Doctoral Dissertation Research: Unraveling primate supraordinal relationships: Insights from plesiadapiform cranial morphology

解开灵长类动物（人类所属的哺乳动物群体）起源的核心是蛇适应形（plesiadapiform）的化石，它们是由灵长类动物和密切相关的哺乳动物组成的一个已灭绝的群体（原始祖目）的成员。长期以来，人们一直认为一些蛇颈类动物与一些当代灵长类动物具有共同的特征，但使用更新的、最先进的方法对蛇颈类动物进行进一步分析，可以进一步促进我们对灵长类动物起源的理解。本博士论文项目采用高分辨率x射线微计算机断层扫描（μCT）等方法，分析和比较了蛇颈适应兽与现存灵长类动物和其他胎盘哺乳动物的颅骨解剖结构。在新的进化树的背景下，产生了详细的颅骨比较，可以增加对蛇适应动物，现存灵长类动物和其他原始哺乳动物之间进化关系的评估。该项目还通过指导、公共科学参与活动和数据共享提供了许多推广机会。该项目的见解可以纳入促进STEM中代表性不足群体参与的计划。研究人员还对本科生和硕士生进行CT扫描数据处理、3D打印、计算机编码和基础化石制备等方面的培训。研究人员计划将该项目产生的所有数据，如CT扫描数据和数据矩阵，免费提供给公共在线存储库，以允许可重复性，并使未来的灵长类动物进化研究成为可能。蛇形颅骨传统上在灵长类起源的假设中扮演着重要的角色，但仍然知之甚少，因为它们对大多数蛇形物种来说是未知的，因为许多已知的颅骨标本没有使用现代CT技术进行分析。本研究使用现代高分辨率CT技术记录新的蛇颈适应性颅骨解剖，重新评估先前发表的颅骨描述，并在灵长类动物和其他胎盘哺乳动物之间进行彻底的颅骨比较。这些数据被合并到一个新的特征-分类群矩阵中，该矩阵使用简约和贝叶斯系统发育方法进行分析，以评估进化关系。这些分析的结果可以让研究人员评估(i)在蛇适应动物和现代灵长类动物之间，如果有的话，哪些颅骨特征是唯一共享的，（ii）蛇适应动物家族之间的相互关系，以及（iii）在原始动物中关于蛇适应动物进化关系的假设。最终，这些新数据可以澄清先前提出的蛇适应动物和现代灵长类动物之间共同的颅骨特征，并将有助于更好地理解灵长类动物与其他哺乳动物的差异以及灵长类动物进化史的第一步。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Central to unraveling the origin of primates - the mammalian group to which humans belong - are the fossils of plesiadapiforms, extinct members of a group (Euarchonta) consisting of primates and closely related mammals. While some plesiadapiforms have long been suggested to share characteristics with some contemporary primates, additional analyses of the plesiadapiforms using newer, state-of-the-art methodologies can further advance our understanding of primate origins. This doctoral dissertation project uses methods such as high-resolution X-ray micro computed tomography (μCT) to analyze and compare the cranial anatomy of plesiadapiforms to that of extant primates and other placental mammals. Detailed cranial comparisons are generated that can add to the evaluation of evolutionary relationships among plesiadapiforms, extant primates, and other euarchontan mammals, in the context of a new evolutionary tree. This project also provides numerous opportunities for outreach through mentorship, public science engagement events, and data sharing. Insights from this project can be incorporated into programs that facilitate participation from groups underrepresented in STEM. The investigators also train undergraduate and master’s students in aspects of CT scan data processing, 3D printing, computer coding, and basic fossil preparation. The investigators plan to make all data generated from this project, such as CT scan data and data matrices, freely available on public online repositories to allow for repeatability and to enable future studies on primate evolution.Plesiadapiform crania have traditionally played an important role in hypotheses about primate origins but remain poorly understood because they are unknown for a large majority of plesiadapiform species and because many of the known cranial specimens have not been analyzed using modern CT techniques. This study uses modern high-resolution CT technology to document new plesiadapiform cranial anatomy, reevaluate previously published cranial descriptions, and make thorough cranial comparisons among primates and other placental mammals. These data are incorporated into a new character-taxon matrix that is analyzed using both parsimony and Bayesian phylogenetic methods to assess evolutionary relationships. Results from these analyses can allow investigators to assess (i) which, if any, cranial features are uniquely shared among plesiadapiforms and primates of modern aspect, (ii) interrelationships among plesiadapiform families, and (iii) hypotheses of plesiadapiform evolutionary relationships within Euarchonta. Ultimately, these new data can provide clarity on previously proposed shared cranial features among plesiadapiforms and primates of modern aspect and will promote a better understanding of the divergence of primates from other mammals and the first steps in primate evolutionary history.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.