Science

160m-year-old dinosaurs struggled to fly despite bat-like wings, study finds

Yi qi and Ambopteryx longibrachium only managed to “glide clumsily between the trees”.

Two tiny dinosaurs species that lived about 160 million years ago struggled to fly despite having bat-like wings, scientists have found.

Yi qi and Ambopteryx longibrachium, who roamed the lands in China during the Late Jurassic period, only managed to “glide clumsily between the trees”.

The scientists believe these small dinosaurs, described in the journal iScience, became extinct in a very short period of time as they could not compete with other tree-dwelling dinosaurs and early birds.

Thomas Dececchi, assistant professor of biology at Mount Marty University in the US and first author on the study, 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.”

Both Yi and Ambopteryx were small animals, weighing less than two pounds.

Researchers say that they are unusual examples of theropod dinosaurs, the group that gave rise to birds.

a map of the skeleton and soft tissues of Yi qi
A map of the skeleton and soft tissues of Yi qi (Thomas Alexander Dececchi/iScience)

This is because while most theropods were ground-loving carnivores, Yi and Ambopteryx were comfortable in the trees and lived on a diet of insects, seeds and other plants.

Previous research has shown that both Yi and Ambopteryx had membranous wings and a styliform, a long and pointed forelimb.

Scientists have speculated that membranous wings and elongated forelimb point to a weak flying prowess.

To find out more, the researchers examined the fossils of both dinosaurs using a scanning technique known as laser-stimulated fluorescence (LSF).

They focused on the soft-tissue details in the fossils that cannot be seen in standard white light.

The team then used mathematical models to predict how these birds may have flown, taking into account their wingspan, weight and muscle placement.

Prof Dececchi said: “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.

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

But the researchers said gliding did help these dinosaurs stay out of danger at certain times.

Prof Dececchi said: “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.

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

According to Prof Dececchi and his team, the findings support the general consensus that dinosaurs evolved flight in several different ways before modern birds evolved.

They said both Yi and Ambopteryx show a “unique but failed flight architecture of non-avialan theropods” which may have contributed to their extinction.

Prof Dececchi said: “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.”

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