Claessens Leon P A M, Vickaryous Matthew K
Department of Biology, College of the Holy Cross, One College Street, Worcester, Massachusetts 01610, USA.
J Morphol. 2012 Oct;273(10):1185-98. doi: 10.1002/jmor.20059. Epub 2012 Jul 21.
Unlike most tetrapods, in extant crocodylians the acetabulum is formed by only two of the three skeletal elements that constitute the pelvis, the ilium, and ischium. This peculiar arrangement is further confused by various observations that suggest the crocodylian pelvis initially develops from four skeletal elements: the ilium, ischium, pubis, and a novel element, the prepubis. According to one popular historical hypothesis, in crocodylians (and many extinct archosaurs), the pubis fuses with the ischium during skeletogenesis, leaving the prepubis as a distinct element, albeit one which is excluded from the acetabulum. Whereas the notion of a distinct prepubic element was once a topic of considerable interest, it has never been properly resolved. Here, we combine data gleaned from a developmental series of Alligator mississippiensis embryos, with a revised interpretation of fossil evidence from numerous outgroups to Crocodylia. We demonstrate that the modern crocodylian pelvis is composed of only three elements: the ilium, ischium, and pubis. The reported fourth pelvic element is an unossified portion of the ischium. Interpretations of pelvic skeletal homology have featured prominently in sauropsid systematics, and the unambiguous identification of the crocodylian pubis provides an important contribution to address larger scale evolutionary questions associated with locomotion and respiration.
与大多数四足动物不同，现存的鳄形目动物的髋臼仅由构成骨盆的三块骨骼中的两块形成，即髂骨和坐骨。这种特殊的结构因各种观察结果而更加复杂，这些观察结果表明鳄形目动物的骨盆最初由四块骨骼发育而来：髂骨、坐骨、耻骨和一个新的元素，即耻骨前骨。根据一个流行的历史假说，在鳄形目动物（以及许多已灭绝的主龙类）中，耻骨在骨骼形成过程中与坐骨融合，使耻骨前骨成为一个独特的元素，尽管它被排除在髋臼之外。虽然耻骨前骨这一独特元素的概念曾经是一个备受关注的话题，但从未得到妥善解决。在这里，我们将从密西西比鳄胚胎发育系列中收集的数据，与对鳄形目众多外类群化石证据的修订解释相结合。我们证明现代鳄形目动物的骨盆仅由三块元素组成：髂骨、坐骨和耻骨。报告中的第四块骨盆元素是坐骨的未骨化部分。骨盆骨骼同源性的解释在蜥形纲系统学中一直占据重要地位，鳄形目耻骨的明确鉴定为解决与运动和呼吸相关的更大规模进化问题做出了重要贡献。
