Pterosaurs, the flying reptiles that thrived during the age of dinosaurs, achieved great size – some with wingspans like a fighter jet – and displayed striking anatomy including exotic head crests and a hugely elongated finger to support their wings.
While the ancestry and early evolution of these creatures have long puzzled scientists, a fresh examination of remains found in Scotland of a small reptile that lived about 230 million years ago during the Triassic Period is helping shed light on the humble origins of pterosaurs, researchers said on Wednesday.
They found that the reptile, called Scleromochlus Taylor, is a close cousin of pterosaurs. It is a member of a group called lagerpetids, considered the nearest relatives of pterosaurs. Though not a direct ancestor, the researchers said Scleromochlus may look very much like the reptiles from which pterosaurs evolved.
Scleromochlus, which measured about 8 inches (20 cm) long and likely ate insects and other small invertebrates, featured a relatively large head, long and slender limbs, short torso and long tail, probably walking on two legs and standing on its toes. It did not have a lizard-like or frog-like sprawling posture as previously hypothesized.
“It would comfortably fit in a hand,” said Davide Foffa, a postdoctoral researcher in palaeontology at Virginia Tech and the University of Birmingham who worked on the research while at the National Museums Scotland in Edinburgh and is the lead author of the study published in the journal Nature. “Scleromochlus provides unique information about the ancestors of pterosaurs, showing that they likely derived from small-bodied land-dwelling runners.”
Scleromochlus lived at about the same time as the earliest dinosaurs, predating pterosaurs by perhaps 10 million years.
The researchers used sophisticated scanning technology to peer inside sandstone containing the Scleromochlus fossils, clearly revealing its anatomy for the first time. Fossils of seven Scleromochlus individuals were unearthed near the town of Elgin on Scotland’s northeastern coast and first described in 1907, but technology at the time did not permit a detailed understanding of the animal.
“Scleromochlus may not be a large fierce predator, but it reminds us of a very interesting story. It shows that very iconic animal such as pterosaurs – but this applies to dinosaurs and many other groups – likely began from unassuming-looking ancestors,” Foffa said.
Pterosaurs became Earth’s first flying vertebrates, with birds appearing about 150 million years ago and bats about 50 million years ago. The first pterosaurs were small – about crow-sized – but later ones had wingspans up to 35 feet (10.7 meters).
“They are really peculiar animals, with such a bizarre type of body that it’s hard to figure out what their closest relatives and ancestors are,” said University of Edinburgh palaeontologist and study co-author Steve Brusatte.
“Imagine a fuzzy creature that looks like a hang glider, with huge wings of skin attached to a long skinny finger like a giant sail, with a crocodile’s snout and tiny feet with toothpick toes and a long stiff tail, and that’s a pterosaur,” Brusatte added.
Unlike birds, pterosaurs did not use feathers for flight, though their bodies were covered in fuzzy little feathers. Their wings were formed by a tough membrane extending from an elongated fourth finger to the ankle.
Fossils of lagerpetids are known from Africa, North America and South America, with Scleromochlus the only one found in Europe.
“Scleromochlus still looks quite different from pterosaurs. It’s kind of like a monkey compared to a human,” Brusatte said. “Clearly it’s a primitive cousin, as it shares features of its delicate bones, especially its small pelvis and the in-turned thigh bone that connects to it. But Scleromochlus did not yet have a wing. It was not yet a flier. Evolution still had a lot of work to do.”