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，特别是喙或喙的进化所驱动的。一个关键的进化创新，如鸟喙，只能通过研究其最终和近似原因来充分解释——导致喙结构外观的大规模进化模式和必须改变的发育过程，分别将爬行动物的脸变成鸟喙。本研究将通过对化石记录的定量分析，追踪鸟类进化过程中从非鸟类爬行动物面部到独特鸟类喙的转变过程，追踪鸟类进化过程中转变的顺序和性质。利用这些信息，研究人员将用鸡和鳄鱼（鸟类的近亲）和蜥蜴的胚胎作为比较材料，解剖每一种转化背后的近似分子发育机制。通过在鸡胚胎中复制“爬行动物”状态，产生类似祖先条件的改变表型，将为基因表达变化的重要性假设提供实验支持。这项对鸟类面部进化的详细、综合的研究，将有助于深入了解导致今天地球上主要辐射的关键进化转变的基本性质和机制。理解这些转变是理解生物多样性和生物差异背后驱动力的核心。很少有研究能如此全面地考察一个主要适应特征的生物学。此外，这项工作将广泛整合，因为先进的分子发展调查将与遗产博物馆和数字收藏活动紧密联系在一起。甚至在发育工作中使用的胚胎也将在哈佛博物馆中找到一个永久的档案馆。这种与博物馆的紧密联系使其易于与公众沟通。以这项工作为基础的展览将吸引公众使用具有魅力的研究对象——鸟类、恐龙和鳄鱼——并将代表将这些经典的自然历史主题与前沿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.