Wednesday, May 8, 2019

Speaking of Science: Did this dino soar?

Speaking of Science
Talk nerdy to us

A 3-D reconstruction of the small dinosaur Ambopteryx longibrachium. (Min Wang/Chinese Academy of Sciences)

Many tiny dinosaurs scampered through Jurassic forests, but a newly described critter, Ambopteryx longibrachium, may not have stuck to the ground. A fossil discovered in China reveals the dino had a flap of skin that ran the length of its long wrist and extended to slender finger bones — a membrane not unlike a bat's wing.

The big question, then, is: Could this hamster-size dinosaur not only scamper but fly? The authors of a study published Wednesday in Nature can't say for certain, but they embraced a gliding hypothesis. If they are correct, Ambopteryx represents an unusual experiment in soaring that took place 163 million years ago.

Several dinosaurs species, like the 150-million-year-old Archaeopteryx, sprouted wings and feathers. Archaeopteryx may have flown, though its exact relationship to modern birds, which descended from dinosaurs, is a matter of debate.

Far fewer dinosaur fossils show wing membranes. Ambopteryx and its close cousin, named Yi qi, are the only two dinosaur species with these features (and no birds descended from them). They were "likely able to glide," said Min Wang, an author of the study and a paleontologist at the Chinese Academy of Sciences in Beijing. They were probably worse fliers than today's birds and bats, he said, or yesterday's pterosaurs (flying reptiles that lived among, but were not themselves, dinosaurs).

"I would say they would look more like some flying squirrels," the rodents which do not actually fly but control their slow falls with parachutes of loose skin. These dinosaurs, like squirrels, probably lived in trees, and the membranes could have "evolved in the context of tree-climbing," Wang said.

The preservation of the Ambopteryx fossil is "astonishing," Wang said. Its stomach contains bones from a partially digested meal. Like Yi qi, Ambopteryx has a unique bone protruding from its forelimb, similar to but not exactly an extra finger. Wang and his colleagues call this a "styliform element," which would have been another attachment for membranous wings.

Kevin Padian, a paleontologist at the University of California at Berkeley who was not involved with this study, said the fossil was an important find. But, he cautioned, its strange body shape does not necessarily mean it could fly or glide. Ambopteryx may have used its membrane in a behavior known as "wing-assisted inclined running." Certain birds, like some partridges, can dash up vertical inclines with a boost from their wings. It's impressive, but it's not flight, any more than parkour is.

Padian said the skeleton, as described, cannot explained the range of motion or function of the strange front limbs. "I do not say they are wrong," he said, of the authors, but "we simply know too little."

A) The fossil; B) The restoration, with scale bar at 10 millimeters; C) Close-up of the membranous wing, labeled mw; D) Details of the bony stomach content. (Min Wang/Chinese Academy of Sciences)



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