Paleontologists have unearthed the exquisitely preserved remains of Cretaceous enantiornithine bird in São Paulo state, southeastern Brazil. The extraordinary three-dimensional preservation of its skull allowed the researchers to digitally reconstruct the bird’s brain.
An artist’s impression of Navaornis hestiae. Image credit: Júlia D’Oliveira.
The newly-identified enantiornithine species lived in what is now Brazil, approximately 80 million years ago (Late Cretaceous epoch).
Scientifically named Navaornis hestiae, the ancient bird was roughly the size of a starling.
The species had a larger cerebrum than Archaeopteryx, suggesting it had more advanced cognitive capabilities than the earliest bird-like dinosaurs.
However, most areas of its brain, like the cerebellum, were less developed, suggesting that it hadn’t yet evolved the complex flight control mechanisms of modern birds.
“The brain structure of Navaornis hestiae is almost exactly intermediate between Archaeopteryx and modern birds — it was one of these moments in which the missing piece fits absolutely perfectly,” said Dr. Guillermo Navalón, a researcher at the University of Cambridge.
The fossilized remains of Navaornis hestiae were recovered in 2016 from William’s Quarry at the locality of Presidente Prudente, part of the Adamantina Formation in Brazil.
Tens of millions of years ago, the site was likely a dry area with slow-flowing creeks, which enabled the fossil’s exquisite preservation.
The extraordinary three-dimensional preservation allowed the paleontologists to use advanced micro-CT scanning technology to reconstruct the bird’s toothless and large-eyed skull and brain in remarkable detail.
The fossilized skeleton of Navaornis hestiae. Image credit: Stephanie Abramowicz.
“This fossil is truly so one-of-a-kind that I was awestruck from the moment I first saw it to the moment I finished assembling all the skull bones and the brain, which lets us fully appreciate the anatomy of this early bird,” Dr. Navalón said.
“Modern birds have some of the most advanced cognitive capabilities in the animal kingdom, comparable only with mammals,” added University of Cambridge’s Professor Daniel Field.
“But scientists have struggled to understand how and when the unique brains and remarkable intelligence of birds evolved — the field has been awaiting the discovery of a fossil exactly like this one.”
While the skull of Navaornis hestiae somewhat resembles that of a small pigeon at first glance, closer inspection reveals that it is not a modern bird at all but instead a member of, or the ‘opposite birds.’
Enantiornithine birds diverged from modern birds more than 130 million years ago, but had complex feathers and were likely competent flyers like modern birds.
However, the brain anatomy of Navaornis hestiae poses a new question: how did enantiornithines control their flight without the full suite of brain features observed in living birds, including an expanded cerebellum, which is a living bird’s spatial control center?
“This fossil represents a species at the midpoint along the evolutionary journey of bird cognition,” Professor Field said.
“Its cognitive abilities may have given Navaornis hestiae an advantage when it came to finding food or shelter, and it may have been capable of elaborate mating displays or other complex social behavior.”
“This discovery shows that some of the birds flying over the heads of dinosaurs already had a fully modern skull geometry more than 80 million years ago,” said Dr. Luis Chiappe, a researcher at the Natural History Museum of Los Angeles County.
The discovery is reported in a paper in the journal Nature.
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L.M. Chiappe et al. 2024. Cretaceous bird from Brazil informs the evolution of the avian skull and brain. Nature 635, 376-381; doi: 10.1038/s41586-024-08114-4
