Department of Musculoskeletal & Ageing Science, Institute of Life Course & Medical Sciences, University of Liverpool, The William Henry Duncan Building, 6 West Derby Street, Liverpool L7 8TX, UK.
Department of Earth Sciences, The Natural History Museum, Cromwell Road, London SW7 5BD, UK.
Proc Biol Sci. 2023 Feb 8;290(1992):20222435. doi: 10.1098/rspb.2022.2435. Epub 2023 Feb 1.
The secondary evolution of quadrupedality from bipedal ancestry is a rare evolutionary transition in tetrapods yet occurred convergently at least three times within ornithischian dinosaurs. Despite convergently evolving quadrupedal gait, ornithischians exhibited variable anatomy, particularly in the forelimbs, which underwent a major functional change from assisting in foraging and feeding in bipeds to becoming principal weight-bearing components of the locomotor system in quadrupeds. Here, we use three-dimensional multi-body dynamics models to demonstrate quantitatively that different quadrupedal ornithischian clades evolved distinct forelimb musculature, particularly around the shoulder. We find that major differences in glenohumeral abduction-adduction and long axis rotation muscle leverages were key drivers of mechanical disparity, thereby refuting previous hypotheses about functional convergence in major clades. Elbow muscle leverages were also disparate across the major ornithischian lineages, although high elbow extension muscle leverages were convergent between most quadrupeds. Unlike in ornithischian hind limbs, where differences are more closely tied to functional similarity than phylogenetic relatedness, mechanical disparity in ornithischian forelimbs appears to have been shaped primarily by phylogenetic constraints. Differences in ancestral bipedal taxa within each clade may have resulted in disparate ecomorphological constraints on the evolutionary pathways driving divergence in their quadrupedal descendants.
从两足动物祖先进化而来的四足性的二次进化是四足动物中罕见的进化转变，但至少在鸟臀目恐龙中已经发生了三次趋同进化。尽管具有趋同进化的四足步态，鸟臀目恐龙表现出了不同的解剖结构，特别是在前肢，前肢在功能上发生了重大变化，从帮助两足动物觅食和进食的辅助结构转变为四足动物运动系统的主要承重结构。在这里，我们使用三维多体动力学模型定量地证明了不同的四足鸟臀目恐龙类群进化出了不同的前肢肌肉结构，特别是在肩部周围。我们发现，肩肱关节的外展-内收和长轴旋转肌肉杠杆的主要差异是机械差异的关键驱动因素，从而反驳了关于主要类群功能趋同的先前假说。主要鸟臀目谱系的肘部肌肉杠杆也存在差异，尽管大多数四足动物的高肘伸展肌肉杠杆具有趋同特征。与鸟臀目后肢不同，后肢的差异与其功能相似性比与系统发育关系更为密切，鸟臀目前肢的机械差异似乎主要受到系统发育限制的影响。每个类群中祖先两足动物类群的差异可能导致其四足后代在进化途径上的生态形态差异。
