A mysterious terrestrial reptile unearthed in a Scottish sandstone over 100 years ago turns out to be part of a famous flying family. Tiny Scleromochlus taylori was a close relative of pterosaursthe winged reptiles that lived alongside dinosaurs, researchers report online Oct. 5 in Nature.
This discovery supports the idea that pterosaurs – the first vertebrates to master powered flight – evolved from small, fast, two-legged ancestors.
The study also offers an answer to a long-standing mystery: what, exactly, was S.taylori? “It all comes down to preserving this animal,” says Davide Foffa, a paleontologist at the National Museums Scotland in Edinburgh.
S.taylori is fully known from seven individuals preserved in rocks discovered in 1907, fossils that are difficult to interpret. For one, there are no actual bones, just impressions of the surrounding rock; the bones have long vanished. Many studies have described and redescribed the creature from these fossils. And these analyzes in turn suggested that S.taylori was most closely related to dinosaurs, or pterosaurs, or even crocodilian ancestors.
What was clear was that the tiny reptile, which lived around 230 million years ago, had a very odd set of body proportions, Foffa says. Measuring less than 20 centimeters long, “it would fit in the palm of your hand”, but its head was very large for its body. It also had a short neck and long hind limbs. But this sketch is not enough to identify the creature’s closest relatives; which requires finer details of the skull, jaw, body proportions and more.
So Foffa and his colleagues used a noninvasive scanning technology called microcomputer tomography to collect previously inaccessible data on fossils, from the length of its tail to the size of its foot bones to the shape of its jaw. .
Some of the creature’s features – like its giant head – are similar to pterosaurs. Others, like the orientation of its lower jaw, don’t look like pterosaurs at all, the team found. S.taylori had no identifiable adaptations for flying, jumping or living in trees, the team said. Instead, it was probably a runner.
One of the most important new insights concerns the structure of the creature’s femur. It bore strong similarities to pterosaurs and a group of small land reptiles called lagerpetids. In particular, the bottom of the femur bone, where it would connect to the lower leg, bears a structure characteristic of lagerpetids, Foffa explains.
Taken together, the new data suggests the creature was almost certainly a lagerpetid. Although lagerpetids do not fly, they and pterosaurs have recently been recognized as being very closely related, part of a group collectively called pterosauromorphs. The common ancestor of pterosauromorphs was probably a small, fast reptile.
S.taylori, which has features of both, may be a very early lagerpetid, evolving soon after these two pterosauromorph lineages separated. That it turned out there were so many features present in both was “kind of a surprise,” says Martín Ezcurra, a paleontologist at the Argentine Museum of Natural Sciences in Buenos Aires, who was not involved in the news. study. But based on the reanalysis of the fossils, the conclusion that S.taylori was an early lagerpetid makes a lot of sense, he says.
Pterosaurs first appear in the fossil record around 220 million years ago, and their anatomy is distinct, including massive heads for their body sizes and the super elongated fourth digits that were part of their wings (SN: 10/12/10). S.taylori has a big head, but his hands are still small, notes Ezcurra. “We are missing several intermediate forms between the two that carry characteristics related to active flight,” he says. But this new analysis of ancient fossils brings scientists one step closer to when pterosaurs unique and highly flight-adapted bodies began to evolveSN: 07/22/21).
It’s hard to say what such a proto-pterosaur might look like, says Hans Sues, a paleontologist at the Smithsonian Institution in Washington, DC, who was not involved in the new study. “Scleromochlus is a small animal, and it is conceivable that a form related to the small body climbed the trees and eventually gave rise to a proto-pterosaur – perhaps through an intermediate gliding stage.