A Revision of Sphenosuchus acutus Haughton, a Crocodylomorph Reptile from the Elliot Formation (Late Triassic or Early Jurassic) of South Africa
A Revision of Sphenosuchus acutus Haughton, a Crocodylomorph Reptile from the Elliot Formation (Late Triassic or Early Jurassic) of South Africa
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尖鳄霍顿 (Sphenosuchus acutus Haughton) 的修订版，一种来自南非埃利奥特组（晚三叠世或早侏罗世）的鳄形爬行动物
DOI：
10.1098/rstb.1990.0185
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发表时间：
1990
期刊：
影响因子：
--
通讯作者：
A. D. Walker
中科院分区：
文献类型：
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作者：
A. D. Walker
详细描述了Sphosuchus正型的骨学特征。头骨，特别是脑壳，保存完好，并显示出丰富的解剖细节。Sphosuchus是早期最大的鳄形动物之一，头骨长192 mm，估计全长1.4m。正方形的初级头部与隆突和鳞片相接，而不与反面(或侧翼)相接；正方形和翼状突不与脑壳融合，八翼突关节是自由的。脑壳和其他一些头盖骨被充气。耳囊为鳄鱼状，但包膜下支撑物(骨化的包膜下突起)不包裹迷走神经或颈内动脉。肩胛骨是三角形的；喙突有一个很长的后腹延伸，被认为与一个大的锁骨间隙牢固地连接在一起。锁骨缺失。第1跖骨缩小，第2、IV跖骨对称，长度最长的是III。现场出现了一对背部盾牌。Sphosuchus被认为是草食性和肉食性的。比较了Sphosuchus头骨上的气动间隙与现代鳄鱼和鸟类的气动间隙，并讨论了同源性。在鳄鱼头骨中发现的主要洞穴的代表存在于Sphosuchus的头骨中，在某些情况下处于不太清楚的状态。另一方面，Sphosuchus头骨中的某些气动空间在现代鳄鱼中并不存在，但类似于鸟类头骨中的空洞。颈内动脉和腓动脉的走行被重建；后者被认为像现代形式一样穿过方后孔、颞管和颞前孔。文中还讨论了鳄骨动脉的位置问题。认为动脉的封闭是方头向前移动的结果，导致了颞管的形成。详细比较了Sphosuchus的耳壳与现代鳄鱼和鸟类的耳囊，它们非常相似。在始祖龙耳壳结构的变化，使鳄鱼或鸟类的情况，从原始形式，如真帕里克虫，概述。幼年的Sphosuchus的头骨被认为是动态的，方形的链状花柱。鳄鱼正方形近端的部分是有区别的；特别是，真的头部与前背突是不同的。虽然在现代鳄鱼中非常缩小，但真正的头部与Sphosuchus处于相同的形态位置；与侧骨的接触不是通过头部的进一步向前移动，而是通过骨骼上部的屈膝。前齿突被认为是前外侧突起向背侧移动的结果，与齿状突的突起有些相似。这一变化也是鳄形动物颈四头肌伸长的原因。讨论了鳄鱼形目的正确性。结论是，鳄鱼形态进化的最重要步骤，特别是在头骨中，发生在蝶形目动物中，因此它们应该与原脊椎动物和更高级的鳄鱼纲属于同一分类群，而不是与齿状目动物。
A detailed description is given of the osteology of the holotype of Sphenosuchus. The skull, particularly the braincase, is excellently preserved and shows a wealth of anatomical detail. Sphenosuchus was one of the largest of the early crocodylomorphs, with a skull length of 192 mm and an estimated total length of 1.4 m. The primary head of the quadrate meets the prootic and squamosal but not the opisthotic (or laterosphenoid); quadrate and pterygoid are not fused to the braincase and the basipterygoid articulation is free. The braincase and some other skull bones are pneumatized. The otic capsule is crocodilian but the subcapsular buttress (ossified subcapsular process) does not enclose the vagus nerve or the internal carotid artery. The scapula blade is triangular; the coracoid has a long posteroventral extension which is thought to have articulated firmly with a large interclavicle. Clavicles were absent. Metatarsal I is reduced; metatarsals II and IV are symmetrical about III, which is longest. A paired series of dorsal scutes was present. Sphenosuchus is considered to have been cursorial and carnivorous. Comparison is made between the pneumatic spaces in the Sphenosuchus skull and those of modern crocodiles and birds, and homologies are discussed. Representatives of the main cavities found in the crocodilian skull are present in the skull of Sphenosuchus, in some cases in a less clearly defined state. On the other hand, certain pneumatic spaces in the Sphenosuchus skull are not found in the modern crocodile but resemble cavities in the bird skull. The courses of the internal carotid and stapedial arteries are reconstructed; the latter is considered to have passed through the postquadrate foramen, temporal canal and anterior temporal foramen as it does in modern forms. The problem of the position of the stapedial artery in the crocodile is discussed. It is believed that enclosure of the artery took place as a result of the forward migration of the quadrate head, leading to the formation of a temporal canal. Detailed comparisons are made between the otic capsule of Sphenosuchus and those of modern crocodiles and birds, which it closely resembles. Changes in otic capsule structure in archosaurs to give the crocodilian or bird condition, starting from a primitive form like Euparkeria, are outlined. The skull is believed to have been kinetic, and the quadrate streptostylic, in the juvenile Sphenosuchus. The parts of the proximal end of the crocodilian quadrate are differentiated; in particular, the \`true' head is distinguished from the anterodorsal process. Although very reduced in the modern crocodile, the \`true' head is in the same morphological position as in Sphenosuchus; contact with the laterosphenoid has been brought about, not by further forward movement of the head, but by geniculation of the upper portion of the bone. The anterodorsal process is considered to have arisen as a result of the dorsal migration of an anterolateral projection somewhat similar to that of the thecodontian Stagonolepis. This change was also responsible for the elongation of the quadratojugal in crocodylomorphs. The validity of the order Crocodylomorpha is discussed. It is concluded that the most important steps in crocodylomorph evolution, particularly in the skull, had taken place in sphenosuchians, hence they should be included in the same taxon as protosuchians and more advanced crocodilians, rather than with thecodontians.