How Pterosaurs may have evolved from tiny, fast-running reptiles

A mysterious ground-dwelling reptile unearthed in a Scottish sandstone over 100 years ago turns out to be part of a famous flying family. Tiny Taylor was a close relative of pterosaurs, the winged reptiles that lived alongside the dinosaurs, researchers report online October 5 in Nature.
The finding lends support to the idea that pterosaurs — the first vertebrates to master powered flight — evolved from small, two-legged, speedy ancestors. The study also offers an answer to a long-standing mystery: What, exactly, was S. Taylor? “It all boils down to the preservation of this animal,” says Davide, a paleontologist at National Museums, Scotland in Edinburgh. S. Taylor is known entirely from seven individuals preserved in rocks discovered in 1907, fossils that have been difficult to interpret. For one thing, there aren’t any actual bones, just impressions on the surrounding rock; the bones have long since winnowed away. Numerous studies have described and re described the creature based on these fossils. And those analyses have in turn suggested that S. Taylor was most closely related to dinosaurs, or to pterosaurs, or even to crocodile ancestors. What was clear was that the little reptile, which lived about 230 million years ago, had a set of very odd body proportions, he says. At less than 20 centimeters long, “it would fit on 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 that rough outline isn’t enough to identify the creature’s closest relatives; that requires finer details of skull, jaw, body proportions and more.
So He and his colleagues used a noninvasive scanning technology called microcomputer tomography to collect previously inaccessible data from the fossils, from the length of its tail to the size of its foot bones to the shape of its jawline. Some of the creature’s features — like its giant head — are similar to pterosaurs. Others, like the orientation of its lower jaw, aren’t much like pterosaurs at all, the team found. S. Taylor didn’t have any identifiable adaptations for flying, jumping or living in trees, the team says. Instead, it was probably a runner. One of the most important new insights is about the structure of the creature’s femur. It bore strong similarities to both pterosaurs and, a group of small, ground-dwelling reptiles. In particular, the bottom of the femur bone, where it would connect to the lower leg, bears a structure that is a hallmark of them, said by him. It’s difficult to say what such a dinosaur might look like, says Hans Sues, a paleontologist at the Smithsonian Institution in Washington, D.C., who was not involved in the new study. “A tiny animal, and it is conceivable that a related small-bodied form climbed around in trees and eventually gave rise to a dinosaur — perhaps through an intermediate gliding stage.”  A new microcomputer tomography analysis of seven Scleromochlus Taylor fossil individuals allowed researchers to create this 3-D reconstruction of its skeleton, revealing new clues to the mysterious creature’s place on the tree of life. The creature shared some anatomical features with pterosaurs, but is most likely them, a group of ground-dwelling reptiles known to be closely related to pterosaurs.