(CNN)Being called a "bird brain" may be closer to a compliment than an insult.
That's because new research suggests that some birds evolved over time to have smaller bodies and maintain large brains.
Researchers studied the endocasts of skulls belonging to hundreds of dinosaurs and extinct birds.
They used CT scans of the animals' ancient skulls to create endocasts, which act like an imprint of the brain in the skull, reflecting brain sizes (since brains don't fossilize). Then, they compared the brain sizes with brain measurements of modern birds in a large data set.
The brain measurements were analyzed along with body size to compare the scale of brain size to body size.
Together, the evolutionary biologists and paleontologists were able to show the timeline for bird brain evolution. The study published Thursday in the journal Current Biology.
Before the mass extinction event that killed off the dinosaurs 66 million years ago, the researchers discovered that birds and large dinosaurs had brains that were very similar in size.
But some birds went through what the researchers refer to as a "scaling" event after the dinosaurs went extinct.