Grogan Eileen D, Lund Richard, Didier Dominique
Biology Department, St. Joseph's University, Philadelphia, Pennsylvania.
Department of Environmental Studies, Adelphi University, Garden City, New York.
J Morphol. 1999 Jan;239(1):45-59. doi: 10.1002/(SICI)1097-4687(199901)239:1<45::AID-JMOR3>3.0.CO;2-S.
Anatomical delineation of the holocephalan palatoquadrate has proven to be difficult and, so, has been an extensively debated topic as it relates to the evolutionary derivation of jaws, modes of jaw suspension, and the interrelationships of the hondrichthyes (Elasmobranchii and Holocephali). Embryological analyses of the chimaerid jaw and cranium are presented to provide an anatomical description of the palatoquadrate in modern chimaerids. The palatoquadrate fuses, anteriorly, to the nasal capsule early in development. This marks the first point of contact between the mandibular arch and cranium. Orbitonasal canal foramina delineate the dorsal palatoquadrate margin. The posteriormost margin is marked by fusion of the upper jaw with trabecular and parachordal cartilages in the region of the efferent eudobranchial artery foramen and by a suborbitally positioned basitrabecular cartilage. This basitrabecula generates a subocular shelf as it fuses medially to the parachordal cartilage and posteriorly to the postorbital wall and cranial otic process. The results of these analyses are related to morphological studies of Paleozoic chondrichthyan fishes, particularly the autodiastylic paraselachians that represent morphological intermediates to selachians and holocephalans. The paraselachian basitrabecular, which was mechanically fundamental to stabilizing the free autodiastylic upper jaw and a hyoid operculum, is shown to correlate with the suborbital basitrabecular of today's chimaerids. Further analyses of both extant and fossil data permit us to conclude that the primordial chondrichthyan palatoquadrate did not extend posteriorly to include a palatoquadrate-derived otic process. Rather, the posteriormost extent of this element is primitively found within the limits of the orbit and is demarcated by the highly conserved basitrabecular element. The collective analyses support autodiastyly as the ancestral condition from which all fundamental suspensorial states are derived. J. Morphol. 239:45-59, 1999. © 1999 Wiley-Liss, Inc.
全头类腭方骨的解剖学界定已被证明是困难的，因此，它一直是一个广泛争论的话题，因为它涉及颌骨的进化起源、颌骨悬系模式以及板鳃亚纲鱼类（鲨总目和全头亚纲）的相互关系。本文展示了银鲛颌骨和颅骨的胚胎学分析，以提供现代银鲛腭方骨的解剖学描述。腭方骨在发育早期向前与鼻囊融合。这标志着下颌弓与颅骨的第一个接触点。眶鼻管孔划定了腭方骨的背侧边缘。最靠后的边缘以上颌与传出真鳃动脉孔区域的小梁软骨和副索软骨融合以及眶下位置的基小梁软骨为标志。当这个基小梁向内侧与副索软骨融合并向后与眶后壁和颅骨耳突融合时，会形成一个眶下架。这些分析结果与古生代软骨鱼类的形态学研究相关，特别是代表鲨类和全头类形态中间类型的自接型副鲨类。副鲨类的基小梁在机械上对于稳定自由的自接型上颌骨和舌鳃盖至关重要，它与现今银鲛的眶下基小梁相关。对现存和化石数据的进一步分析使我们能够得出结论，原始软骨鱼类的腭方骨在后方并不延伸以包括一个源自腭方骨的耳突。相反，该元素的最靠后范围最初位于眼眶范围内，并由高度保守的基小梁元素划定界限。这些综合分析支持自接型是所有基本悬系状态所衍生的祖先状态。《形态学杂志》239:45 - 59，1999年。© 1999威利 - 利斯公司。
