The evolution of modern sharks, skates and rays (Elasmobranchii) is largely enigmatic due to their possession of a labile cartilaginous skeleton; consequently, taxonomic assignment often depends on isolated teeth. Bullhead sharks (Heterodontiformes) are a group of basal neoselachians, thus their remains and relationships are integral to understanding elasmobranch evolution. Herein we fully describe †Paracestracion danieli – a bullhead shark from the Late Jurassic plattenkalks of Eichstätt, Germany (150–154 Ma) – for its inclusion in cladistic analysis (utilizing parsimonious principles) of morphological characters from complete †Paracestracion and Heterodontus fossil specimens as well as extant forms of the latter. The presence of two separate monophyletic clades within Heterodontiformes was confirmed, based on predominantly non‐dental characters, which show a strong divergence in body morphology between †Paracestracion and Heterodontus; the latter possessing a first dorsal fin and pectoral fins that are more anterior and pelvic fins that are more posterior. This study emphasizes the importance of including non‐dental features in heterodontiform systematics (as compared with the use of dental characters alone) and supports the erection of the family †Paracestracionidae. Further, phylogenetic analysis of molecular data from five extant species suggests that crown heterodontiforms arose from a diversification event 42.58 Ma off the west coast of the Americas.

中文翻译：

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bull头鲨（Chondrichthyes，Heterodontiformes）之间的进化关系

现代鲨鱼，滑冰鞋和rays鱼（Elasmobranchii）的进化很大程度上是神秘的，因为它们具有不稳定的软骨骨架。因此，分类分配通常取决于孤立的牙齿。head鲨（Heterodontiformes）是一组新生基底鱼类，因此它们的遗骸和亲缘关系对于理解分支进化是必不可少的。本文中，我们充分描述† Paracestracion danieli –来自德国艾希施泰特侏罗纪晚期白垩纪的公牛鲨（150–154 Ma）–将其包括在完整的③Paracestracion和Heterodontus形态特征的分类分析中（利用简约原理）化石标本以及后者的现存形式。两个单独的单系进化枝内Heterodontiformes存在确认的基础上，主要是非牙科字符，这表明在†之间体形态的强发散Paracestracion和Heterodontus; 后者具有较前的第一背鳍和胸鳍，以及较后的第一骨盆鳍。这项研究强调了将非牙齿特征包括在异齿动物系统中的重要性（与单独使用牙齿特征相比），并支持勃起纲蝇科的建立。此外，对来自五个现存物种的分子数据的系统发育分析表明，冠状异形体是由美洲西海岸外42.58 Ma的多样化事件引起的。