Earlier this year, Dr. Michael Pittman of the University of Hong Kong reported that powered flight evolved at least three separate times: twice in feathered dinosaurs and once in early birds. The research also revealed that many ancestors of birds came close to having the wing loading and specific lift thresholds that are indicative of the potential for powered flight.
In collaboration with Dr. Thomas Dececchi, Dr. Pittman has expanded his flight origins investigation to include Scansoriopterygids, an unusual group of theropods that used bat-like wings for gliding.
The rare dinosaurs lived around 160 million years ago in what is now northern China. It is believed that Scansoriopterygids weighed about one kilogram and ate insects, seeds, and other plants.
Testing the theory of gliding ability among Scansoriopterygids is important for understanding how flight evolved among theropod dinosaurs. If confirmed, this bat-winged lifestyle would have been unique to Scansoriopterygids, and would also make them the most distantly related dinosaurs to birds that glide.
The team used mathematical models to predict how Scansoriopterygids may have flown, while accounting for many different variables such as weight, wingspan, and muscle placement. The experts found that Scansoriopterygids did not have powered flight potential but were capable of clumsy gliding.
“They could glide, but they weren’t very good at it. If I were them I would have been particularly worried about predators!” said Dr. Pittman. Their poor gliding abilities may have contributed to the brief existence of Scansoriopterygids.
“The two Scansoriopterygid species we studied were so poorly capable of being in the air that they just got squeezed out,” said Dr. Thomas Dececchi. “Maybe you can survive a few million years underperforming, but with birds, pterosaurs, gliding mammals all around, Scansoriopterygids were simply squeezed out until they disappeared.”
Since gliding is only a strategy that can be used from certain heights, it is not an efficient form of flight. However, it did help to keep Scansoriopterygids out of danger.
“If an animal needs to travel long distances, gliding costs a bit more energy at the start, but it’s faster. It can also be used as an escape hatch. It’s not a great thing to do, but sometimes it’s a choice between losing a bit of energy and being eaten,” said Dr. Dececchi.
“Once Scansoriopterygids 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 findings provide new evidence to support the idea that dinosaurs evolved flight in several different ways before modern birds emerged.
“Our team continues to uncover a greater sense of the breadth of experimentation involved in getting dinosaurs into the air,” said Dr. Pittman. “We plan to reveal even more details moving forward, particularly the different routes taken by dinosaurs to occupy the skies.”
The study is published in the journal iScience.