New Feathered Dinosaur Had Four Wings but Couldn't Fly
圖片附件: Serikornis sungei .jpg (2017-8-30 01:47 AM, 139.7 K)
A pheasant-size dinosaur found in China is causing a stir among scientists trying to understand the origins of flight.
The newly named species, Serikornis sungei, adds to the ranks of dinosaurs that effectively had four wings, thanks to heavily feathered hindlimbs and forelimbs. But in a twist for paleontologists, the evidence suggests that Serikornis couldn’t fly.
“The feathering of Serikornis shows for the first time a complete absence of barbules—that is, the microstructures that allow feathers to resist air pressure during wing beats,” says study leader Ulysse Lefèvre, a paleontologist at the Royal Belgian Institute of Natural Sciences in Brussels. “The plumage is composed of four wings, as with many theropod dinosaurs from China, but it did not allow ‘Silky’ to take off from the ground or from a tree.”
Instead, Lefèvre and his team suggest that Serikornis was part of a subgroup of early four-winged dinosaurs that had feathers not well adapted for flight. Rather than flapping or even gliding through the trees, these animals would have likely spent their lives scampering around on the forest floor.
Found in 2014, the Serikornis fossil is about 160 million years old, the team reports this month in the journal The Science of Nature. The fossil hails from China’s northeastern Liaoning Province, a region famous for preserving the remains of early birds and feathered dinosaurs. (Read about a museum exhibit that recently showcased dinosaurs in all their feathered glory.)
The first four-winged dinosaur, Microraptor, was discovered in Liaoning in 2000. And the same rock layer Serikornis came from previously yielded the four-winged species Aurornis and Anchiornis. As more multi-winged discoveries popped up, many scientists began to see the arrangement as an important precursor to full powered flight in birds, with these early bird relatives either flying or gliding between the branches of China’s prehistoric forests.
Lefèvre and his team named the new species in honor of Sun Ge, the scientist at the Paleontological Museum of Liaoning who made the fossil available for study, and for the presumed silky texture of its body covering. Serikos means “silk” in ancient Greek.
In life, the newly described dinosaur would have been about 1.5 feet long with tiny, sharp teeth and a body covered in downy, wispy feathers. Its limbs, however, would have sported several other kinds of feathers, including long pennaceous feathers with central vanes that are more like the plumage we often see on modern birds. (See rare dinosaur-era bird wings found trapped in amber.)
That’s what makes Serikornis such a puzzle. According to Lefèvre, the dinosaur’s wing feathers simply weren’t light and stiff enough to produce enough thrust to counteract gravity. Instead, he suspects the animal used its feathers for insulation and as a display to fend off rivals or woo mates.
Tripping Over Trousers?
The discovery adds to our growing knowledge of the diversity of feathered dinosaurs, which used their plumage for many purposes other than flight, says Thomas R. Holtz, a paleontologist at the University of Maryland in College Park.
“We aren't running out of new types of feathered Jurassic and Cretaceous dinosaurs and can look forward to continued new discoveries,” he says. (Also see a baby bird from the time of the dinosaurs found fossilized in amber.)
The long feathers on this dinosaur’s legs and feet are traits shared with many early birds and feathered dinosaurs, Holtz adds. “Such feathers might be used to help steer in flying members of the group, but in the case of this non-flier, they must have had some other function.”
However, not everyone agrees that Serikornis couldn’t fly. Mike Benton, a paleontologist at the University of Bristol in the U.K., thinks the case for this dinosaur as a ground-dweller is not strong.
“The hind wings would be inconvenient for a ground-runner,” says Benton. “The long feathers on the thigh and calf would be like very elaborate bell-bottomed trousers, rubbing and catching as the animal walked or ran."
He still prefers the interpretation that the four-winged arrangement is “a model for the origin of flight, in which early dinosaurs such as Serikornis clambered into trees, perhaps chasing insects and other small tree-dwellers for food. To escape predators or to get around, they would glide from bough to bough.”
Lefèvre concedes it’s possible these little dinosaurs could parachute to the ground from the trees—but that’s still a far cry from flight. “The plumage of Silky does not allow it to perform modern flight but can surely help slow its descent,” he says.
Along with its close relatives, Serikornis also had enlarged claws that may have allowed it to scramble up tree trunks, Lefèvre adds, noting this “remains a tricky issue and requires more time and fossils to better understand.”
The Serikornis sungei fossil, which shows its varied plumage..jpg (2017-8-30 01:47 AM, 149.25 K)