🐦‍⬛ The Rosetta Stone of bird evolution

Hello! Welcome to another edition of the Brazil Society newsletter! This week: the story of how a fossil found in São Paulo revolutionized the field of paleontology. Enjoy! 

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The Brazilian fossil that bridged a gap of 70 million years

The scientific community has known, for some time, that our modern birds evolved from dinosaurs, such as the well-known Archaeopteryx, which lived around 150 million years ago in the Late Jurassic period. But until very recently, paleontologists had no idea how one group evolved into another. 

This all changed thanks to a fossil found in southeastern Brazil.

Birds are some of the most cognitively advanced animals on the planet, with brains uniquely specialized for flight, complex behaviors and even problem-solving. Archaeopteryx, meanwhile, had a comparatively primitive brain, large enough to fly but not much beyond that.

But a paper published in October last year in the scientific journal Nature describes the finding of what appears to be the missing evolutionary link between bird-like dinosaurs and the bird species of today, bridging a gap of 70 million years in understanding how bird brains came to be.

The paper centers around the discovery of a prehistoric bird fossil in 2016, found by self-taught paleontologist William Nava, from the state of São Paulo.

“Weird brains”

The bones of the starling-sized animal, named Navaornis hestiae, were uncovered at a paleontological site near Presidente Prudente, a city far west of São Paulo state. 

While several bird fossils from the Mesozoic period have been found before, few are dug up in such excellent condition, as explained by Guillermo Navalón, a paleontologist at the Department of Earth Sciences of the University of Cambridge, and one of the study’s lead authors.

“Bird bones are generally very fragile, and the fossils we had found for about half of birds’ evolutionary history were very fragmented or flattened,” he told The Brazilian Report. “That’s OK when studying things like feathers and color patterns, but they fail to tell us about aspects that require three-dimensional preservation, and that’s where Navaornis comes in.”

Complete three-dimensional bird skull fossils like Navaornis are incredibly rare and gave scientists the ability to bridge an evolutionary gap between primitive avian dinosaurs and what Navalón calls the “really weird brains” of modern birds.

“Their brains are globular, similar to mammals and primates, while the brains of reptiles and most dinosaurs were tubular in shape.”

The study’s authors hailed the discovery of Navaornis as something of a Rosetta Stone for understanding avian intelligence.

Paleontologists affirm that Navaornis lived around 88 million years ago, at the end of the Cretaceous period, and would have lived alongside the groups that evolved into modern birds of today.

But after the famous Cretaceous-Paleogene mass extinction event of around 66 million years ago, modern birds survived, while Navaornis disappeared — along with all non-avian dinosaurs.

The most widely accepted hypothesis is that the dinosaurs were wiped out by a massive asteroid that hit Earth at the end of the Cretaceous period, causing something of a period of Armageddon. “What we know from the fossil record of pollen is that global forests collapsed completely during this time, and there weren’t many plants for hundreds of thousands of years,” explained Navalón.

“The hypothesis we have is that Navaornis lived predominantly in trees, while the group that modern birds originated from was predominantly aquatic, being able to survive in a world without plants.”

A fossil hunter’s paradise

Experts like Navalón agree that Brazil is “one of the most privileged countries for paleontology” today, with a number of recent discoveries besides Navaornis shaping the way the scientific community understands the Earth’s prehistory.

“It reminds me of China in the early 2000s,” said Navalón. “A treasure trove of spectacular fossils that changed how we think about the evolution of loads of groups, particularly during the age of dinosaurs.”

“And Brazil has lots of brilliant young people in the field who will go on to do some really transformative work.”

Among the trailblazers in that regard is William Nava himself, responsible for finding the Navaornis fossil, which ended up being named after him. As an amateur paleontologist for years, he now maintains and curates the fossil collection at the Paleontology Museum of Marília, in the São Paulo city of the same name. 

“Nava has been instrumental for paleontologists in Brazil, and he’s found some crazy fossils himself,” explained Navalón. “Navaornis is named after him, which we thought was the best way to honor him and his work.”