Claeson Kerin M
Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, Austin, Texas 78712, USA.
J Morphol. 2011 Dec;272(12):1444-63. doi: 10.1002/jmor.10996. Epub 2011 Jul 20.
Comparison of embryonic specimens with juvenile and mature specimens of other skates indicates that the relative developmental sequence of events is maintained among several taxa within larger clades. However, there is a fundamental difference between the pattern of chondrification and the pattern of calcification in skates. Early in ontogeny a short synarcual surrounds the first free vertebral centrum. Additional neural arch segments are incorporated from anterior to posterior and the relative length of the synarcual cartilage to total length of the body normalizes early. A secondary direction of chondrification, from ventral to dorsal, is also present. Juveniles and subadults show that synarcual calcification is relatively late compared to the calcification of other regions of the skeleton and proceeds from lateral to medial. Comparison with extinct taxa also indicates that there is a decrease in vertebral centrum involvement with the synarcual cartilage over the evolutionary history of the clade. Results from exploratory analyses of morphospace and taxonomy reveal that phylogeny explains part, but not all, of the data on the synarcual in Rajidae. There is evidence of individual and ontogenetic variation among all species of skates examined, however, phylogenetically informative variation prevails. Comparison with other batoids demonstrates a trend where the number of vertebral centra flanked by the synarcual cartilage decreases among more derived taxa indicating a high degree of convergent morphology among batoids with potential functional significance.
将鳐鱼胚胎标本与其他鳐类的幼年和成年标本进行比较表明，在更大分支中的几个分类群中，事件的相对发育顺序得以维持。然而，鳐鱼的软骨化模式和钙化模式之间存在根本差异。在个体发育早期，一个短的联合弧围绕着第一个游离的椎体中心。额外的神经弓节段从前向后并入，联合弧软骨相对于身体总长度的比例在早期就趋于正常。还存在从腹侧到背侧的第二个软骨化方向。幼年和亚成体显示，与骨骼其他区域的钙化相比，联合弧钙化相对较晚，且从外侧向内侧进行。与已灭绝分类群进行比较还表明，在该分支的进化历史中，椎体中心与联合弧软骨的关联有所减少。形态空间和分类学的探索性分析结果表明，系统发育解释了鳐科联合弧数据的一部分，但并非全部。在所研究的所有鳐类物种中都有个体和个体发育变异的证据，然而，具有系统发育信息的变异占主导。与其他鳐形目鱼类进行比较显示出一种趋势，即在更进化的分类群中，联合弧软骨两侧的椎体中心数量减少，这表明鳐形目鱼类之间存在高度趋同的形态，可能具有功能意义。
