EVOLUTION OF WHALE SENSORY SYSTEM MORPHOLOGY: CURRENT KNOWLEDGE AND FUTURE DIRECTIONS (Invited Presentation)

Studies surrounding the evolution of sensory system anatomy in cetaceans over the last ~100 years have shed light on aspects of the early evolution of hearing sensitivities, the small relative size of the organ of balance (semicircular canals and vestibule), brain (endocast) shape and relative volume changes, and ontogenetic development of sensory-related structures. In this talk I review advances in our knowledge of whale sensory system morphology as informed by the use of nondestructive imaging techniques, with a focus on applied methods in computed tomography (CT and μCT) and identify the key questions that remain to be addressed. These questions include: Is lower frequency hearing sensitivity the ancestral condition for whales, and, if so, at what point did the lineage acquire low frequency hearing sensitivities? Did echolocation evolve more than once in odontocetes; and if so, when and why? How has the structure of the cetacean brain changed throughout the evolution of whales, and do these modifications correspond to transitions in hearing sensitivities? Finally, what are the general pathways of ontogenetic development of sensory systems in odontocetes and mysticetes? Answering these questions will allow us to understand important macroevolutionary patterns in a fully aquatic mammalian group, and provide baseline data on species for which we have limited biological information because of logistical limitations.