These two bird-sized dinosaurs evolved the ability to glide, but weren't
great at it

Date:
October 22, 2020
Source:
Cell Press
Summary:
Despite having bat-like wings, two small dinosaurs, Yi and
Ambopteryx, struggled to fly, only managing to glide clumsily
between the trees where they lived, researchers report. Unable
to compete with other tree- dwelling dinosaurs and early birds,
they went extinct after just a few million years. The findings
support that dinosaurs evolved flight in several different ways
before modern birds evolved.



FULL STORY ========================================================================== Despite having bat-like wings, two small dinosaurs, Yi and Ambopteryx, struggled to fly, only managing to glide clumsily between the trees where
they lived, researchers report October 22 in the journal iScience. Unable
to compete with other tree-dwelling dinosaurs and early birds, they
went extinct after just a few million years. The findings support that dinosaurs evolved flight in several different ways before modern birds
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 first
author Thomas Dececchi, Assistant Professor 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." Yi and Ambopteryx were small animals from Late Jurassic
China, living about 160 million years ago. Weighing in at less than two
pounds, they are unusual examples of theropod dinosaurs, the group that
gave rise to birds. Most theropods were ground-loving carnivores, but Yi
and Ambopteryx were at home in the trees and lived on a diet of insects,
seeds, and other plants.

Curious about how these animals fly, Dececchi and his collaborators
scanned fossils using laser-stimulated fluorescence (LSF), a technique
that uses laser light to pick up soft-tissue details that can't be seen
with standard white light. Later, the team used mathematical models to
predict how they 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. 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,"
says Dececchi. "They could glide, but even their gliding wasn't great."
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
and Ambopteryx 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. It's not a great thing to do, but sometimes it's a choice between losing a bit of energy and being eaten,"
says Dececchi. "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 researchers are now
looking at the muscles that powered Yi and Ambopteryx 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," Dececchi says. "To work where we're just trying to figure
out the possibilities for a weird creature is kind of fun." The authors
were supported by Mount Marty University and The University of Hong Kong.


========================================================================== Story Source: Materials provided by Cell_Press. Note: Content may be
edited for style and length.


========================================================================== Journal Reference:
1. Dececchi et al. Aerodynamics show membranous-winged theropods were
a poor
gliding dead-end. iScience, 2020 DOI: 10.1016/j.isci.2020.101574 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201022112613.htm

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