ABSTRACT

Our understanding of Typothorax coccinarum is primarily based on postcranial material, along with a few isolated cranial elements. Here we describe the first complete articulated skull of Typothorax coccinarum from the Owl Rock Member of the Late Triassic Chinle Formation in Petrified Forest National Park. We assessed the relationships and defining synapomorphies for some of the major clades within Aetosauria by using a combination of morphological characters in the cranium of Typothorax coccinarum. Based on the descriptions of skulls from a variety of aetosaur species including Aetosaurus ferratus, Aetosauroides scagliai, Coahomasuchus chathamensis, Neoaetosauroides engaeus, Paratypothorax andressorum, Stagonolepis olenkae, Stenomyti huangae, Scutarx deltatylus, and now Typothorax coccinarum, it is apparent that the two major aetosaurian clades vary in their overall skull morphologies. The stagonolepidoids share a more robust, elongate skull, with varying degrees in the lateral expansion of the premaxillary tips. On the other hand, aetosaurines share an overall shorter, more gracile skull with tapered premaxillae. These new characters are mapped onto a revised phylogenetic tree for the Aetosauria. Historically, aetosaurs were interpreted as being predominantly herbivorous. In recent years, the discovery of new aetosaur cranial material, like that of Neoaetosauroides engaeus and Aetosauroides scagliai, suggested an omnivorous diet for at least some aetosaur taxa. The dentition of Typothorax coccinarum possesses the most strongly developed heterodonty for an aetosaur, therefore challenging the historical interpretation by expanding the range of dentition types within Aetosauria. This supports the more recent hypothesis that aetosaurs exhibited diverse feeding strategies beyond just herbivory.

摘要

我们对球孢杆菌的理解主要基于颅后材料以及一些孤立的颅骨成分。在这里，我们描述了石化森林国家公园中晚三叠世Chinle组的猫头鹰岩石成员的第一个完整的球形鼓耳球孢子虫。我们通过结合鼓膜球头盖骨颅骨的形态特征评估了埃托龙内一些主要进化枝的关系并定义了突触。基于头骨从各种坚蜥目物种，包括的描述坚蜥ferratus，Aetosauroides scagliai，科荷马鳄属chathamensis，Neoaetosauroides engaeus，副正体龙属andressorum，锹鳞龙属olenkae，Stenomyti huangae，Scutarx deltatylus，现在正体龙属coccinarum，很明显，两个主要的甲龙类进化枝的整体头骨形态各不相同。针状类股骨共享一个更坚固，细长的头骨，上颌前尖端的侧向扩张程度不同。另一方面，阿龙龙的头颅整体较短，较柔韧，前颌骨逐渐变细。这些新的字符被映射到修订的Aetosauria的系统发育树上。从历史上看，甲龙被解释为主要是草食性的。近年来，新坚蜥目颅材料的发现，这样的Neoaetosauroides engaeus和Aetosauroides scagliai，建议至少某些类群坚蜥目杂食性饮食。鼓膜球菌的牙列拥有最强烈的甲龙异性，因此通过扩大甲龙内的牙列类型范围来挑战历史解释。这支持了最近的假说，即恐龙不仅具有食草性，还表现出多种饲养策略。