ABSTRACT

Ankylosaurs, dinosaurs possessing extensive body armor, were significant components of terrestrial ecosystems from the Middle Jurassic–latest Cretaceous. They diversified during the Early Cretaceous, becoming globally widespread. The Lower Cretaceous Wealden Supergroup (Berriasian–Aptian) of Britain has produced abundant ankylosaur material, with three currently recognized taxa: Hylaeosaurus armatus (Grinstead Clay Formation, West Sussex); Polacanthus foxii (Wessex Formation, Isle of Wight); and Horshamosaurus rudgwickensis (Weald Clay Group, West Sussex). However, these taxa are poorly understood; the initial descriptions of Hylaeosaurus and Polacanthus date from the 1800s and subsequent referrals of specimens have been based largely on provenance rather than morphological comparisons. This has led to uncertainty over the definitions of these taxa and the compositions of their hypodigms. Here, we redescribe the holotypes of Hylaeosaurus and Polacanthus, provide comparisons between these taxa, and use this information to assess the taxonomy of all ankylosaur specimens from the British Wealden Supergroup. We conclude that Hylaeosaurus and Polacanthus are valid, distinct taxa, which can be diagnosed by a combination of autapomorphies and a unique combination of characters. However, in both cases, we restrict their hypodigms to the holotypes. ‘Horshamosaurus rudgwickensis’ is a nomen dubium (an indeterminate nodosaurid dinosaur) and the majority of ankylosaur specimens from the Wealden Supergroup are taxonomically indeterminate. Hylaeosaurus and Polacanthus are separated stratigraphically, with Hylaeosaurus from the Valanginian of the Weald Sub-basin and Polacanthus from the Barremian of the Wessex Sub-basin. This separation supports the hypothesis of distinct lower and upper dinosaur faunas in the Wealden Supergroup of Britain.

摘要

甲龙具有广泛的防弹衣，是中侏罗纪至最新白垩纪陆地生态系统的重要组成部分。他们在白垩纪早期就开始多样化，并在全球范围内广泛传播。英国的下白垩统Wealden超级群（Berriasian–Aptian）产生了丰富的甲龙材料，其中有三种目前公认的分类群：Hylaeosaurus armatus（西萨塞克斯郡格林斯特德粘土地层）；Polacanthus foxii（怀特岛的Wessex组）；和Horshamosaurus rudgwickensis（西萨塞克斯郡Weald Clay集团）。但是，对这些分类单元的了解很少。Hylaeosaurus和Polacanthus的初始描述从1800年代开始，随后的标本移交很大程度上是基于出处而不是形态上的比较。这导致对这些分类单元的定义及其假想范式的组成存在不确定性。在这里，我们重新描述了Hylaeosaurus和Polacanthus的同型，提供了这些类群之间的比较，并使用此信息来评估来自英国Wealden Supergroup的所有腕龙标本的分类。我们得出的结论是，Hylaeosaurus和Polacanthus是有效的，截然不同的类群，可以通过自然词型组合和字符的独特组合来诊断。但是，在这两种情况下，我们都将它们的假设仅限于整型。“ Horshamosaurus rudgwickensis”是nobo dubium（不确定的十二指肠恐龙），Wealden Supergroup的大多数甲龙标本在分类学上都是不确定的。Hylaeosaurus和Polacanthus在地层上是分开的，来自Weald子盆地的Valanginian的Hylaeosaurus和来自Wessex子盆地的Barremian的Polacanthus。这种分离支持了英国Wealden超群中不同的上下恐龙动物群的假设。