DISSERTATION RESEARCH: The Evolution of Mammalian Dentition: Insights from fossil synapsid histology

哺乳动物的起源一直是科学家们感兴趣的问题，因为哺乳动物是地球上最多样化的动物群体之一。这项研究调查了现代哺乳动物（兽脚类）祖先的某些复杂牙齿特征是如何进化的，从而使我们了解了驱使哺乳动物从“爬行类”祖先进化的选择力量。哺乳动物的牙齿被认为比爬行动物更复杂、更特化；然而，这些假设并没有完全考虑到灭绝的物种。因此，复杂牙齿特征的进化并没有完全被理解，这使得我们对古代哺乳动物的生态学和进化的理解不完整。这项工作的组织学数据和分析将提供给科学界，这些数据将对对脊椎动物进化感兴趣的系统学家有用。通过自然历史博物馆的展览和项目向公众宣传也将进行。哺乳动物的齿列在现存脊椎动物中是独一无二的，兽头类化石揭示了哺乳动物创新的进化，如区域化齿列（异齿）、多牙根和牙齿对牙齿咬合。虽然使用大体形态来评估这些特征相对简单，但其他重要特征的演变只能通过组织学薄片来检查，因此许多化石分类群仍然未知。本研究通过使用古组织学和微计算机形态数据来确定兽脚类重要牙齿特征的特征状态，填补了这一空白。初步数据表明，曾经被认为是哺乳动物独有的牙齿特征在兽头类动物的祖先身上进化了多次。该项目还测试了牙齿和哺乳动物以及独立进化出这些复杂特征的爬行动物类群的生活史特征之间的相关进化。这项工作将为哺乳动物创新获得的选择压力提供洞见。

The origin of mammals has long been of interest to scientists because mammals are one of the most diverse groups of animals on the planet. This research investigates how certain complex dental characteristics evolved in the ancestors of modern mammals (therapsids), and thus informs our understanding of the selective forces driving mammalian evolution from their "reptile-like" ancestors. Mammal teeth are considered more complex and specialized than reptiles; however, these assumptions have not fully considered extinct species. As such, the evolution of complex dental traits is not entirely understood, which leaves our understanding of the ecology and evolution of ancient mammals incomplete. Histological data and analyses from this work will be made available to the scientific community, and the data will be useful for systematists interested in the evolution of vertebrates. Public outreach through displays and programs at natural history museums will also occur. The dentition of mammals is unique among living vertebrates, and therapsid fossils have shed light on the evolution of mammalian innovations like a regionalized dentition (heterodonty), multiple tooth roots, and tooth-to-tooth occlusion. While it is relatively straightforward to assess these characters using gross morphology, the evolution of other significant features can only be examined through histological thin sections, and thus remain unknown for many fossil taxa. This research fills this void by using paleohistology and micro-computed tomorgraphy data to determine character states for important dental traits in therapsids. Preliminary data suggest that dental traits once thought exclusive to mammals evolved multiple times in their therapsid forebears. This project also tests for correlative evolution between dental and life history traits along the mammal line as well as in reptilian taxa that have independently evolved these complex traits. The work will provide insight into the selective pressures on the acquisition of mammal innovations.