Collaborative Research: The Role of Development and Life History Traits in the Evolution of Ceratopsian Dinosaurs

角鼻龙是最著名的恐龙分支之一，因为它们的数量相对丰富，而且颅骨突触的显著多样性，如角和褶边，可以诊断出该分支的更多衍生成员。巨人症是角龙进化的一个趋势，伴随着越来越复杂的进食机制和颅骨显示多样性的进化。异时性，特别是变态被认为是角鼻虫进化的主要影响因素，以解释向大尺寸和晚期个体发育的进化。同样，进食装置的明显层次复杂性表明，通过个体发生和系统发生的特征整合进化。所有这些进化假说都需要对角龙的发育和系统发生有详细的了解，但到目前为止，对恐龙年龄的估计还没有得到很好的约束和量化，严格依赖详细的系统发生也很有限。在这项研究中，一种基于组织学切片和发育质量外推的化石发育分期的创新方法与基于树的新方法相结合，利用成熟的角鼻虫系统发育研究异时性和整合性。基于代表进化分支多样性的7个骨干分类群的良好样本生长序列，以及角鼻虫的详细系统发育，我们将研究相对于生长策略，突触发育时间（异时性）是否存在相关的变化，以及特征块是否代表满足系统发育和个体发育约束标准的集成模块。这些定量研究将使我们能够评估以前关于异时性和整合在角龙进化中所起作用的假设。通过对个体发育中突触形态何时表达的量化理解，本研究将有助于解决与基于幼崽全型的物种有效性相关的几个分类学难题，并提供对角龙多样性的更准确理解。更广泛的影响：这项研究代表了对一个知名恐龙群进化过程的新的综合探索。这项研究的新方法和结果有望广泛应用于种群生物学、发育生物学、宏观进化和进化等领域，并将通过同行评议的期刊、专业会议和专业网站进行传播。通过该项目将培养两名研究生和两名本科生，研究的各个方面将被纳入两位pi教授的大学课程。这两个pi都参与了自然历史博物馆展览的开发，部分研究将纳入两个正在进行的展览项目，以及相关的教育网站和节目。鉴于媒体对恐龙研究的兴趣，无疑会有许多机会向公众传播这项工作的结果。

Ceratopsians are among the best known of dinosaur clades due to their relative abundance, and the remarkable diversity of cranial synapomorphies such as horns and frills that diagnose more derived members of the clade. Gigantism is a trend in ceratopsian evolution that is accompanied by the evolution of progressively more complex feeding mechanisms and cranial display diversity. Heterochrony, and in particular peramorphosis have been proposed as major influences in ceratopsian evolution to explain the evolution towards large size and late ontogenetic genesis of the display in advanced forms. Likewise, the apparent hierarchical complexity of the feeding apparatus suggests an evolution of character integration through both ontogeny and phylogeny. All of these evolutionary hypotheses require detailed knowledge of both the development and phylogeny of ceratopsian dinosaurs, but so far age estimates have been poorly constrained and non-quantified and rigorous reliance on detailed phylogenies limited.In this study, an innovative approach to developmentally staging fossils based onhistological sectioning and Developmental Mass extrapolation is combined with novel tree-based methods toward studying heterochrony and integration using a well established phylogeny of Ceratopsia. Based on well-sampled growth series of seven backbone taxa representing the diversity of the clade, and a detailed phylogeny of ceratopsians, we will examine whether there are correlated shifts in developmental timing of synapomorphies (heterochrony) relative to growth strategies, and also if blocks of characters represent integrated modules that fulfill criteria for being phylogenetically and ontogenetically constrained. These quantitative studies will allow us to evaluate previous hypotheses on the role heterochrony and integration have played in ceratopsian evolution.By providing a quantified understanding of when in ontogeny synapomorpies are expressed this research will help to resolve several taxonomic quandaries related to the validity of species based on juvenile holotypes and provide a more accurate understanding of ceratopsian diversity.Broader Impact: This research represents a new integrative exploration of evolutionary processes in a well-known group of dinosaurs. The novel methods and the results of this research promise to be widely applicable to fields as diverse as population biology, developmental biology, macroevolution and evo-devo, and will be disseminated through peer -reviewed journals, presentations at professional meetings and professional websites. Two graduate and two undergraduate students will be trained through this project, and aspects of the research will be incorporated into university courses taught by both PIs. Both PIs are involved with developing exhibits for natural history museum, and parts of this research will be incorporated into two ongoing exhibit projects, and associated educational web-sites and programming. Given the media interest in dinosaurresearch, many opportunities to disseminate results of this work to the public will no doubt arise.