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

Harvard University, Cambridge MA

Investigators

Abstract

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.