Membrane-Winged Dinosaurs Yi and Ambopteryx were Poor Gliders

Saturday, October 24, 2020

Ambopteryx longibrachium. Image credit: Chung-Tat Cheung & Min Wang / Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences.

Yi qi and Ambopteryx longibrachium are two bizarre scansoriopterygid theropods that lived in what is now China about 160 million years ago (Late Jurassic epoch). They had skin stretched between elongate fingers that form a potential membranous wing. Most theropods were ground-loving carnivores, but Yi qi and Ambopteryx longibrachium were at home in the trees and lived on a diet of insects, seeds, and other plants. According to a new study published in the journal iScienceYi qi and Ambopteryx longibrachium struggled to fly, only managing to glide clumsily between the trees where they lived; unable to compete with other tree-dwelling dinosaurs and early birds, they went extinct after just a few million years.

“Once birds got into the air, these two species were so poorly capable of being in the air that they just got squeezed out,” said first author Dr. Thomas Dececchi, a researcher in the Department of Biology at Mount Marty University.

“Maybe you can survive a few million years underperforming, but you have predators from the top, competition from the bottom, and even some small mammals adding into that, squeezing them out until they disappeared.”

Curious about how Yi qi and Ambopteryx longibrachium fly, Dr. Dececchi and colleagues scanned fossils using laser-stimulated fluorescence, a technique that uses laser light to pick up soft-tissue details that can’t be seen with standard white light.

They then used mathematical models to predict how these dinosaurs might have flown, testing many different variables like weight, wingspan, and muscle placement.

“They really can’t do powered flight. You have to give them extremely generous assumptions in how they can flap their wings,” Dr. Dececchi said.

‘You basically have to model them as the biggest bat, make them the lightest weight, make them flap as fast as a really fast bird, and give them muscles higher than they were likely to have had to cross that threshold.”

“They could glide, but even their gliding wasn’t great,” he noted.

Artist’s concept of Yi qi. Image credit: Dinostar.

While gliding is not an efficient form of flight, since it can only be done if the animal has already climbed to a high point, it did help Yi qi and Ambopteryx longibrachium stay out of danger while they were still alive.

“If an animal needs to travel long distances for whatever reason, gliding costs a bit more energy at the start, but it’s faster. It can also be used as an escape hatch,” Dr. Dececchi said.

“It’s not a great thing to do, but sometimes it’s a choice between losing a bit of energy and being eaten.”

“Once they were put under pressure, they just lost their space. They couldn’t win on the ground. They couldn’t win in the air. They were done.”

The authors are now looking at the muscles that powered Yi qi and Ambopteryx longibrachium to construct an accurate image of these bizarre little creatures.

“I’m used to working with the earliest birds, and we sort of have an idea of what they looked like already,” Dr. Dececchi said.

“To work where we’re just trying to figure out the possibilities for a weird creature is kind of fun.”


T. Alexander Dececchi et al. Aerodynamics Show Membrane-Winged Theropods Were a Poor Gliding Dead-end. iScience, published online October 22, 2020; doi: 10.1016/j.isci.2020.101574