Today, being “foolish” means forgetting where you left your keys or wallet. But 66 million years ago, that may have made the difference between life and death – and may help explain why birds are the only dinosaurs left on Earth.
Research on a newly discovered bird fossil conducted by the University of Texas at Austin revealed that a unique brain shape could be the reason that the ancestors of living birds survived the mass extinction that cost life to all other known dinosaurs.
“Living birds have more complex brains than any known animal except mammals,” said lead researcher Christopher Torres, who conducted the research while earning a doctorate. from UT’s College of Natural Sciences and is now a Postdoctoral Fellow at the National Science Foundation at Ohio University and a Research Associate at UT Jackson School of Geosciences. “This new fossil finally allows us to test the idea that these brains played a major role in their survival.”
The fossil is around 70 million years old and has an almost complete skull, a rare event in the fossil record that has allowed scientists to compare the ancient bird to birds living today.
The results were published on July 30, 2021 in the journal Scientists progress.
The fossil is a new specimen of a bird named Ichthyornis, who went extinct along with other non-avian dinosaurs and lived in what is now Kansas by the end of Cretaceous Period. Ichthyornis has a mix of avian and non-avian dinosaur characteristics – including toothy jaws but with a beak. The intact skull allowed Torres and his collaborators to take a closer look at the brain.
Bird skulls wrap tightly around their brains. With CT imaging data, the researchers used the skull of Ichthyornis like a mold to create a 3D replica of his brain called an endocast. They compared this endocast with those created for living birds and more distant dinosaur relatives.
The researchers found that the brain of Ichthyornis had more in common with non-avian dinosaurs than living birds. In particular, the cerebral hemispheres – where higher cognitive functions such as speech, thought, and emotions occur in humans – are much larger in living birds than in birds. Ichthyornis. This diagram suggests that these functions could be linked to survival to mass extinction.
“If a feature of the brain affected survival, we would expect it to be present in survivors but absent in victims, such as Ichthyornis, Torres said. “This is exactly what we see here.”
The search for the skulls of primitive birds and closely related dinosaurs has been a challenge for paleontologists for centuries. Bird skeletons are notoriously fragile and rarely survive intact in the three-dimensional fossil record. Well-preserved skulls are particularly rare, but that’s exactly what scientists need to understand what their brains looked like in life.
“Ichthyornis is the key to unraveling this mystery, ”said Julia Clarke, professor at UT Jackson School of Geosciences and co-author of the study. “This fossil helps us get much closer to answering some lingering questions about living birds and their survival among dinosaurs.”
Reference: “Bird neurocranial and body mass evolution across the end-Cretaceous mass extinction: The avian brain shape left other dinosaurs behind” by Christopher R. Torres, Mark A. Norell and Julia A. Clarke, July 30, 2021, Scientists progress.
DOI: 10.1126 / sciadv.abg7099
Mark Norell, curator and division director of paleontology at the American Museum of Natural History, is a co-author of the study. This work was funded by the Howard Hughes Medical Institute Science Education Program, the Jackson School of Geosciences, and the American Museum of Natural History.