Evolution and phylogenetic relationships of the early cerapodan dinosaurs

角脚类是一种主要的食草类两足和四足鸟臀目恐龙，在白垩纪统治着陆生食草生态位。在它们的进化史早期，它们分为两大类群，鸟脚亚目（鸭嘴恐龙及其近亲）和边缘头类（有角、有褶边的恐龙和圆顶恐龙）。在分裂之后，这两个群体都辐射并发展了复杂的咀嚼机制和社会结构，使它们具有高度的多样性和丰富性，它们的化石因杰出的材料而闻名。然而，角足类的早期代表是从更多的碎片遗骸中得知的，这阻碍了我们对它们的分类、关系和进化的理解。特别是，许多早期角足类动物的个体发育状况是未知的，它们的碎片化石记录意味着角足类底部的特征转变仍然不清楚。这限制了我们对这些恐龙的巨型食草性和四足性进化的解释。相互竞争的系统发育假说表明，早期角脚类动物的进化关系截然不同，其中鸟脚类动物属于哪一类群仍不清楚。该项目的目的是对所有基底角足类动物进行全面的解剖和系统的评估，并解决系统发育的不确定性，提供一个健全的进化树。这棵树将被用来研究角足类的进化史，重点是古生物地理学，随着时间的推移的多样性，以及主要分化和辐射的时间。重点研究目标包括：(1)解决关键的基底角足类分类问题，重点研究北美晚侏罗世角足类；(2)研究了早白垩世英国大样本分类群的个体发育状况和种群生态学；(3)确定基底角足类相对于鸟脚类和边缘头足类分化的系统发育位置；(4)利用由此产生的假设，探索生物地理和多样性随时间变化的格局。

Cerapodans are a major group of herbivorous bipedal and quadrupedal ornithischian dinosaurs that dominated the terrestrial herbivorous niche during the Cretaceous. Early in their evolutionary history they split into two major groups, the ornithopods (duck-billed dinosaurs and their relatives) and the marginocephalians (horned and frilled dinosaurs and dome-headed dinosaurs). Subsequent to the split both groups radiated and developed complex chewing mechanisms and social structures that allowed them to achieve high diversity and abundance, and their fossils are well-known from outstanding material. However, early representatives of Cerapoda are known from much more fragmentary remains, and this has hindered our understanding of their taxonomy, relationships, and evolution. In particular, the ontogenetic status of many of the early cerapodans is unknown, and their fragmentary fossil record means that character transitions at the base of Cerapoda remain unclear. This has limited our interpretation of the evolution of mega-herbivory and quadrupedality in these dinosaurs. Competing phylogenetic hypotheses indicate radically different evolutionary relationships for early cerapodans, and it remains particularly unclear which taxa are included within Ornithopoda.The aim of this project is to conduct a comprehensive anatomical and systematic evaluation of all basal cerapodans and resolve phylogenetic uncertainties, providing a robust evolutionary tree. This tree will then be used to investigate the evolutionary history of Cerapoda with a focus on palaeobiogeography, diversity through time, and the timings of major divergences and radiations. Key research aims include: (1) resolving the taxonomy of key basal cerapodans, with a particular focus on North American Late Jurassic taxa; (2) examining the ontogenetic status and population ecology in a large sample of Early Cretaceous British taxa; (3) determining the phylogenetic position of basal cerapodans relative to the divergence of Ornithopoda and Marginocephalia; (4) using the resulting hypothesis to explore biogeographic and diversity patterns through time.