DISSERTATION RESEARCH: Independent evolution and ancestral conditions in the gnathostome axial column

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The presence of a backbone, even if only made of cartilage, is the feature that distinguishes vertebrate animals from their invertebrate relatives. Despite its central position in the body plans of all jawed vertebrates, the early evolutionary history and developmental mechanisms that gave rise to the vertebral column are not well understood. Across different vertebrate groups, and among fishes in particular, the vertebrae that make up the backbone are remarkably varied in their shape, composition, and structure. Furthermore, the early fossil record of the major groups of fishes shows that many evolved fundamental components of the vertebral column quite independently of others. The goals of this project are to document vertebral development in poorly studied groups such as sharks and skates, to determine how much independent evolution actually occurred in the deep history of vertebrae, and to provide essential comparisons with the current understanding of vertebral development in bony fishes.This project combines ancestral state reconstructions on gnathostome supertrees with computed tomography, gene expression, and fate mapping experiments to investigate the macroevolutionary patterns of vertebral evolution and development in fishes. Chondrichthyans are the main focus of the proposed research because they occupy a key phylogenetic position as the most proximate outgroup to the Osteichthyes. Chondrichthyans are often considered exemplars of ancestral vertebrate conditions in developmental and functional studies, but the primitive or derived status of much of their morphology is unclear and the subject of renewed research interest. Identifying ancestral conditions and homoplasy in the axial column complex is essential for the informed evaluation of studies and data obtained from alternative vertebrate model systems. Moreover, sharks as well as fossils are charismatic study subjects that effectively capture public interest. To help communicate the nature of this and other related projects to the public, the investigators will use computed tomographic scans (static and animated), and fossil shark specimens to educate students at local schools about the importance and relevance of evolutionary biology.