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Study of Bird and Dinosaur Brains Illuminates Evolution

Bird brains
Jeroen B. Smaers
Jeroen B. Smaers

Stony Brook’s Jeroen Smaers is senior author of a paper setting forth the findings of an international team of evolutionary biologists and paleontologists that reconstructed the evolution of the avian brain using a massive dataset of brain volumes from dinosaurs, extinct birds like Archaeopteryx and the Great Auk, and modern birds.

The study, published online in the journal Current Biology, reveals that prior to the mass extinction at the end of the Cretaceous Period, birds and non-avian dinosaurs had similar relative brain sizes. After the extinction, things changed dramatically and the brain-body scaling relationship rapidly shifted as some types of birds underwent an explosive radiation to re-occupy ecological space vacated by extinct groups.

In order to understand how bird brains changed, a team of 37 scientists used CT scan data to create endocasts (models of the brain based on the shape of the skull cavity) of hundreds of birds and dinosaurs, which they then combined with a large existing database of brain measurements from modern birds. They then analyzed brain-body allometry: the way brain size scales with body size.

Bird brains
Visualizations of brain endocasts (blue) from the skulls of a dinosaur and a modern bird. Image courtesy of Witmer Lab at Ohio University.

The geniuses of the bird world are two groups that evolved relatively recently: parrots and corvids (crows, ravens, and kin). These birds show tremendous cognitive capacity, including the ability to use tools and language, and remember human faces. The new study finds that parrots and crows exhibited very high rates of brain evolution that may have helped them achieve such high proportional brain sizes.

“Crows are the hominins of the bird kingdom,” said co-author Dr. Smaers, associate professor in the Department of Anthropology. “Like our own ancestors, they evolved proportionally massive brains by increasing both their body size and brain size at the same time, with the brain size increase happening even more rapidly.”

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