Fossil reveals the burrowing lifestyle of a tiny dino

A finger-sized fossil discovered 308 million years ago in the United States gives tantalizing clues to the habits of tiny dinosaur-like creatures that could be the precursors of reptiles, researchers revealed Wednesday.

The new species are microsaurs, small, lizard-like animals that roamed the Earth long before the proper dinosaurs made their appearance.

The discovery sheds important light on the evolution of different groups of animals, including amphibians and reptiles, scientists wrote in the journal Royal Society Open Science.

Microsaurs lived during the Carboniferous Period, when the ancestors of modern mammals and reptiles, called amniotes, first appeared.

“Many of the details of this transition are not well known,” study co-author Arjan Mann, postdoctoral researcher at the Smithsonian Institution, told AFP.

“Microsaurs have recently become important in understanding the origins of amniotes,” he said. “Many of these microsaurs are believed to be ancestors of amphibians or ancestors of reptiles. “

Locked in a bog in what is now the central United States, the specimen’s snake-shaped body measures about five centimeters (two inches).

The animals had four short, plump legs.

Out of respect for its small size, researchers nicknamed the new species Joermungandr bolti after a giant sea serpent from Norse mythology that fought with Thor.

Scientists were amazed to discover that the fossil also contained the animal’s skin.

“The areas of the skin had only been known from fragmentary fossils before,” Mann said.

“This microsaur is the whole shebang … it’s very rare for these fossils. It’s very rare for a 300 million year old object to have skin with it!”

Headfirst Burrower

Contrary to previous ideas about microsaurs, which had been classified as amphibians, Mann and his team discovered that Joermungandr had scales.

“Modern amphibians … are soft slimy things, it wasn’t a soft slimy thing,” Mann explains.

“This animal really looked like a reptile.”

Mann said the research suggests not only that microsaurs may be the first parents of reptiles, but also that the ability to dig may have played a larger role in the origin of amniotes than originally thought. .

The researchers used a very sensitive imaging technique called scanning electron microscopy (SEM) to observe the near-perfect fossil up close.

They discovered a pattern of ridges similar to those found on the scales of modern reptiles that burrow into the ground.

Along with other features such as a sturdy skull and elongated body, the shape of the scale led researchers to speculate that Joermungandr had also buried himself.

“He probably would have been a head-first burrower, using his head to dig into the ground,” Mann said.

“His limbs probably weren’t very functional. He may have used them to stabilize himself as he wobbled. But his primary mode of movement would have been a sideways curl like a snake.”

The SEM imaging technique is now being applied to many other ancient fossils, Mann said.

“We plan to do a lot of SEM and also 3D print the scales at larger sizes,” he added. “And a little bit of biomechanics to see how they interact with things like dirt and water.”

© 2021 AFP