The complete skull has been preserved almost intact, which the study highlights makes it one of the most significant finds of its kind.
Navaornis lived approximately 80 million years ago in what is now Brazil, before the mass extinction event that killed all non-avian dinosaurs.
The fossil filled a 70-million-year gap in the understanding of how the brains of birds evolved: between the 150-million-year-old Archaeopteryx, external, the earliest known bird-like dinosaur, and birds living today.
Navaornis 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 were less developed, suggesting that it had not yet evolved the complex flight-control mechanisms of modern birds.
Dr Navalón, from Cambridge’s Department of Earth Sciences, said: “It was one of these moments in which the missing piece fits absolutely perfectly.
“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.”
