Evolution, Development, and Morphology of Cetacean Skull Novelties

Novelty presents a paradox in evolutionary biology. Novel features appear to be qualitatively unique to a specific type of organism, but historical continuity requires that some common form must have pre-existed them. This dissertation focuses on the morphology and development of three inter-related evolutionary novelties of cetacean skulls: telescoping, the blowhole, and extensive maxillo-frontal overlap. To investigate these novelties, museum specimens and skulls collected from stranded dolphins were studied using computed tomography, morphometrics, and histological methods. The first part of this dissertation sets an evolutionary-developmental framework for empirical study of skull telescoping, defined as extensive bone overlap and shortened maxillo-occipital distance (Chapter 2). The following two chapters (3 and 4) identify distinct ontogenetic changes that contribute to reorientation of the blowhole in a dolphin species and the fin whale. Lastly, the maxillo-frontal in the bottlenose dolphin was characterized using computed tomography and histological methods (Chapter 5).