School of Earth and Environmental Sciences, The University of Manchester, Manchester, United Kingdom.
PLoS One. 2020 Feb 5;15(2):e0211173. doi: 10.1371/journal.pone.0211173. eCollection 2020.
Claws are involved in a number of behaviours including locomotion and prey capture, and as a result animals evolve claw morphologies that enable these functions. Past authors have found geometry of the keratinous sheath of the claw to correlate with mode of life for extant birds and squamates; this relationship has frequently been cited to infer lifestyles for Mesozoic theropods including Archaeopteryx. However, many fossil claws lack keratinous sheaths and thus cannot be analysed using current methods. As the ungual phalanx within the claw is more commonly preserved in the fossil record, geometry of this bone may provide a more useful metric for paleontological analysis. In this study, ungual bones of 108 birds and 5 squamates were imaged using X-ray techniques and a relationship was found between curvatures of the ungual bone within the claw of pedal digit III and four modes of life; ground-dwelling, perching, predatory, and scansorial; using linear discriminant analysis with weighted accuracy equal to 0.79. Our model predicts arboreal lifestyles for Archaeopteryx and Microraptor and a predatory ecology for Confuciusornis. These findings demonstrate the utility of our model in answering questions of palaeoecology, the theropod-bird transition, and the evolution of avian flight. Though the metric exhibits a strong correlation with lifestyle, morphospaces for PD-III curvatures overlap and so this metric should be considered alongside additional evidence.
爪参与了许多行为，包括运动和捕食猎物，因此动物进化出了能够实现这些功能的爪形态。过去的作者发现，爪的角蛋白鞘的几何形状与现生鸟类和蜥蜴的生活方式有关；这种关系经常被用来推断包括始祖鸟在内的中生代兽脚亚目恐龙的生活方式。然而，许多化石爪缺乏角蛋白鞘，因此无法使用当前的方法进行分析。由于爪内的指爪趾骨在化石记录中更为常见，因此该骨骼的几何形状可能为古生物学分析提供更有用的指标。在这项研究中，使用 X 射线技术对 108 只鸟类和 5 只蜥蜴的爪趾骨进行了成像，并发现了爪中第三和第四趾的指爪趾骨的曲率与四种生活方式之间的关系：地面生活、栖息、捕食和攀爬；使用线性判别分析，加权准确率等于 0.79。我们的模型预测始祖鸟和小盗龙为树栖生活方式，孔子鸟为捕食生态。这些发现证明了我们的模型在回答古生态学、兽脚亚目-鸟类过渡和鸟类飞行进化等问题方面的有效性。虽然该指标与生活方式有很强的相关性，但 PD-III 曲率的形态空间重叠，因此该指标应与其他证据一起考虑。
