Abstract The horned dinosaur genus Torosaurus has a challenging history, relating both to its geographic distribution and taxonomy. Whereas Torosaurus has been reported from Upper Maastrichtian deposits in Canada, which would mark the northernmost range of the genus, recent work has questioned the generic identity of the implicated material, which primarily consists of a pair of cranial frills. Perhaps more problematically, the validity of the genus itself has been a subject of recent debate, with some arguing that Torosaurus is simply a skeletally mature growth form of the contemporaneous Triceratops. In this study, we describe and illustrate the relevant frill material from Canada, and determine that it is most plausibly attributable to the Torosaurus morph. Moreover, we apply for the first time osteohistological sampling to some postcranial material associated with one of the frills, and find that the animal was still growing at the time of death. This finding, in addition to other considerations presented here, leads us to conclude that Torosaurus is a valid genus, and is not simply a mature growth form of Triceratops.

中文翻译：

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加拿大角龙（鸟臀目：角龙科）的记录及其分类学意义

摘要 角恐龙属Torosaurus 具有挑战性的历史，这与它的地理分布和分类有关。尽管据报道，在加拿大上马斯特里赫特的矿床中发现了牛角龙，这将标志着该属的最北端，但最近的工作质疑了相关材料的一般身份，该材料主要由一对颅骨褶边组成。也许更成问题的是，该属本身的有效性一直是最近争论的主题，一些人认为，牛角龙只是同时代三角龙骨骼成熟的生长形式。在这项研究中，我们描述并说明了来自加拿大的相关褶边材料，并确定它最合理地归因于角龙变形。而且，我们首次对与其中一个褶边相关的颅后材料进行了骨组织学取样，发现该动物在死亡时仍在生长。除了这里提出的其他考虑因素外，这一发现使我们得出结论，牛角龙是一个有效的属，而不仅仅是三角龙的成熟生长形式。