Out of the skulls of babes. Modern birds have skulls that look remarkably like those of juvenile dinosaurs, offering an unusual explanation for how birds came to have relatively large brains.
As dinosaurs evolved into birds, something arrested their development. The juvenile heads they kept may be responsible for their relatively high intelligence, and their incredible evolutionary success.
Bhart-Anjan Bhullar of Harvard University and colleagues took photos and CT scans of skulls belonging to juvenile and adult dinosaurs, extinct and modern birds, and more distant relatives like crocodiles.
They found that compared to their ancestors, birds’ faces became flattened, and their brain cases relatively larger. That’s exactly what young dinosaurs’ skulls looked like.
“This could be a landmark study,” says Gregory Erickson of the Florida State University in Tallahassee. “When you look at a bird you’re looking at a young dinosaur.”
Like bird like human
This switch to a more juvenile skull shape was also an important force in human evolution. Adult human skulls look much like those of baby chimpanzees, with flattened faces and over-sized brain cases.
In fact, major evolutionary changes often rely on changes to development, because it’s relatively easy to change the pace of an animal’s development, producing adults that may look very different to their ancestors.
For birds, switching to a more baby-like skull shape eventually unleashed their potential. In particular, having larger skulls relative to their body size allowed birds to evolve relatively large and more elaborate brains.
Bhullar’s group is trying to reverse bird evolution, tweaking the genes of chickens to make them revert to their dinosaur ancestors. Last year, his supervisor Arkhat Abzhanov persuaded a chicken embryo to grow a snout rather than a beak. Bhullar says he hasn’t yet found the genes underpinning the changes in birds’ skulls, but if he does, he could give a chicken the head of a dinosaur.
Journal reference: Nature, DOI: 10.1038/nature11146
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