PARIS: A finger-sized fossil discovered in the United States 308 million years ago offers tantalizing clues to the habits of tiny dinosaur-like creatures that may have been precursors to reptiles, researchers revealed Wednesday.
The new species is a microsaur – tiny lizard-like animals that roamed the Earth well before the proper dinosaurs appeared.
The discovery sheds important light on the evolution of various animal groups, including amphibians and reptiles, the 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 details of that infection are not well known,” co-author Arjan Mann, a postdoctoral research fellow at the Smithsonian Institution, told AFP.
“Microsaurs have recently become important in understanding the origins of amniotes,” he said. “Many of these microsaurs are thought to be either the ancestors of amphibians or the ancestors of reptiles.”
Nestled in a swamp in today’s central United States, the specimen’s serpent-like body measures about 5 centimeters (2 in).
The animals had four short, thick legs.
In reference to its small size, researchers dubbed the new species Jörmungandr bolti, after a giant sea serpent from Norse mythology that fought with Thor.
The scientists were astonished to learn that the fossil also contained animal skin.
“The areas of skin were previously only known from fragmentary fossils,” Mann said.
“This microsaur is the complete shebang. … It’s so rare for these fossils to have a skin with anything 300 million years old!”
Contrary to previous ideas about microsaurs, which were classified as amphibians, Mann and his team found that Jörmungander had scales.
“Modern amphibians … are soft and slimy things, it was not a soft and slimy thing,” Mann said. “This animal actually had what a reptile looked like.”
Mann said the research suggests not only that microsaurs may have been early relatives of reptiles, but that burial ability may have played a bigger role in the origins of amniotes than was originally thought.
The researchers used a highly sensitive imaging technique called scanning electron microscopy (SEM) to take a closer look at the nearly complete fossil.
They discovered a pattern similar to the ridges found on the scales of modern reptiles that dig into the ground.
The size of the scale, along with other features such as a strong skull and elongated body, led researchers to speculate that Jormungandra also had burials.
“It probably would have been a head-first burrower, using its head to burrow itself into the mud,” Mann said.
“Its limbs probably weren’t doing much work. It may have used them to stabilize itself as it was moving around. But its primary mode of motion would have been winding like a snake.”
The SEM imaging technique is now being applied to many other ancient fossils, Mann said.
“We plan to scale 3D printing to a lot of SEMs and larger sizes,” he said. “And some biomechanics to see how they interacted with things like dirt and water.”