In 1993, “Jurassic Park” inspired 9-year-old Stephen Brusatte to become a paleontologist. So dr. Brusatte was pleased to advise the producers of last year’s “Jurassic World: Dominion”. about what scientists had learned about dinosaurs since he was a kid.
He was especially happy when he saw one of the most important discoveries appear on the silver screen: dinosaurs with feathers. But judging by the emails he’s received, some moviegoers didn’t share his excitement.
“A lot of people thought it was made up,” says Dr. Brusatte, a professor at the University of Edinburgh. “They thought it was filmmakers trying to do something crazy.”
Far from crazy, feathered dinosaurs have become an established fact, thanks in large part to a trove of remarkable fossils unearthed in northeast China since the mid-1990s. Now try dr. Brusatte and other paleontologists determined exactly how feathered dinosaurs achieved powered flight and became the birds of flight 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 called Archeopteryx.. It had feathered wings like living birds, but also had features found in reptiles, such as teeth, claws, and a long bony tail.
Charles Darwin, who had published “On the Origin of Species” two years earlier, was delighted. Archeopteryx looked as Darwin would have predicted if birds had evolved from reptilian ancestors. “It’s a big thing for me,” he told a friend.
As grand as it may be, Archeopteryx hasn’t closed the case. For example, it didn’t reveal what group of reptiles birds evolved from, nor how those ancestors evolved wings out of nowhere.
In the 1970s, John Ostrom, a paleontologist at Yale University, identified similarities in the skeletons of birds and ground-walking dinosaurs called theropods, a group that includes Velociraptor. And the Tyrannosaurus rex. But no theropod fossils have preserved wings, let alone feathers. Without further evidence, Dr. Ostrom and other paleontologists have had fierce debates about the origin of birds for decades.
In 1996, Pei-ji Chen, a paleontologist from the Nanjing Institute of Geology and Paleontology in China, came to a paleontology meeting at the American Museum of Natural History in New York, where he presented a package of photographs to Dr. Ostrom.
The photos showed a dinosaur fossil with a fringe of what appeared to be rudimentary feathers. Dr. Ostrom was so amazed he had to sit down.
The 125 million year old fossil, now known as Sinosauropteryx prima, came from Liaoning province in northeastern China. It was beautifully preserved in a Pompeii-like blanket of ash. Since then, a steady stream of feathered dinosaur fossils have surfaced from the region.
“There are now many thousands of feathered dinosaurs,” said Dr. 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.
Paleontologists now suspect that the ancestor of all dinosaurs had feathers. And recent discoveries indicate that feathers predated dinosaurs.
Dinosaurs’ closest relatives were pterosaurs, which flew like bats with membranes extending from their hands to their sides. It turned out that they also had simple feathers.
The first simple springs originally served as insulation. The largest dinosaurs may have been able to use the large volume of their bodies to retain heat, which is why they seem to have lost feathers – just as elephants lost most of their hair.
In contrast, theropods evolved more elaborate feathers. Some resembled fluffy down. Others developed complex feathers that could form blades – the first wings.
Theropods couldn’t use their early wings for flight. Some horse-sized species had wings the size of laptop screens. Dr. Brusatte speculated that dinosaurs used these more elaborate feathers as displays during courtship.
160 million years ago, theropods had exploded into a bizarre menagerie of feathery forms. Julia Clarke, a paleontologist at the University of Texas, and her colleagues have been studying fossils discovered in China’s Hebei province of a stunning and bizarre species called Caihong juji. Fossilized pigments in the feathers suggest its body was black, while its head and shoulders were an iridescent rainbow.
It’s hard to figure out how Caihong juji used his feathers. Modern birds have asymmetrical feathers on their wings, which help direct airflow to generate lift. But Caihong juji only had asymmetrical feathers on his tail.
Theropods may have initially used their feathers to generate lift while running. That ability would have allowed them to climb slopes faster or even scale the sides of trees. Feathered dinosaurs like Caihong juji lacked the muscles for powered flight like birds, but they might have jumped and slid in ways scientists have yet to figure 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 intermediates on the path to birds as we know them. They have survived tens of millions of years. “They were clearly good at whatever they were doing,” said Dr. Clarke.
Archeopteryx belonged to a branch of the dinosaur tree that later adapted to fly longer distances. But paleontologists are still divided on how well it could fly. Although Archeopteryx had asymmetrical feathers on its wings, it lacked a sternum to anchor powerful flight muscles.
Later, about 130 million years ago, early birds split into two major branches, both of which evolved independently into powered fliers. The lineage that gave rise to all living birds is known as the ornithuromorphs. But it was the other branch, called the enantiornithines, that dominated the sky for tens of millions of years.
On the surface, enantiornithines are much like birds today. But dr. O’Connor and her colleagues discover a lot of strange biology in them.
For example, live birds are usually born with no feathers or just a downy down, and then grow their feathers all over their bodies. They gradually molt feathers as adults so they never lose the fur that keeps their bodies warm.
But enantiornithic birds seem to have evolved feathers in a radically different way, as Dr. O’Connor and her colleagues argued in a recent study. They emerged with bare bodies but fully feathered wings. As they grew older, they acquired plumage on their bodies. But as adults, they molt their body feathers all at once. Until their new feathers grew in, they had to manage without their insulating plumage.
This line of birds survived until 66 million years ago, when an asteroid hit Earth. About three-quarters of all species on the planet were wiped out, including all feathered dinosaurs except the ornithuromorphs.
Dr. O’Connor and other paleontologists are investigating why those birds survived when all other feathered reptiles disappeared. The debris from the impact sparked widespread wildfires, followed by darkness and a plunge in temperatures. Terrestrial ecosystems collapsed. Feathered dinosaurs that ate leaves or small animals may have starved. But birds had evolved beaks that allowed them to eat the vast quantities of seeds buried in the ground.
Dr. O’Connor thinks other factors also played a role. Having thrived for 70 million years or more, enantiornithines may have suddenly become vulnerable in the post-asteroid cold weather when they molted all their feathers at once.
“You throw them into a harsh winter, where global temperatures are now down and there’s a scarcity of resources, it’s just going to push them over the edge,” said Dr. O’Connor.