In 2016, palaeontologist William Nava made a remarkable discovery. He unearthed a small fossil that may unlock the secrets behind the evolution of modern birds’ complex brains and intelligence – one of the most enduring mysteries of vertebrate history.
According to new research, the fossilised bird – named Navaornis hestiae – lived around 80 million years ago during the Mesozoic Era, in what is now Brazil.
Comparable in size to a starling, the skull is preserved in near-perfect three-dimensional form – an extraordinary rarity, especially for such an ancient species.
This preservation has enabled researchers from the University of Cambridge and the Natural History Museum of Los Angeles County to reconstruct the bird’s brain digitally, offering groundbreaking insights into how bird cognition evolved.
“One-of-a-kind” fossil
The work, published in Nature, reveals that Navaornis could be the missing piece for understanding the origins of modern avian intelligence.
Filling in a 70-million-year gap between the earliest known bird-like dinosaur, Archaeopteryx, and today’s birds, the fossil sheds light on how birds’ brains gradually developed.
According to the researchers, Navaornis has a larger cerebrum than Archaeopteryx, indicating advanced cognitive abilities; but other brain structures, such as the cerebellum, remain less developed. This suggests Navaornis had not yet evolved the sophisticated flight control seen in today’s birds.
“The brain structure of Navaornis is almost exactly intermediate between Archaeopteryx and modern birds,” says Dr. Guillermo Navalón, co-lead author from Cambridge’s Department of Earth Sciences. “It was one of these moments in which the missing piece fits absolutely perfectly.”
Into the brain
Using cutting-edge micro-CT scans, the researchers meticulously reconstructed the bird’s skull and brain, unveiling remarkable details of its internal structure.
“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,” Navalón says.
Professor Daniel Field, senior author of the study, explains the significance of the discovery: “Modern birds have some of the most advanced cognitive capabilities in the animal kingdom, comparable only with mammals. 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.”
Belonging to an ancient group of birds known as enantiornithines, or ‘opposite birds,’ Navaornis diverged from modern birds over 130 million years ago.
Although at first glance its skull resembles that of a small pigeon, closer examination reveals that Navaornis is distinctly primitive. Unlike modern birds, it lacks the expanded cerebellum that supports spatial awareness in flight. How, then, did it manage the coordination required for flight? This question adds a new layer of intrigue to the evolutionary puzzle.
“This fossil represents a species at the midpoint along the evolutionary journey of bird cognition,” says Field. “Its cognitive abilities may have given Navaornis an advantage when it came to finding food or shelter, and it may have been capable of elaborate mating displays or other complex social behaviour.”
What's next?
While Navaornis is one of the most significant Mesozoic bird fossils discovered, the researchers hope additional discoveries at the Brazilian site could provide further insights into avian evolution.
“This might be just one fossil, but it’s a key piece in the puzzle of bird brain evolution,” Field says. “With Navaornis, we’ve got a clearer view of the evolutionary changes that occurred between Archaeopteryx and today’s intelligent, behaviourally complex birds like crows and parrots.”
Despite this breakthrough, the team sees Navaornis as only the first step towards understanding the evolution of bird cognition. The fossil is part of a recent lineage of discoveries, including Ichthyornis, Asteriornis, and Janavis, by Field’s research group, whose findings continue to reveal new perspectives on the origins of the world’s most diverse vertebrate class: birds.
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