The origin of crocodilian locomotion
The origin of crocodilian locomotion
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鳄鱼运动的起源
作者：
J. Parrish
最早的鳄鳄类和它们最近的亲戚哈洛普斯和“楔鳄类”的跗骨、后肢和骨盆的形态表明，这些动物已经适应了直立的姿势。在具有与鳄鱼正常的跗骨的主龙类中，直立步态的明显同源适应的广泛分布表明，这些结构对于这个群体来说是近形的，包括Aetosauria，“rauisuchians”，“sphenosuchians”，Hallopus和Crocodylia。直立姿势的适应在近端跗骨（黄芪和跟骨）的结构中表现得最为清楚。这一论点的一个重要含义是，最原始的鳄形类，包括“原鳄类”鳄鱼，“楔鳄类”，和Hallopus，有一个直立的立场和步态。现代鳄鱼在游泳和进入水中时所使用的伸展姿势和相关步态可以被视为对水生生物的次级适应。沉积环境和“sphenosuchian”和“protosuchian”鳄鱼的区系协会是一致的，主要是陆地生活习惯。现存的鳄鱼有两种类型的步伐循环，伸展和直立;伸展的模式被叠加在推断的祖先“高步行”和幼年鳄鱼有时使用的疾驰上。
The morphology of the tarsi, hindlimbs, and pelves of the earliest crocodilians and their nearest relatives, Hallopus and the “sphenosuchians,” indicates that these animals had adaptations for erect posture. The widespread distribution of apparently homologous adaptations for erect gait among the archosaurs with crocodile-normal tarsi suggests that those structures are plesiomorphic for this group, which comprises the Aetosauria, “rauisuchians,” “sphenosuchians,” Hallopus, and the Crocodylia. Adaptations for erect posture are seen most clearly in the structure of the proximal tarsus (astragalus and calcaneum). An important implication of this argument is that the most primitive crocodylomorphs, comprising the “protosuchian” crocodiles, the “sphenosuchians,” and Hallopus, had an erect stance and gait. The sprawling stance and associated gait used by modern crocodilians during swimming and upon entering the water can be viewed as secondary adaptations to an aquatic existence. The environments of deposition and faunal associations of “sphenosuchians” and “protosuchian” crocodiles are consistent with primarily terrestrial habits. Living crocodilians have two types of step cycles, sprawling and erect; the sprawling pattern is overprinted onto the inferred ancestral “high-walk,” and onto the gallop sometimes used by juvenile crocodilians.