A number of tiny, bat-winged dinosaurs flew the Jurassic skies, according to the strongest evidence yet for such creatures—a well-preserved fossil of a starling-size fluffball that may have looked a little like a flying squirrel. The find, recovered near a farming village in northeastern China, suggests dinosaurs were experimenting with several methods of flight during this period, but many were an evolutionary dead end.
“This fossil seals the deal—there really were bat-winged dinosaurs,” says Stephen Brusatte, a paleontologist at the University of Edinburgh who was not involved with the study.
Scientists were already confident that a number of dinosaurs could fly. There are birds, of course, which are technically dinosaurs and appeared during the Jurassic period, at least 150 million years ago. Other dinosaurs sported feathers on their hind- and forelimbs, effectively giving them four birdlike wings.
Then, in 2015, researchers discovered a dinosaur that may have flown more like a bat. Named Yi qi (Mandarin for “strange wing”) and discovered in northwestern China, the crow-size creature appeared to have a flap of skin stretched between its body and arm bones that was supported by a rod of cartilage. But the fossil, which belongs to an enigmatic group of dinosaurs called the scansoriopterygids, was partial and poorly preserved, so scientists couldn’t be sure it actually flew like a bat. “There’s been debate about whether the skin flap was really an airfoil or used for another purpose,” Brusatte says.
The new fossil, named Ambopteryx longibrachium (meaning “both-wing” and “long arm,” referring to this second method of dinosaur flight) and dated to about 163 million years ago during the Jurassic period, doesn’t have that problem. Nearly every part of the little dino—which was uncovered by a farmer who provides the fossils he finds to the Chinese Academy of Sciences’s Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) in Beijing—is well-preserved, including membranous batlike wings similar to those of Yi qi. “You could have fit it in your hand,” says IVPP paleontologist and study author Jingmai O’Connor. “It would have been this tiny, bizarre-looking, buck-toothed thing like nothing alive today.”
Even Ambopteryx’s stomach contents were preserved. Researchers recovered pieces of bone and small rocks called gastroliths, which modern birds use to grind plant material, indicating the species may have been omnivorous. Though the creature was replete with feathers, these were a downy fuzz and not used for flight. O’Connor also speculates that males of the species may have sported long ornamental tail feathers, possibly to woo females, as can be seen in other scansoriopterygid fossils.
The complete skeleton has allowed scientists to make the first detailed analysis of differences in wing design and mode of flight between these dinosaurs and birds. Researchers measured the bones of the arms and fingers in each type of wing and compared them using statistical methods.
Ambopteryx’s wings were formed by elongating the humerus and ulna, the bones of the upper and lower arm in humans, the team reports today in Nature. Birds instead achieved flight by elongating their metacarpals, analogous to our fingers. “The main lift-generating surface of birds’ wings is formed by feathers,” O’Connor explains. “In bats, pterosaurs [dinosaur-era reptiles that flew similar to bats], and now scansoriopterygids—you instead have flaps of skin that are stretched out in between skeletal elements.”
“This new discovery shows Yi qi was not an aberrant species, but that there was an entire group of bat dinosaurs taking to the skies in the [Jurassic],” says Darla Zelenitsky, a paleontologist at the University of Calgary in Canada who has studied feathered dinosaurs.
However, although nearly 10,000 species of birds live today, no scansoriopterygids survived past the end of the Jurassic. That suggests their early experiment in flight was far less successful, O’Connor says. Still, she says, their existence is remarkable, given that flight has only evolved in a handful of groups of animals across the entire history of life. “The idea that flight evolved more than once in dinosaurs is incredibly exciting and hasn’t quite sunk into the scientific community yet.”
“The evolution of flight wasn’t a gradual march from dinosaur to bird,” Brusatte adds. “It involved lots of experimentation and tinkering.”