Dinosaurs with feathers gave rise to today’s birds – 06/11/2023 – Science

In 1993, the movie “Jurassic Park” helped inspire 9-year-old Stephen Brusatte to become a paleontologist. So Brusatte was excited to advise the producers of last year’s “Jurassic World: Dominion” on what scientists have learned about dinosaurs since he was a child.

He was especially happy to see one of the most important discoveries hit the screen: dinosaurs that had feathers. But judging by the emails he received, some viewers didn’t share his excitement.

“A lot of people thought it was made up,” said Brusatte, a professor at the University of Edinburgh in Scotland. “They thought the filmmakers wanted to do something crazy.”

Far from being crazy, feathered dinosaurs have become accepted fact, thanks largely to a trove of remarkable fossils that have been unearthed in northeast China since the mid-1990s. Now Brusatte and other paleontologists are trying to determine exactly how these dinosaurs got to be flight and became the birds that fly today—an evolutionary mystery that spans more than 150 million years.

The first major clue to the origin of birds came in 1861, when quarry workers in Solnhofen, Germany, found a spectacular fossil of a 145-million-year-old bird that came to be called Archaeopteryx. It had feathery wings like living birds, but it also had features found in reptiles, such as teeth, claws, and a long bony tail.

In the 1970s, John Ostrom, a paleontologist at Yale University, identified similarities in the skeletons of birds and land-dwelling dinosaurs called theropods, a group that includes Velociraptor and tyrannosaurus rex. But no theropod fossils have preserved wings, let alone feathers. Without further evidence, Ostrom and other paleontologists have been excitedly discussing the origin of birds for decades.

In 1996, Pei-ji Chen, a paleontologist at the Institute of Geology and Paleontology in Nanjing, China, attended a paleontology meeting at the American Museum of Natural History in New York, where he handed a package of photographs to Ostrom.

The photos showed a dinosaur fossil with a fringe that appeared to be rudimentary feathers. Ostrom was so surprised that he had to sit down.

The 125-million-year-old fossil, now known as Sinosauropteryx prima, came from Liaoning province in northeast China. It has been exquisitely preserved in a Pompeii-like ash blanket. Since then, a steady stream of feathered dinosaur fossils has surfaced in the region.

“There are many thousands of dinosaurs with feathers today,” said Brusatte.

As more fossils emerged, paleontologists realized that theropods weren’t the only dinosaurs with feathers. Other species had simple versions, more like threads than the complex network of interlocking filaments found in bird feathers today.

Around 160 million years ago, theropods exploded into a bizarre mix of feathery shapes. Julia Clarke, a paleontologist at the University of Texas, and her colleagues studied fossils discovered in China’s Hebei province of a striking and bizarre species called caihong juji. Fossilized pigments in the feathers suggest that its body was black, while its head and shoulders were a veritable rainbow.

It’s hard to figure out how the caihong juji wore its feathers. Modern birds have asymmetrical wing feathers that help direct airflow to generate lift. But caihong juji it had asymmetrical feathers only on the tail.

Theropods may have initially used their feathers to generate lift while running. This ability may have allowed them to climb slopes more quickly or even climb up the sides of trees. Dinosaurs with feathers like caihong juji they didn’t have the muscles to fly like birds, but they may have leapt and glided in ways that scientists haven’t yet figured out.

“These organisms are just weird, and I think they defy our logic,” said Jingmai O’Connor, a paleontologist at the Field Museum in Chicago.

Feathered dinosaurs were more than just intermediaries on the way to birds as we know them. They have survived for tens of millions of years. “They were clearly good at whatever they did,” Clarke said.

Archeopteryx belonged to a branch of the dinosaur tree that later adapted to fly greater distances. But paleontologists are still divided on how well it could fly. Although it had asymmetrical feathers on its wings, it lacked a breastbone that could anchor powerful flight muscles.

Later, about 130 million years ago, the first birds split into two main branches, which independently evolved into powered fliers. The lineage that gave rise to all living birds is known as the ornithuromorphs. But it was the other branch, called enantiornithines, that dominated the skies for tens of millions of years.

On a superficial level, enantiornithines look a lot like today’s birds. But O’Connor and his colleagues are discovering a lot of strange biology inside them.

Live birds, for example, are usually born without feathers or with just fuzzy down, and then their feathers grow all over their bodies. They gradually molt as adults, so they never lose the fur that keeps their bodies warm.

But enantiornithine birds seem to have developed feathers in a radically different way, as O’Connor and his colleagues argued in a recent study. They hatched with naked bodies but fully feathered wings. As they matured, feathers grew on their bodies. But as adults, they shed their body feathers all at once. Until their new feathers grew, they had to survive without insulating plumage.

This lineage of birds survived until 66 million years ago, when an asteroid hit Earth. About three-quarters of the planet’s species went extinct, including all feathered dinosaurs except the ornithuromorphs.

O’Connor and other paleontologists are investigating why these birds survived when all other feathered reptiles disappeared. Debris from the impact caused widespread wildfires, followed by darkness and falling temperatures. Earth’s ecosystems collapsed. Feathered dinosaurs that ate leaves or small animals may have starved to death. But the birds evolved beaks that allowed them to eat the vast amounts of seeds buried in the ground.

O’Connor thinks other factors may also be at play. After thriving for 70 million years or more, enantiornithines may have suddenly become vulnerable in the cold climate after the asteroid, when they shed all their feathers at once.

“You throw them in an impact winter, where global temperatures have dropped and there are resource shortages, it just pushes them over the edge,” O’Connor said.

^{Translated by Luiz Roberto M. Gonçalves}