Artist's impression of a sliding Ambopteryx longibrachium
The first dinosaurs to blow up were a failed evolutionary experiment. They had wings made from a skin membrane, similar to bats, but they could not fly well and were soon outpaced by birds.
"They were poorly designed gliders," says Alex Dececchi of Mount Marty University in South Dakota. "You were squeezed out."
Birds evolved from dinosaurs, and it was previously believed that they were the only evolutionary branch that gained the ability to fly. In 2015, Xing Xu of the Institute of Vertebrate Paleontology in Beijing reported the discovery of a bizarre fossil called Yi Qi, which means “strange wing” in Mandarin Chinese, with wings made from a bat-like membrane instead of feathers.
In 2019, a team from Xu uncovered a fossil of another species of membrane wing called Ambopteryx longibrachium.
Now a team that includes Dececchi and Xu has conducted a more detailed study of these animals' flight abilities, based in part on laser scans of the Yi fossil, which has revealed more details about their soft tissues. However, it is still not clear what shape the wings were, so the team looked at different arrangements.
One possibility is that these animals had wings that were shaped like bats and connected to their legs. Another is that they were shaped more like birds. It was most likely something in between, thinks the team.
The results suggest that Yi and Ambopteryx were not only incapable of powered flight, as previously thought, but could also not glide as well as some modern animals such as flying squirrels. This means they were almost certainly tree-dwelling animals that only glide short distances, the team believes.
By the time the Yi and Ambopteryx evolved about 160 million years ago, there were no birds and the sky was dominated by relatively large pterosaurs, a group separate from dinosaurs. But when birds evolved a few million years later, membrane-winged dinosaurs had nowhere evolutionarily to go.
They couldn't compete with birds of similar size because birds were better fliers, Dececchi says. And they couldn't get any bigger because they couldn't compete with pterosaurs either. "These guys never stood a chance," he says.
Of course, much later, about 50 million years ago, bats managed to develop into highly qualified airmen. This could have been possible because bats were nocturnal and therefore did not compete directly with birds.
"Being at night could have given them a window," says Dececchi. In contrast, there is no reason to believe that Yi and Ambopteryx were active at night.
Journal reference: iScience, DOI: 10.1016 / j.isci.2020.101574
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