Due to the peculiar combination of dental features characteristic for different squaliform families, the position of the Late Cretaceous genera Protoxynotus and Paraphorosoides within squaliform families has long been controversial. In this study, we revise these genera based on previously known fossil teeth and new dental material. The phylogenetic placement of Protoxynotus and Paraphorosoides among other extant and extinct squaliforms is discussed based on morphological characters combined with DNA sequence data for extant species. Our results suggest that Protoxynotus and Paraphorosoides should be included in the Somniosidae and that Paraphorosoides is a junior synonym of Protoxynotus. New dental material from the Campanian of Germany and the Maastrichtian of Austria enabled the description of a new species Protoxynotus mayrmelnhofi sp. nov. In addition, the evolution and origin of the characteristic squaliform tooth morphology are discussed, indicating that the elongated lower jaw teeth with erected cusp and distinct dignathic heterodonty of Protoxynotus represents a novel functional adaptation in its cutting-clutching type dentition among early squaliform sharks. Furthermore, the depositional environment of the tooth bearing horizons allows for an interpretation of the preferred habitat of this extinct dogfish shark, which exclusively occupied shelf environments of the Boreal- and northern Tethyan realms during the Late Cretaceous.

由于不同鳞状科的牙齿特征的特殊组合，晚白垩世Protoxynotus和Paraphorosoides在鳞状科中的位置一直存在争议。在这项研究中，我们根据先前已知的牙齿化石和新的牙科材料对这些属进行了修改。基于形态特征结合现存物种的 DNA 序列数据，讨论了Protoxynotus和Paraphorosoides在其他现存和灭绝的角鲨目中的系统发育位置。我们的研究结果表明Protoxynotus和Paraphorosoides应包括在 Somniosidae 中，而Paraphorosoides是Protoxynotus 的初级同义词。来自德国坎帕尼亚人和奥地利马斯特里赫特人的新牙科材料使描述新物种Protoxynotus mayrmelnhofi sp.成为可能。十一月 此外，还讨论了特征性角状牙齿形态的演变和起源，表明Protoxynotus的下颌牙齿细长，尖尖直立，具有明显的前牙异齿。代表了早期角鲨的切割咬合型牙列的一种新的功能适应。此外，牙齿轴承层的沉积环境可以解释这种已灭绝的角鲨的首选栖息地，在白垩纪晚期，这种鲨鱼只占据了北方和北部特提斯地区的陆架环境。