AILSA CHANG, HOST:
The birds of today descended from the dinosaurs of yore. But researchers have known relatively little about the bird's brain and how it took shape over millions of years. Science reporter Ari Daniel describes a new fossil that sheds light on that mystery.
ARI DANIEL, BYLINE: Bird brain should be a compliment. Daniel Field is a vertebrate biologist at the University of Cambridge.
DANIEL FIELD: Birds are one of the most intelligent groups of living vertebrate animals. They really rival mammals in terms of their relative brain size and the complexity of their behaviors.
DANIEL: But it's been hard to piece together how bird brains evolved. First, most of the fossil evidence dates back to tens of millions of years before the end of the Cretaceous, when dinosaurs went extinct and birds really diversified. And those fossils of feathered dinosaurs that have turned up often have a key problem, says paleontologist Luis Chiappe with the Natural History Museum of Los Angeles County.
LUIS CHIAPPE: They're beautiful, but they're all like roadkill. They're all flattened. And there are aspects that you're never going to be able to recover from those fossils.
DANIEL: Such as the shape and 3D structure of the brain. Then in 2016, a Brazilian paleontologist discovered a remarkably well-preserved fossil in Sao Paulo state. It came from a prehistoric bird that fills in a crucial gap. The animal in question lived 80 million years ago, so before the dinosaur mass extinction event.
CHIAPPE: Relatively small bird, something the size of between a pigeon and a starling. It would have been an active flyer, you know, fully feathered.
DANIEL: And its skull, he says...
CHIAPPE: It's very modern-looking, strikingly modern-looking.
DANIEL: The researchers were able to CT scan this intact, delicate skull, allowing them to digitally reconstruct the animal's brain. Some parts were more dinosaur-like, says Daniel Field.
FIELD: For instance, the portion of the brain that in modern birds is responsible for helping coordinate flight, called the cerebellum, is not very well-developed in this new fossil.
DANIEL: On the other hand, the cerebrum, the part of the brain associated with higher-level cognition, was pretty big, much larger than that of the bird-like dinosaurs that came before and almost as large as modern birds.
FIELD: It tells us these sorts of transitional birds, they may well have been very clever and indeed much more clever than anything that had previously come before.
DANIEL: Which would've likely helped these ancient birds find food or mates. And more complex cognition could've supported a more complex social structure. The research is published in the journal Nature.
For NPR News, I'm Ari Daniel.
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