Brazil's 'Unik' Skull Fossil Reveals Bird Brain Evolution

Bird illustration. (Unsplash/Mark Olsen)

JAKARTA - Today's bird brain facilitates the level of cognitive skills and behavioral complexity that mammals can only compete with.

However, how the bird's brain evolved for millions of years from the form of ancestral dinosaurs has long confused scientists. Now, it has changed thanks to the spectacular discovery of fossils in Brazil.

The researchers dug the skull of a bird species the size of an previously unknown star named Navaornis hestiae, which was so well preserved that they could digitally reconstruct the anatomy of the brain and its inner ear based on the shape of the brain.

The bird inhabited a arid neighborhood about 80 million years ago during the Cretaceous Period, the last era of the dinosaur era.

"This discovery is unique," said Cambridge University paleontology Guillermo Navalman, one of the lead authors of the study published in the middle of this month in the journal Nature.

Birds evolved from small-haired dinosaurs during the Jurassic Period. Navaornis' discovery filled a 70 million-year void in understanding the neuroanatomic evolution of birds, which stems from the earliest known bird, Archaeoptylix, which lived in Europe about 150 million years ago.

Navaornis skull, with modern geometry in terms of a large beak shape and eye cavity, looks like a small pigeon. His brain shows a combination of modern, ancient, and some of them.

"This is a long sought-after evidence because the 3D skull of a well-preserved ancient bird - which flies over the head of a dinosaur - is extremely rare, and this one is well preserved," said the paleontologist of the Los Angeles County Natural History Museum and lead author of the study Luis Chiappe.

While the University of Cambridge paleontologist and study senior author Daniel Field said, "Illustrators have struggled to understand how and when unique brains and extraordinary bird intelligence evolved. This field has been waiting for the discovery of fossils exactly like this."

His name means "AVA bird," taken from William Nava, the scientist who discovered the fossil in 2016 in the southeastern Brazilian state of Sao Paulo.

Navaornis was among a group of birds called antiornithines that developed rapidly during the Cretaceous Age, but went extinct in the impact of asteroids 66 million years ago that destroyed dinosaurs, but saved a rapidly growing bird lineage to date. That means Navaornis is not the progenitor of today's birds, and its modern-looking characteristics evolve separately from the characteristics of today's birds.

She is sleek and smooth, showing she eats insects and seeds that she can swallow intact. She coexists with long-necked plant-eating dinosaurs and large meat-eating dinosaurs.

"A little bit, it may look very much like a live bird. However, closer inspections may reveal some ancient traits that do not exist in live birds, such as clawing that stands out from the wings," Field said.

Navaornis' brain - measuring about four-tenths of inches (10 mm) - is smaller, relative to the size of the skull, compared to modern birds, but larger and more complex than in Archaeopteryx.

His small brain, the brain structure of live birds, helps coordinate motor control during flight, smaller than in today's bird species and is more like Archaeoptylix.

However, the brain is connected to the spinal cord in a way similar to modern birds and in this case, humans and unlike Archaeopteryx and dinosaurs that came from birds.

His brain has several characteristics that are a transition between Archaeoptylix and modern birds. The size and brain shape between the two, the existing bird's structure containing the area involved in the complex cognition, shows that his brain is more cognitively advanced than the earliest birds, but less advanced than today's birds.

Navaornis shows some unique characteristics such as a vestibular device, an equilibrium organ in the inner ear, which is larger than any other known bird.

"There is a significant gap (in the fossil record) between birds like Archaeopteryx which has a more dinosaur-like type of brain and birds closely related to modern birds," Chiappe said.

"The new evidence documents the phase of the transition in brain evolution but with some unexpected specializations that may be related to functional properties such as flying," he added.

It is known that well-preserved fossils from the early stages of the evolution of birds are rare. The fragility of the birds' bones makes their fossils rare. This skull is preserved three-dimensional, not evenly destroyed like many other fossils. The fossil, which includes 80 percent of the bird's skeleton, shows it is a competent pilot.