Researchers trace the history of brain evolution from tyrannosaurs to modern crows

An international team of evolutionary biologists and paleontologists has reconstructed the evolution of the avian brain using a massive dataset of brain volumes from dinosaurs, extinct birds such as Archeopterix and the Great Auk, and modern birds.

The study, published online today in the journal. Current biology, reveals that before the mass extinction at the end of the Cretaceous period, birds and non-avian dinosaurs had similar relative brain sizes. After the extinction, the brain-body scaling ratio changed dramatically as some types of birds underwent explosive radiation to reoccupy the ecological space unoccupied by extinct groups.

“One of the big surprises was that selection for a small body size turns out to be an important factor in the evolution of big-brained birds,” says Dr. Daniel Ksepka, Science Curator at the Bruce Museum and lead author of the study. . “Many successful bird families developed proportionally large brains by reducing to smaller body sizes, while their brain sizes remained close to those of their larger-bodied ancestors.”

To understand how birds’ brains changed, a team of 37 scientists used computed tomography data to create endocasts (models of the brain based on the shape of the skull cavity) of hundreds of birds and dinosaurs, which they combined with a Large existing database of brain measurements from modern birds. They then looked at brain-body allometry – how the size of the brain scales with the size of the body.

Relative brain size in> 2000 species of birds and dinosaurs. Warmer colors indicate proportionally larger brain sizes. Credit: Bruce Museum

“There is no clear line between the brains of advanced dinosaurs and primitive birds,” says co-author Dr. Amy Balanoff of Johns Hopkins University. “Birds like emu and pigeons have the same brain size that you would expect for a theropod dinosaur of the same body size, and in fact, some species like moa have smaller brains than expected.”

The two groups of birds with truly exceptional brain sizes evolved relatively recently: parrots and corvids (crows, crows, and relatives). These birds display tremendous cognitive ability, 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 proportional brain sizes.

“Several groups of birds show above-average rates of brain and body size evolution,” says co-author Dr. N. Adam Smith of the Campbell Museum of Geology at Clemson University. “But crows are really out of line: They outperformed all other birds. Our results suggest that calling someone a ‘bird brain’ is really a great compliment.”

“Ravens are hominins in the bird kingdom,” says co-author Dr. Jeroen Smaers of Stony Brook University. “Like our own ancestors, they developed proportionally massive brains by increasing both the size of their body and that of their brain at the same time, and the increase in brain size occurred even more rapidly.”

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