More than 160 million years ago, the forests of ancient China were home to a bizarre predator: a tiny dinosaur that glided from tree to tree with leathery, bat-like wings. The newfound fossil, unveiled today in the journal Nature, is just the second feathered dinosaur found with signs of large membranes on its wings. Fitting, then, that the animal's newly assigned genus name is Ambopteryx: Latin for “both wings.”
“The most exciting thing, for me, is that it shows that some dinosaurs evolved very different structures to become volant,” or capable of some form of flight, says lead study author Min Wang, a paleontologist at China's Institute of Vertebrate Paleontology and Paleoanthropology.
Ambopteryx is now the best known fossil of a scansoriopterygid (scan-soary-OP-teh-rigid), an oddball group of nonavian dinosaurs that includes Yi qi, the first dinosaur ever found with bat-like wings. That fossil find—announced in 2015 by study coauthor Xing Xu, the IVPP's deputy director—reshaped how scientists understood the evolution of flight.
“Before the discovery of Yi qi, every flying dinosaur we found, we tried to fit on one evolutionary lineage toward birds,” says study coauthor Jingmai O'Connor, an IVPP paleontologist who specializes in ancient birds. “Yi qi really just shattered that idea.” (O'Connor also helped describe the first bird fossil found with an egg inside.)
Some researchers now think that flight arose at least four separate times within dinosaurs, including among scansoriopterygids. But healthy skepticism around Yi qi lingered. The animal has strange, rod-like bones called styliform elements that jut off its wrists, and paleontologists thought they might be there to help prop up a large wing membrane. But no other dinosaur, living or dead, also had such a bone—until Ambopteryx.
The newfound fossil not only has styliform elements, it also preserves a brownish film on one wing—a material that's thought to be traces of wing membrane. What's more, Ambopteryx has fossilized feathers and a pygostyle, a group of fused tail vertebrae that anchors the tail feathers in living birds.
A flying 'dinosaur squirrel'
A local farmer found the Ambopteryx fossil in 2017 outside a village near Lingyuan, a city in northeastern China's Liaoning Province. When the IVPP first acquired the fossil, researchers thought it might be an early bird, so Wang—an expert on the early evolution of birds—took the lead. But as preparators carefully removed excess rock, Wang realized that the animal wasn't a bird at all. (Find out more about birds, the dinosaurs that didn't die.)
Now fully exposed, the fossil preserves in detail how Ambopteryx made its living. In all likelihood, it was an opportunistic omnivore: Its stomach contains gizzard stones like those in today's plant-eating birds, but it also bears bone fragments, signs that the creature enjoyed a meaty snack soon before death. The adult animal weighed just a few hundred grams, give or take.
Researchers are still crunching the numbers on how well it could have flown—though at a minimum, it looks well-suited to gliding among trees. Its feet suggest that it evolved to perch on trees, but rather than acting like a songbird, the team thinks it may have behaved like today's flying squirrels and sugar gliders.
“It probably would have been climbing around in the trees—like a little, creepy-looking dinosaur squirrel—and then flying from branch to branch,” O'Connor says.
“If you were going to get a gliding arboreal theropod, it would be a really weird animal, and it would look pretty much like this,” says University of Southern California paleontologist Mike Habib, a biomechanics expert who is studying the flight of Yi qi.
Flying into the unknown
Scientists are keen to find more hints of soft tissue in Ambopteryx, which new imaging techniques could make easier. For instance, University of Hong Kong paleontologist Michael Pittman has used lasers to reveal soft-tissue traces in fossils of the feathered dinosaur Anchiornis.
And Pittman is no stranger to scansoriopterygids. At the 2018 meeting of the Society of Vertebrate Paleontology, Pittman's Ph.D. student Arindam Roy presented early results from the lab's laser scans of Yi qi. Wang and Pittman say they are talking to each other about doing a similar analysis of Ambopteryx.
To get clearer answers, paleontologists say the ideal would be to find an even better-preserved relative of Ambopteryx. That's a lot to ask for—but sites in China preserve feathered dinosaurs in mind-boggling detail. Perhaps an even more pristine bat-winged creature is waiting to be unearthed.
“We've gotten so used to great Chinese fossils, we start making really inappropriate asks, like, Well, why didn't you find one that's preserved perfectly in every detail and shows everything laid out?” Habib quips. “It's totally raised the bar of what a good fossil is.”