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

角龙类是最著名的恐龙分支之一，因为它们的相对丰富性，以及颅骨同源性的显着多样性，例如角和褶边，可以诊断该分支的更多衍生成员。巨人症是角龙进化的一个趋势，伴随着逐渐复杂的进食机制和颅骨表现多样性的进化。异时性，特别是超态性已被认为是角龙进化的主要影响因素，以解释向大体型的进化和晚期个体发育发生的高级形式。同样，进食装置明显的层次复杂性表明，性格整合通过个体发育和系统发育发生了演变。所有这些进化假说都需要对角龙类恐龙的发育和系统发育有详细的了解，但迄今为止，年龄估计受到的约束很弱，无法量化，而且对详细系统发育的严格依赖也有限。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创新方法与基于树的新颖方法相结合，利用成熟的角龙类系统发育来研究异时性和整合。基于代表进化枝多样性的七个骨干类群的良好采样生长系列，以及角龙的详细系统发育，我们将研究相对于生长策略的共性（异时性）发育时间是否存在相关变化，以及性状块是否代表满足系统发育和个体发育限制标准的集成模块。这些定量研究将使我们能够评估先前关于异时性和整合在角龙进化中所发挥的作用的假设。通过提供对个体发育中何时表达突触性的量化理解，这项研究将有助于解决与基于幼年正型型的物种有效性相关的几个分类学困境，并提供对角龙多样性的更准确的理解。更广泛的影响：这项研究代表了对一个著名群体的进化过程的新的综合探索恐龙。这项研究的新颖方法和结果有望广泛应用于群体生物学、发育生物学、宏观进化和进化进化等不同领域，并将通过同行评审期刊、专业会议和专业网站上的演示进行传播。两名研究生和两名本科生将通过该项目接受培训，研究的各个方面将纳入两位 PI 教授的大学课程中。两位 PI 都参与了自然历史博物馆展品的开发，这项研究的部分内容将被纳入两个正在进行的展览项目以及相关的教育网站和项目中。鉴于媒体对恐龙研究的兴趣，毫无疑问将会出现许多向公众传播这项工作成果的机会。

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.