One of the most enduring mysteries of vertebrate evolution is how the distinct brains and intellect of contemporary birds developed, and a “one of a kind” fossil discovery could revolutionize our knowledge of this process.
An exceptionally well-preserved fossil bird from the Mesozoic Era, around the size of a starling, has been discovered by researchers. This is one of the most important discoveries of its kind since the entire skull has been preserved nearly intact, which is uncommon for any fossil bird but especially for one so old.
The researchers, lead by the Natural History Museum of Los Angeles County and the University of Cambridge, were able to digitally rebuild the bird’s brain, which they have called Navaornis hestiae, thanks to the remarkable three-dimensional preservation of the skull. Before the catastrophic extinction catastrophe that wiped off all non-avian dinosaurs, Navaornis thrived in what is now Brazil around 80 million years ago.
According to the researchers, their finding, which was published in the journal Nature, may serve as a kind of “Rosetta Stone” for figuring out the evolutionary history of the contemporary bird brain. The fossil closes a 70-million-year gap in our knowledge of the evolution of bird brains between the 150-million-year-old Archaeopteryx, the first known dinosaur that resembled a bird, and modern birds.
Given that its cerebrum was larger than Archaeopteryx’s, Navaornis may have possessed more sophisticated cognitive abilities than the first dinosaurs that resembled birds. But the majority of its brain regions, such as the cerebellum, were underdeveloped, indicating that it had not yet developed the sophisticated flight control systems found in contemporary birds.
According to co-lead author Dr. Guillermo Navalón of Cambridge’s Department of Earth Sciences, “the brain structure of Navaornis is almost exactly intermediate between Archaeopteryx and modern birds – it was one of these moments in which the missing piece fits absolutely perfectly.”
The fossil was found in 2016 at a location in the nearby neighborhood of Presidente Prudente, and Navaornis is named for William Nava, director of the Museu de Paleontologia de Marília in São Paolo State, Brazil. This location was probably a dry region with slowly moving creeks tens of millions of years ago, which allowed for the fossil’s remarkable preservation. Because of its preservation, the researchers were able to recreate the bird’s brain and skull in remarkably detailed detail using cutting-edge micro-CT scanning technology.
“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,” Navalón said.
According to the study’s principal author, Professor Daniel Field of Cambridge’s Department of Earth Sciences, “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.”
The evolutionary transition between the brains of Archaeopteryx and modern birds was essentially unknown prior to this finding. “This represents nearly 70 million years of avian evolution in which all the major lineages of Mesozoic birds originated – including the first representatives of the birds that live today,” Navalón said. “Navaornis sits right in the middle of this 70-million-year gap and informs us about what happened between these two evolutionary points.”
Even though Navaornis’s head initially looks a lot like that of a little pigeon, a closer look shows that it is actually a member of an ancient bird species known as enantiornithines, or the “opposite birds.”
Although “opposite birds” split from contemporary birds about 130 million years ago, they probably had sophisticated feathers and could fly just as well as modern birds. The Navaornis’s brain structure raises a new puzzle, though:how did opposite birds 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 centre?
Field, who is also the Strickland Curator of Ornithology at Cambridge’s Museum of Zoology, stated, “This fossil represents a species at the midpoint along the evolutionary journey of bird cognition.” “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.”
Despite being a major accomplishment, the researchers claim the discovery is just the beginning of their understanding of how avian intelligence evolved. How Navaornis interacts with its surroundings may be revealed by future research, which could assist address more general queries regarding the historical development of bird cognition.
Field’s research team has been describing four Mesozoic fossil birds since 2018, including Janavis, Ichthyornis, and Asteriornis (the “Wonderchicken”). Navaornis is the most recent of these birds. By combining cutting-edge visualization and analytical techniques with new fossil findings, the team has uncovered important new information about the origins of birds, the most varied group of vertebrate animals still in existence.
The study was partially funded by UKRI, or UK Research and Innovation. Daniel Field attends Cambridge’s Christ’s College as a Fellow.
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