Unique Brain Structures Might've Helped Ancient Birds Outlive Nonavian Dinosaurs

An examination of a recently-excavated bird fossil suggests that their unique brain shape might have helped these ancient birds survive the Chicxulub asteroid impact - an extinction event that wiped out nonavian dinosaurs 66 million years ago.

Led by the University of Texas at Austin, the new study revolves around the physiological clues from the fossil - dated to be 70 million years old and still has its skull almost intact - considered a rare case in the fossil record that allowed unprecedented discovery and comparison with its extant relatives.

Researchers present their findings in the open-access article, "Bird neurocranial and body mass evolution across the end-Cretaceous mass extinction: The avian brain shape left other dinosaurs behind," appearing in the recent Science Advances journal.

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Saved by Unique and Complex "Bird Brains"

"Living birds have brains more complex than any known animals except mammals," said Christopher Torres, lead investigator of the new study while he was still a Ph.D. student from the College of Natural Sciences at UT, in an article from Forbes. Torres is now serving as a National Science Foundation (NSF) postdoctoral fellow at Ohio University and a research associate at the University of Texas Jackson School of Geosciences. He adds that the new fossil allowed them to test the notion that these ancient birds survived because of their unique brain.

The fossil is a new specimen for a bird known as Ichthyornis, a now-extinct seabird that expired simultaneously as other nonavian dinosaurs or dinosaurs that are not birds. This specimen lived in Kansas during the late Cretaceous, which, according to the National History Museum, is a period defined as being 100.5 million years ago to 66 million years ago, marked by the Chicxulub asteroid event. In the study, the Ichthyornis is described as having both avian and nonavian dinosaur-like traits such as a jaw full of teeth but ends in a beak. Its intact skull allowed the researchers to better examine the unique structure.

The Secret of Avian Skulls

In birds, their skulls are wrapped more tightly around their brains. Researchers verified it by using scans to recreate the 70 million-year-old specimen in a 3D replica. They then compared this structure with brains and skulls from extant birds.

They found that the Ichthyornis brain was more common with nonavian dinosaurs than the birds we have today. Specifically, researchers noted how the cerebral hemispheres in the extinct seabird - the parts that handle higher cognitive functions like speech and emotion in humans - are significantly larger in extant birds than their extinct ancestors. Their findings suggest that having a bigger brain and the higher cognitive functions that come with it might have something to do with their survival.

Birds generally have large brains compared to the size of their heads. Additionally, they have been observed to have a range of intelligent behaviors - memory, problem-solving, with others suggesting that birds have a sense of self-consciousness. Finding and studying skulls from these ancient birds and related dinosaurs have remained a challenge for paleontologists, especially since their bones are more brittle and rarely remain intact in three dimensions.