The fossil, named 'Navaornis hestiae', dates back around 80 million years to the Mesozoic Era and is remarkably well-preserved, especially its skull. This discovery bridges an evolutionary gap of 70 million years between 'Archaeopteryx', the oldest known bird-like dinosaur from 150 million years ago, and modern birds.
Scientists from the University of Cambridge and the Natural History Museum of Los Angeles County used high-resolution micro-CT scans to digitally reconstruct 'Navaornis''s skull and brain, revealing its unique structure. While the cerebrum was more developed than that of 'Archaeopteryx', indicating advanced cognitive abilities, other brain areas such as the cerebellum were less evolved, suggesting that full flight control capabilities had yet to emerge.
"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," said Dr Guillermo Navalon, co-lead author from Cambridge's Department of Earth Sciences.
The fossil was discovered by William Nava, director of Brazil's Museu de Paleontologia de Marilia, in 2016 in Presidente Prudente. The region, once characterized by slow-flowing creeks, contributed to the exceptional preservation of this specimen.
Professor Daniel Field, senior author of the study, emphasized the importance of this discovery, explaining, "Modern birds have some of the most advanced cognitive capabilities in the animal kingdom... 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."
'Navaornis' belonged to a group of early birds known as enantiornithines, or 'opposite birds,' which split from modern birds over 130 million years ago. Despite its resemblance to a modern pigeon, it was part of a lineage that lacked certain advanced brain features seen in today's avian species.
Dr Luis Chiappe from the Natural History Museum of Los Angeles County noted, "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."
The research published in 'Nature' highlights that 'Navaornis''s unique brain structure offers vital clues about the gradual evolution of bird cognition and behavior, pointing towards adaptations that may have supported complex activities such as foraging and social interactions.
While the researchers acknowledge that 'Navaornis' is only one step toward solving the puzzle of avian brain evolution, it provides critical evidence for understanding the transition between early birds and their modern descendants. Future studies aim to explore more fossils from the same region in Brazil for further insights.
The research received support from UK Research and Innovation (UKRI), and Daniel Field is a Fellow of Christ's College, Cambridge.
Research Report:Cretaceous bird from Brazil informs the evolution of the avian skull and brain
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