An extraordinarily preserved fossil bird from Brazil has allowed scientists to reconstruct the brain of a bird that lived alongside the dinosaurs. The 80-million-year-old skull of Navaornis hestiae fills a crucial evolutionary gap between Archaeopteryx and modern birds — and reveals that the modern bird brain evolved in stages.

Birds are dinosaurs.

More precisely, they are the only surviving lineage of dinosaurs — descendants of small feathered theropods that survived the mass extinction 66 million years ago.

During that enormous evolutionary journey, something remarkable happened to their brains.

Modern birds possess sophisticated visual systems, extraordinary navigational abilities and, in some species, levels of problem-solving and tool use that rival those of mammals.

But scientists have struggled to understand when the distinctive modern bird brain appeared.

A spectacular fossil from Brazil is now providing part of the answer.

Researchers led by the University of Cambridge and the Natural History Museum of Los Angeles County have digitally reconstructed the brain of an approximately 80-million-year-old bird named Navaornis hestiae.

A skull preserved in three dimensions

The discovery is exceptional because bird skulls are extraordinarily fragile.

Their bones are thin and lightweight — an evolutionary advantage for flight, but a major disadvantage for fossilisation.

Most ancient bird skulls have been crushed, flattened or destroyed.

Navaornis is different.

Its skull survived in remarkably complete three-dimensional preservation.

The fossil was discovered in Brazil in 2016 by palaeontologist William Nava, after whom the new species was named.

Researchers could therefore examine its internal structure without destroying it.

Reconstructing a brain that disappeared 80 million years ago

The actual brain, of course, is long gone.

But the brain once occupied the space inside the skull.

Using high-resolution micro-CT scanning, scientists could digitally map that internal cavity.

From these data they produced a three-dimensional reconstruction of the brain and inner ear.

The technique effectively created a virtual cast of the animal’s brain.

For palaeontologists, this is extraordinarily valuable.

The shape of the brain can reveal information about an extinct animal’s senses, behaviour and evolutionary relationships.

Between Archaeopteryx and modern birds

Until this discovery, scientists faced a frustrating gap in the fossil record.

At one end was Archaeopteryx, which lived around 150 million years ago and possessed a comparatively dinosaur-like brain.

At the other were modern birds, with their highly specialised neurological anatomy.

There were few sufficiently well-preserved fossils showing what happened in between.

Navaornis occupies part of that missing evolutionary territory.

Its brain was neither simply dinosaur-like nor completely modern.

Instead, it contained a mosaic of ancient and surprisingly modern features.

A modern-looking cerebrum

One of the most striking findings concerned the cerebrum.

In modern birds this region is greatly enlarged and associated with sophisticated sensory processing and cognition.

The cerebrum of Navaornis was already expanded in a way that approached the condition seen in living birds.

That suggests an important part of the architecture associated with modern avian brains had already evolved by around 80 million years ago.

But another important region told a different story.

The cerebellum had not caught up

The cerebellum plays an important role in movement, balance and the coordination of complex behaviour.

In Navaornis, this region was less developed than in modern birds.

The combination is revealing.

It indicates that the modern bird brain did not appear as a single evolutionary package.

Different parts changed at different times.

The cerebrum had already become relatively modern while other neurological structures retained more ancestral characteristics.

A bird with teeth

Navaornis belonged to a group of prehistoric birds called the enantiornithines.

They were enormously successful during the Cretaceous Period and lived across much of the world.

To modern eyes, Navaornis would have looked recognisably bird-like.

But there was one particularly unmodern feature hidden inside its mouth:

it had teeth.

Enantiornithines belonged to an evolutionary branch separate from the lineage that ultimately produced today’s birds.

They survived for tens of millions of years before disappearing in the mass extinction at the end of the Cretaceous.

How intelligent was Navaornis?

The fossil cannot tell us exactly how intelligent the animal was.

Brain shape alone cannot provide an IQ test for an extinct species.

But its anatomy shows that some of the neurological reorganisation characteristic of living birds occurred surprisingly early.

Professor Daniel Field of Cambridge’s Department of Earth Sciences described the discovery as bringing scientists closer to understanding the evolutionary transition between the brains of Archaeopteryx and those of living birds.

The finding also demonstrates why exceptional fossils can fundamentally change our picture of evolution.

A single well-preserved skull can contain information that thousands of incomplete skeletons cannot provide.

Evolution does not build everything at once

Navaornis illustrates an important principle of evolution.

Complex biological systems do not necessarily appear fully formed.

Different components can evolve at different speeds.

The wings of birds changed.

Their skeletons became lighter.

Their tails shortened.

Their teeth eventually disappeared.

And inside their skulls, different regions of the brain were simultaneously following their own evolutionary trajectories.

The modern bird brain was assembled gradually.

The dinosaur looking through your window

Today there are more than 10,000 living bird species.

Crows solve puzzles.

Parrots learn words.

Pigeons navigate over enormous distances.

Owls process extraordinary amounts of visual and auditory information.

All of those abilities are products of a neurological history extending deep into the age of dinosaurs.

Navaornis hestiae provides a rare snapshot from the middle of that transformation.

Eighty million years ago, while giant dinosaurs still walked across the planet, a small bird was already flying above South America with a brain containing some surprisingly modern characteristics.

Its lineage eventually disappeared.

But its skull survived.

And inside that fossilised skull remained the imprint of a brain that is helping scientists reconstruct how dinosaur cognition ultimately became the remarkable intelligence of modern birds.

Source: Based on “Bird brain from the age of dinosaurs reveals roots of avian intelligence,” published by the University of Cambridge on 13 November 2024. The research was led by scientists from Cambridge and the Natural History Museum of Los Angeles County. The underlying study on Navaornis hestiae was published in Nature on 13 November 2024.