Dissertation Research: The Deep Evolution and Development of the Archosaurian Head and the Origin of the Face of Birds

鸟类是现代陆地脊椎动物中最成功的一类。它们巨大的生态多样性很大程度上是由独特的鸟脸的进化推动的，特别是喙或喙。一项关键的进化创新，如鸟喙，只能通过研究其最终原因和近期原因才能得到充分解释--分别是导致喙结构出现的广泛进化模式和将爬行动物的脸变成鸟喙必须改变的发育过程。这项研究将通过将定量技术应用于化石记录，追踪鸟类进化过程中的变化序列和性质，来追踪从非鸟类爬行动物的脸到独特的鸟类喙的转变。利用这些信息，将使用鸡以及鳄鱼(与鸟类最接近的现存亲属)和蜥蜴的胚胎作为比较材料，剖析每一次转变背后的最接近的分子发育机制。通过在鸡胚胎中复制“爬行动物”状态，产生一种类似于祖先状态的改变表型，将为基因表达变化的重要性假说提供实验支持。这项对鸟脸进化的详细、综合研究将提供对导致当今地球上主要辐射的关键进化转变的基本性质和机制的洞察。理解这些变化是理解生物多样性和生物差异背后驱动力的核心。很少有研究如此全面地研究一个主要适应特征的生物学问题。此外，这项工作将是广泛整合的，因为先进的分子发展调查将在很大程度上与遗产博物馆和基于数字收藏的活动联系在一起。即使是在研发工作中使用的胚胎也会在哈佛博物馆的收藏品中找到永久档案。与博物馆的这种密切联系很容易为公众沟通。基于这项工作的展览将利用富有魅力的研究对象-鸟类、恐龙和鳄鱼-吸引公众，并将代表着将这些经典自然历史主题与尖端分子科学联系起来的绝佳机会。

Birds represent the most successful group of modern land vertebrates. Much of their enormous ecological diversity is driven by evolution of the unique bird face, specifically the beak or bill. A key evolutionary innovation, such as a bird beak, can only be fully explained by examining both its ultimate and proximate causes -- the broad-scale evolutionary patterns of change leading to appearance of beak structure and the developmental processes that must be altered to turn a reptilian face into a bird beak, respectively. This study will trace the transition from a nonavian reptile face to the unique bill of birds by applying quantitative techniques to the fossil record, tracing the sequence and nature of transformations during bird evolution. Using that information, the proximate molecular developmental mechanisms behind each transformation will be dissected using chickens and, as comparative material, embryos of crocodylians (the closest living relatives to birds) and lizards. Experimental support for hypotheses about the significance of changes in gene expression will be provided by replicating 'reptilian' states in chicken embryos, producing an altered phenotype that resembles the ancestral condition. This detailed, integrative study of the evolution of the bird face will provide insight into the fundamental nature and mechanisms of key evolutionary transitions that lead to the major radiations populating the earth today. Understanding these transformations is at the core of comprehending the driving forces behind biodiversity and biological disparity. Few studies have so comprehensively examined the biology of a major adaptive feature. Moreover, this work will be broadly integrative in that the advanced molecular development investigations will be tied heavily to legacy museum and digital collection based activities. Even embryos used in the developmental work will find a permanent archive in the Harvard museum collections. This close tie to the museum lends itself easily to public communication. Exhibits based on this work will draw in the public using the charismatic study subjects -- birds, dinosaurs, and crocodiles -- and will represent a prime opportunity to tie such classical natural history subjects to cutting-edge molecular science.