Have wings will glide – at best

Just having wings doesn’t mean you can fly. Yi qi and Ambopteryx longibrachium, it seems, were barely able to glide. And that contributed to their downfall.

The two small scansoriopterygid dinosaurs from Late Jurassic China, about 160 million years ago, were unique in developing wings of stretched skin, much like a bat’s. Anatomical analysis suggests, however, that they weren’t much good for anything other than moving clumsily between trees.

Perhaps not surprisingly, the pair went extinct after just a few million years and are really just a footnote in the story of how flight evolved.

“Once birds got into the air, these two species were so poorly capable of being in the air that they just got squeezed out,” says Thomas Dececchi from Mount Marty University, US, first author of a paper in the journal iScience.

“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.”

Scansoriopterygids were a branch of theropods, the group that gave rise to birds (and included no less than T. Rex). However, unlike most theropods, which were ground-loving carnivores, Yi and Ambopteryx were at home in the trees and ate insects, seeds and plants.

The discovery of their membranous wings caused quite a bit of interest, but it has not been clear what they were actually good for.

To find out, Dececchi and colleagues from the US, Hong Kong, China and Canada scanned fossils using laser-stimulated fluorescence, which can pick up soft-tissue details that can’t be seen with standard white light. They then used mathematical models to predict how they might have flown, testing variables such as 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,” Dececchi says.

“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.”

The findings add weight to the idea that dinosaurs evolved flight in several different ways before modern birds evolved, the researchers say.

They are now looking at the muscles that powered Yi and Ambopteryx to build a more comprehensive picture.