DISSERTATION RESEARCH: The Evolution of Crocodylian Cranial Development

鳄鱼（鳄鱼和短吻鳄）通常被称为“活化石”，通常被认为具有古老而保守的骨骼解剖结构和生活方式。然而，现代鳄鱼的种类比人们通常认为的要多，尤其是它们的头骨，从短而宽到长而细长。先前的研究表明，鳄鱼的头骨形状与饮食和栖息地的特殊化有关，但这些形状是如何形成的尚不清楚。鳄鱼颅骨多样性的形成与发育有关：个体从受精卵成长为成年人的过程中发生的变化。发育过程是由基因控制的，基因表达方式的改变可以改变发育途径和成人解剖结构。通过结合化石、鳄鱼胚胎和现代发育生物学技术的数据，该项目将揭示哪些发育途径的变化是鳄鱼头骨进化的关键，以及鳄鱼的进化多样性。从这项研究中获得的见解也可能告诉我们脊椎动物基因组、发育和有机体复杂性之间的一般联系。为了充分利用公众对鳄鱼及其近亲（恐龙和鸟类）的兴趣，该项目将与哈佛自然历史博物馆（HMNH）合作，为学生和教师开发K-12活动。这些活动探索古生物学和发育生物学的关键概念，并将与下一代科学标准联系起来。HMNH提供了一个独特的场所，可以吸引来自波士顿大都会地区的不同城市观众和来自世界各地的游客。独特的形态特征区分了鳄鱼、哺乳动物和鸟类等主要动物群体。这些特征对这些群体的特定生活方式和习惯非常重要，对他们数百万年来的生存至关重要。这种多样性的形成是由新基因的进化、基因的新功能或基因表达发育模式的改变引起的。结合化石、胚胎和发育遗传技术，本研究将揭示鳄鱼颅骨多样性进化的发育机制。本项目将利用原位杂交技术研究与现存鳄鱼颅骨发育有关的关键基因的表达模式。将分析八个目标物种的发育阶段，这些物种广泛地代表了现代鳄鱼的系统发育和鼻子形状的多样性。该项目旨在通过实验复制祖先和衍生的基因表达模式，并使用几何形态计量学来量化表达模式与头骨形状之间的关系。这些短吻鳄胚胎的功能研究将检验发育中的特定变化是否可能是解剖学进化变化的原因。该项目整合了古生物学、解剖学和发育生物学，通过发育将解剖学的变化与基因遗传联系起来。这种综合的方法将导致对解剖多样性和生物新特征进化的关键机制的更好理解。

Crocodylians (crocodiles and alligators), often labeled 'living fossils, are commonly thought to have an ancient and conservative skeletal anatomy and lifestyle. However, modern crocodylians are more diverse than often appreciated and their skulls, in particular, can range from short and wide to incredibly long and slender. Prior research has shown that crocodylian skull shape is correlated with dietary and habitat specializations, but it remains unclear how these shapes come to be. The formation of crocodylian skull diversity is tied to development: the changes that occur in an individual as it grows from a fertilized egg to an adult. The process of development is controlled by genes, and changes to how genes are expressed can modify developmental pathways and adult anatomy. By combining data from fossils, crocodylian embryos, and modern developmental biology techniques, this project will reveal which changes in developmental pathways were key to the evolution of the crocodylian skull, and the evolutionary diversity of crocodylians. Insights from this research may also inform general connections between genomic, developmental and organismal complexity in vertebrates. To capitalize on the public interest in crocodiles and their relatives (dinosaurs and birds), this project will develop K-12 activities for students and teachers in conjunction with the Harvard Museum of Natural History (HMNH). These activities explore key concepts in paleontology and developmental biology and will be tied to the Next Generation Science Standards. The HMNH provides a unique venue to reach a diverse urban audience from across the Boston Metropolitan area and visitors from around the world. Unique morphological features distinguish major groups of animals like crocodylians, mammals, and birds. These features are important for the particular lifestyles and habits of these groups and have been critical for their survival over millions of years. The formation of this diversity is caused by the evolution of novel genes, novel functions for genes, or modification to the developmental pattern of gene expression. Integrating fossils, embryos, and developmental genetic techniques, this study will reveal developmental mechanisms involved in the evolution of crocodylian cranial diversity. This project will study the expression patterns of key genes involved in the development of the skull in extant crocodylians using in situ hybridization. Developmental stages from eight target species, which broadly sample the phylogeny and diversity of snout shapes in modern crocodylians, will be analyzed. The project aims to experimentally replicate ancestral and derived gene expression patterns and to use geometric morphometrics to quantify the relationship between expression patterns and skull shapes. These functional studies in alligator embryos will test the likelihood that particular changes in development were the cause of evolutionary changes in anatomy. This project integrates paleontology, anatomy, and developmental biology to link changes in anatomy to genetic inheritance through development. This integrative methodology will lead to a greater understanding of critical mechanisms underlying the evolution of anatomical diversity and novel features of organisms.