Data from: Comparative limb proportions reveal differential locomotor morphofunctions of alligatoroids and crocodyloids

Although two major clades of crocodylians (Alligatoroidea and Crocodyloidea) were split during the Cretaceous, relatively few morphological and functional differences between them have been known. In addition, interaction of multiple morphofunctional systems that differentiated their ecology has barely been assessed. In this study, we examined the limb proportions of crocodylians to infer the differences of locomotor functions between alligatoroids and crocodyloids, and tested the correlation of locomotor and feeding morphofunctions. Our analyses revealed crocodyloids including Gavialis have relatively long stylopodia (humerus and femur) than alligatoroids, indicating that two groups may differ in locomotor functions. Fossil evidence suggested that alligatoroids have retained short stylopodia since the early stage of their evolution. Furthermore, rostral shape, an indicator of trophic function, is correlated with limb proportions, where slender-snouted piscivorous taxa have relatively long stylopodia and short overall limbs. In combination, trophic and locomotor functions might differently delimit the ecological opportunity of alligatoroids and crocodyloids in the evolution of crocodylians.尽管鳄类（crocodylians）的两大演化支——短吻鳄超科（Alligatoroidea）与鳄超科（Crocodyloidea）——在白垩纪便已发生分化，但目前已知二者间的形态学与功能学差异相对较少。此外，驱动二者生态分化的多套形态功能系统之间的相互作用，迄今几乎未得到系统评估。本研究针对鳄类的肢体比例展开分析，以推断短吻鳄超科与鳄超科之间的运动功能差异，并检验了运动与摄食形态功能之间的相关性。分析结果显示，包括食鱼鳄属（Gavialis）在内的鳄超科类群，其肢体近段（stylopodia，即肱骨与股骨）相较于短吻鳄超科更长，这表明两类群的运动功能或存在差异。化石证据表明，短吻鳄超科自演化早期便保留了较短的肢体近段。此外，作为摄食功能指示指标的吻部形态（rostral shape），与肢体比例存在相关性：吻部细长的食鱼类群（piscivorous taxa）拥有相对更长的肢体近段与更短的整体肢体。综合来看，摄食与运动功能或在鳄类的演化历程中，分别界定了短吻鳄超科与鳄超科类群的生态机遇（ecological opportunity）。