Collaborative Research: The Origin of the Large Brains of Cetaceans

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Cetaceans (whales, dolphins, porpoises) have the largest brains on the planet, ever. Even when scaled for body size, cetacean brains are second only to humans in size. Expansion of brain size in cetaceans has been considered a consequence of echolocation and/or an increase in the number of neurons. This project will use the study of fossil cetaceans to identify factors lead to brain expansion. Because cetaceans are a charismatic group of mammals with an exceptional fossil record, this study will use brain evolution as a case study that engages high school juniors and seniors from a rural STEM school in Ohio, as well as Alaskan high school and college students. Students will take a course focused on Whales, Seals, and Evolution, which integrates broader geological and biological concepts. A symposium organized by the Sitka Science Center in Alaska will be used to present findings to the general public. This study analyzes a collection of the earliest fossil cetaceans to identify factors contributing to the evolution of brain size. The project team will test the hypothesis that the acquisition of echolocation led to increases in brain size. This will be accomplished by studying changes in ear shape in fossil whales over time to identify when high-frequency hearing evolved. In addition, the team will test whether size increases in the cetacean brain are a consequence of increasing numbers of neurons or other support cells. This will be accomplished by comparing the number of neurons within the brains of living echolocating and non-echolocating whales relative to other cells within the brain. This study will further understanding of cetacean evolution by pinpointing when the expansion of the brain occurred, how this expansion relates to the onset of high-frequency hearing, and by quantifying the diversity and abundance of cells within the brain.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.