Illustration depicting a rendering of two Scleromochlus tayloris on a lush forest floor.

230-million-year-old mystery fossil sheds light on origins of pterosaurs

Discovered 115 years ago, the ancient creature posed a paleontological puzzle that new X-ray scans have solved.

In this life reconstruction, two Scleromochlus taylori circle each other in the sweltering environs of what is now Scotland some 231 million years ago. New research has identified Scleromochlus as a lagerpetid, a close cousin to the ancient flying reptiles known as pterosaurs.
Rendering by Gabriel Ugueto

Since 1907, paleontologists have been flummoxed by strange fossils that formed some 231 million years ago in the ancient sand dunes of what’s now Scotland. The fossils don’t preserve any bones: just the outlines of them etched into grainy sandstone. To study these imprints, scientists once had to pour wax or plastic onto the slabs and peel off molds—techniques that revealed an oddball. The peeled materials offered hints of an eight-inch-long reptile with what looked like long hindlimbs, a short neck, bizarrely short ribs, and an oversized head.

This creature, named Scleromochlus taylori, has bounced around the reptile family tree ever since its discovery, with generations of scientists trying to pin down its identity. Researchers also have struggled to reconstruct how it lived, such as whether the creature jumped through ancient sand dunes like today’s jerboas and other hopping rodents. Now, after more than a century, Scleromochlus has been unmasked thanks to new anatomical discoveries—which could help scientists understand the evolution of pterosaurs, the flying reptiles that lived alongside the dinosaurs.

High-resolution X-ray scans, published today in the journal Nature, reveal never-before-seen anatomical features that place Scleromochlus within a group of reptiles called the lagerpetids, which lived from roughly 240 million years ago to the end of the Triassic period about 201 million years ago. “Scleromochlus, at the time it was discovered, was just this weird and bizarre creature … so it was very difficult to understand,” says lead study author Davide Foffa, a paleontologist at Virginia Tech and the United Kingdom’s University of Birmingham who performed the research at the National Museums Scotland.

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