Around 160 million years ago two small dinosaurs, named Yi and Ambopteryx, appeared in China. They clearly engaged in some sort of aerial activity, possessing bat-like wings. However, paleontologists now argue neither achieved true flight, instead they likely glided badly, leading them to be out-competed by birds.

When Yi was first discovered, the scientists that described it called it: “A pioneer in the evolution of flight on the line to birds.” Instead, Dr Thomas Dececchi of Mount Marty University thinks it was an evolutionary dead end, with birds evolving flight entirely independently.

Based on their wing structure and skull Dececchi, who is first author of the new study in iScience, concludes the two types of theropod dinosaurs lived in trees and probably fed on a mix of insects, seeds, and other plants. Like flying squirrels, sugar gliders, and even some snakes they presumably worked out it was quicker and safer to get from one tree to another by gliding than coming to the ground. Gradual adaptions extended the range they could travel.

However, when the team reconstructed the weight and muscle size of both Yi and Ambopteryx they concluded they were quite limited. "They really can't do powered flight. You have to give them extremely generous assumptions in how they can flap their wings. 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," Dececchi explained in a statement.

Neither of them could have got close to being able to take off from the ground – at best leaping from heights and using some flapping to extend their gliding distance. Basically, not flying (or gliding) but falling with style. 

Unafraid to dunk on creatures the size of pigeons that have been dead for 160 million years, Dececchi added, “They could glide, but even their gliding wasn't great.”

The authors conclude these small dinosaurs' fate was sealed once birds evolved and decided their distant relatives tasted good. “They couldn't win on the ground. They couldn't win in the air. They were done,” Dececchi said. 

"Once birds got into the air, these two species were so poorly capable of being in the air that they just got squeezed out. 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."

The team is now trying to unravel more details about Yi and Ambopteryx's wing structure and the muscles that support it, noting this is a much harder job than for the ancestors of birds, since we have no living descendents to guide us.

Lest you feel superior to these unsuccessful fliers, remember they survived for several millions of years, avoiding being eaten by terrifying pterosaurs, which had developed true flight. Humans, on the other hand, have been around for about 2 million years, and our species just 300,000, and probably shouldn't count on making it much longer.