Marine mammal sensory system evolution

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Neuroanatomy

How did marine mammal brains evolve and adapt to an aquatic lifestyle? Primarily I aim to answer this question using digital endocasts, as they are our only window into the brain and endocranial shape of extinct (fossil) species, which provide a deep time perspective, or rare species for which sometimes our only data are osteological material. The whale brain is of particular interest because one modern lineage (toothed whales, Odontoceti) evolved echolocation, while another (baleen whales, Mysticeti) evolved a unique mode of feeding for a mammal (filter feeding), using a novel anatomical structure known as baleen, which replaced their teeth. Both lineages are highly social, some having tool use, and can become large in size because there are fewer size limitations in an aquatic environment, and so brain-to-body size ratios may not be good predictors of intelligence. Current projects include pinniped (seal and sea lion) brain evolution and neuroanatomy of an archaic baleen whale. I received pilot funding for a comprehensive (including at least one member of all genera) whale brain evolution study (Paleontological Society A.J. Boucot Grant), and am seeking larger-scale grant funding for this work. 

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inner ears

What are the hearing ranges of modern and extinct marine mammals? How have they evolved? Hearing is one of the most important sensory modalities underwater. My research has centered on estimating hearing sensitivity in marine mammals using morphology and comparisons with audiogram measurements and recordings from the wild. One of my current projects is a comprehensive study of morphologically-inferred hearing sensitivity in beaked whales (Ziphiidae), a mysterious group of large echolocating toothed whales that are mostly pelagic deep divers (funded in part by two John E. Heyning awards). Other projects include examination of the inner ear morphology of melon-headed dolphins (Globicephalinae), extinct river dolphins (genus Parapontoporia), and archaic Oligocene dolphins. Ultimately a phylogenetically-informed synthesis pulling together full taxonomic coverage of extant and fossil cetaceans will be performed.

Ontogenetic Sequence Analysis (top image) constructed with assistance from Dr. Matthew Colbert. Red line indicates modal distribution. Bottom image represents some  Phocoena phoceona  fetal specimens used in the analysis from the Copenhagen Museum of Natural History.

Ontogenetic Sequence Analysis (top image) constructed with assistance from Dr. Matthew Colbert. Red line indicates modal distribution. Bottom image represents some Phocoena phoceona fetal specimens used in the analysis from the Copenhagen Museum of Natural History.

Evolution of Development

Does development inform on the evolution of novel sensory or feeding structures such as the biosonar apparatus in toothed whales, or baleen in baleen whales? Although we can't perform actual evo-devo experiments on marine mammals because of their protected status, we can peek into their developmental story using staining techniques to enhance contrast in CT scans of wet museum specimens to better visualize the development of tissues. I am currently seeking funding to acquire the data to test hypotheses on the development and evolution of unique aquatic sensory adaptations, like the biosonar apparatus in toothed whales, and including changes in the brain and inner ears in cetaceans and pinnipeds.