The team was surprised by a level of variation in the bones that is similar to what we see in living birds. The variation indicates that pterosaurs were more than just great fliers. Pterosaur species were well-adapted to live in a wide range of terrestrial habitats, including up in the trees and closer to the ground.

“Early pterosaurs were highly specialized for climbing, with extreme modifications in their hands and feet, similar to those found in climbing lizards and birds like woodpeckers today,” study co-author and University of Leicester paleontologist Robert Smyth said in a statement. “Clinging to vertical surfaces by your fingertips for long periods is hard work–it’s a lot easier for small, lightweight animals.”

These early pterosaur species were likely restricted to arboreal habitats, which made them physically smaller. However, a major evolutionary shift was in store during the Middle Jurassic period. Pterosaur hands and feet began to look much more like those of ground-dwelling animals. These adaptations for ground-based movements like walking opened the pterosaurs up to new ecological opportunities and more feeding strategies. Now that they were free from the size constraints of living in trees, some pterosaur species went on to evolve their gigantic wingspans.

“In early pterosaurs the hind limbs were connected by a flight membrane which severely impeded walking and running. In later, more advanced pterosaurs, this membrane became separated along the midline, allowing each hind limb to move independently,” study co-author and University of Leicester paleobiologist David Unwin said in a statement. “This was a key innovation that, combined with changes to their hands and feet, greatly improved pterosaurs’ mobility on the ground.

According to the team, the details of the hands and feet are a clear giveaway. Early pterosaurs had bones at the base of the fingers and toes were relatively short. The bones farther from the body were much longer and ended in large, curved claws. Both of these modifications together gave them a powerful grip that was ideal for climbing.

The later and more advanced pterosaurs had the opposite patterns. The bones positioned at the base of their fingers and toes were much longer, while the ones closer to the tips were shorter. They also had flatter and less curved claws, which suggested that these species were better adapted for walking rather than climbing.

By the time pterosaurs moved from trees to the ground, it was already inhabited by lots of other animals, including dinosaurs and numerous other reptiles. To avoid competition with these more established species, pterosaurs exploited ecological niches that required both flying and walking abilities. The result was some bizarre feeding strategies. Some pterosaurs had hundreds of fine, needle-like teeth for filter-feeding, the same way that modern day flamingos do.

“These findings underscore the need to examine all aspects of pterosaur locomotion, not just flight, to fully understand their evolution,” said Smyth. “That pterosaurs could fly is only one part of their story. By exploring how they lived in the trees or on the ground, we can begin to understand the roles that they played in ancient ecosystems.”