Mead Amelia, Funston Gregory, Brusatte Stephen
Department of Geology and of Geophysics, School of GeoSciences, University of Edinburgh, Edinburgh, UK.
Royal Ontario Museum, Toronto, Ontario, Canada.
R Soc Open Sci. 2025 Mar 26;12(3):242114. doi: 10.1098/rsos.242114. eCollection 2025 Mar.
Theropod forelimbs exhibit wide morphological disparity, from the elongated wings of birds to the diminutive arms of . A wealth of work has sought to understand the evolution of bird flight via arm elongation, but despite widespread occurrences of forelimb reduction and digit loss throughout theropod dinosaurs, the evolutionary drivers behind these patterns are poorly understood. Previous studies demonstrate broad allometric trends that can account for some instances of forelimb reduction, but the repeated loss of digits, and their hypothesized link to forelimb shortening, has received less attention. Here, we evaluate evolutionary associations between digit loss and forelimb reduction in an iconic and data-rich theropod clade, Oviraptorosauria. Unexpectedly, we find that the evolution of digit III and the rest of the forelimb are decoupled. Support for different evolutionary models and a lower phylogenetic signal in digit III than the rest of the forelimb suggests these segments were subject to different evolutionary processes leading to independent morphological change. Oviraptorosaurs exhibit four distinct forelimb morphotypes, but these do not exactly correspond to patterns of dietary niche partitioning. Overall, forelimb evolution in oviraptorosaurs is more complex than anticipated, potentially as a result of an evolutionary radiation they underwent in the Late Cretaceous.
兽脚亚目恐龙的前肢形态差异很大，从鸟类细长的翅膀到……短小的手臂。大量研究试图通过手臂伸长来理解鸟类飞行的进化，但尽管在兽脚亚目恐龙中普遍存在前肢缩短和指骨缺失的情况，但这些模式背后的进化驱动因素却知之甚少。先前的研究表明，广泛的异速生长趋势可以解释一些前肢缩短的情况，但指骨的反复缺失以及它们与前肢缩短的假设联系却较少受到关注。在这里，我们评估了一个具有标志性且数据丰富的兽脚亚目分支——窃蛋龙类中，指骨缺失与前肢缩短之间的进化关联。出乎意料的是，我们发现第三指的进化与前肢的其他部分是解耦的。对不同进化模型的支持以及第三指比前肢其他部分更低的系统发育信号表明，这些部分经历了不同的进化过程，导致了独立的形态变化。窃蛋龙表现出四种不同的前肢形态类型，但这些并不完全对应于饮食生态位划分模式。总体而言，窃蛋龙的前肢进化比预期的更为复杂，这可能是它们在白垩纪晚期经历进化辐射的结果。
