number of muscles), indicating that the main topological similarity bottleneck between the paired appendages may have occurred at the origin of the tetrapod crown group. Anat Rec, 2018. © 2018 Wiley Periodicals, Inc. Anat Rec, 303:218-234, 2020. © 2018 American Association for Anatomy.
四足动物的四肢是该进化枝成功进化的关键创新。虽然胸鳍附肢的肌肉骨骼进化在鳍到肢的过渡中相当有记载，但骨盆附肢的进化却要少得多。一些四足形鱼类和最早的四足动物的骨盆附肢的骨骼元素相对较小和/或与冠群四足动物的骨骼元素质量差异较大，而不是与胸鳍附肢的骨骼元素质量差异较大。然而，比较和发育研究表明，四足动物前肢和后肢的肌肉最初非常相似，在鳍到肢的过渡中构成了“相似瓶颈”。在这里，我们使用现存的系统发育框架和系统发育特征优化来重建跨越鳍到肢和水到陆过渡的几个关键分类群的骨盆附肢肌肉解剖结构。我们的结果支持这样的假设，即骨盆附肢从鳍状到肢状的转变落后于胸鳍附肢的转变。与胸鳍附肢的类似重建相比，最早的四足动物的骨盆附肢肌肉较少，特别是在远端肢体（小腿）。此外，我们的结果表明，与四足形鱼类相比，第一只四足动物的胸鳍和骨盆附肢之间的肌肉-肌肉拓扑对应关系更多。然而，祖先进化冠群四足动物似乎具有更多相似的肌肉（无论是在数量上还是在总肌肉数的百分比上），这表明配对附肢之间的主要拓扑相似瓶颈可能发生在四足动物冠群的起源。解剖记录，2018. © 2018 Wiley Periodicals， Inc. 解剖记录，303：218-234，2020. © 2018 美国解剖学会。
