Temporal Patterns in Tooth Morphology in Secondarily Aquatic Tetrapods

We investigated how dental morphology has changed over time in secondarily aquatic tetrapods: vertebrate clades with terrestrial ancestors who evolved into fully aquatic or marine forms. Such clades include crocodilians, ichthyosaurs, mosasaurs, and cetaceans. Secondarily aquatic tetrapods are characterized by a myriad of morphological changes such as limb reduction, body streamlining, and sensory organ alteration. The teeth and skulls of extant and fossil cetaceans and crocodilians were examined using museum specimens and image repositories. We used ImageJ to measure the dimensions of the skulls and teeth. The results suggest that dental morphology was influenced by the body size and feeding method (observed or inferred) of each species. Crocodilian tooth shape was more affected by body size than by temporal patterns. Cetacean dental morphology diverged over time into two lineages, each characterized by the retention of teeth or replacement of teeth by baleen. Within the extant toothed whales, dental morphology exhibits variation in size but convergence of shape. The results of this investigation will shed light on patterns of convergent evolution in the secondarily aquatic vertebrates