Cosmos
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By Cosmos
A remarkably well-preserved fossil skull of a bird which lived 80 million years ago has been discovered in Brazil. It fills a 70-million-year gap in our understanding of how bird brains evolved.
The bird belongs to a newly described species called Navaornis hestiae. The finding is reported in a paper published in Nature.
The earliest bird-like dinosaur is Archaeopteryx. It lived 150 million years ago.
Navaornis has a larger cerebrum than Archaeopteryx, suggesting more advanced cognitive abilities than the earliest bird-like dinosaurs.
Most areas of its brain were less developed than in modern birds, indicating that Navaornis had not yet evolved the complex flight control mechanisms of today’s feathered friends.
“The brain structure of Navaornis is almost exactly intermediate between Archaeopteryx and modern birds,” says co-lead author Dr. Guillermo Navalón from the University of Cambridge, UK. “It was one of those moments in which the missing piece fits absolutely perfectly.”
Navaornis was discovered in 2016 near the city of Presidente Prudente, about 500km west of São Paulo.
The region 80 million years ago, during the Cretaceous period, was probably relatively dry with slow-flowing creeks.
Micro-CT scanning was used to reconstruct the bird’s skull cavity in remarkable detail.
“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,” says Navalón.
Today, birds have some of the most advanced cognitive abilities in the animal kingdom. Corvids – such as crows, ravens and magpies – are well established problem solvers.
But scientists have long sought to understand how this intelligence developed over millions of years. Very little evidence about this transition has been found, however, linking Archaeopteryx to its modern descendants – until Navaornis.
The ancient bird is a member of a group named enantionithines – or “opposite birds”. This name was coined by palaeontologist Cyril A. Walker in 1981 due to the reversed articulation between the shoulder blade and a bone called the coracoid compared with other avian groups.
“Opposite birds diverged from modern birds more than 130 million years ago, but had complex feathers and were likely competent flyers like modern birds,” says senior author of the new research Daniel Field, a professor at Cambridge. “However, the brain anatomy of Navaornis poses a new question: 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?”
Despite this, Navornis was no dim wit.
“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,” Field adds.
The Navornis fossil is one of the best bird fossils found from the Mesozoic era – also known as the “Age of Dinosaurs”. The palaeontologists are hopeful the site in Brazil and other locations around the world will further illuminate how birds evolved their smarts over the aeons.
