Dinosaurs evolved into modern birds in the late Jurassic Period. Exactly how this happened has been recorded in the skulls of dinosaurs, ancient birds and several transitional species.

It's long been known that birds and dinosaurs were very closely related. But a lot of the questions about how they were related, and how they evolved from one to the other, are still being answered today.

The roof of the skull in particular went through a period of dramatic change during the evolution from dinosaurs to birds. Scientists have traced exactly how this happened in a study in the journal Nature Ecology and Evolution.

"Across the dinosaur-bird transition, the skull transforms enormously and the brain enlarges," said study author Bhart-Anjan Singh Bhullar of Yale University.

"We were surprised that no one had directly addressed the idea that the underlying parts of the brain – the forebrain and midbrain – are correlated or somehow developmentally related to the overlying frontal and parietal bones."

The changes in the skull were closely mapped, with profound changes to the animals' brains. Specific regions of the brain transformed more than others, shaped by the new challenges the creatures faced in the transition from one evolutionary niche to another.

"We found a clear relationship between the frontal bones and forebrain and the parietal bones and midbrain," Bhullar said.

The researchers propose that this relationship between bone and brain regions holds beyond dinosaurs and birds. They suggest that in all species, skull shape could influence the size and shape of the brains they encase.

"What this implies is that the brain produces molecular signals that instruct the skeleton to form around it, although we understand relatively little about the precise nature of that patterning," Bhullar said.

"Ultimately, one of the important messages here is that evolution is simpler and more elegant than it seems. Multiple seemingly disparate changes – for instance to the brain and skull – could actually have one underlying cause and represent only a single, manifold transformation."

How dinosaur skulls morphed into bird skulls. Yale University