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Hand and foot morphology maps invasion of terrestrial environments by pterosaurs in the mid-Mesozoic

Hand and foot morphology maps invasion of terrestrial environments by pterosaurs in the mid-Mesozoic

NEWS - Pterosaurs, the first true flying vertebrates, played a significant role in Mesozoic terrestrial ecosystems from about 252–66 million years ago. However, our understanding of their ability to move on land more broadly and their terrestrial paleoecology is limited.

The researchers show a remarkably high degree of variation in pterosaur hands and feet, comparable to that observed in birds today, suggesting that pterosaurs adapted to a wide range of non-aerial locomotor ecologies throughout history.

Early small-bodied, long-tailed (non-pterodactyliform) pterosaurs exhibited extreme modifications in hand and foot proportions indicative of a climbing lifestyle. In contrast, the hands and feet of short-tailed (pterodactyliform) pterosaurs typically exhibit morphology consistent with a more terrestrial locomotor ecology.

"Early pterosaurs were highly specialised for climbing with modifications to their hands and feet, similar to today's climbing lizards and woodpeckers. Holding on to a vertical surface using the fingertips for long periods of time is a difficult task, much easier for small, light animals," says Robert Smyth of the University of Leicester.

This change in proportions correlates with other modifications to pterosaur anatomy, in particular, the separation along the midline of the flight membrane (cruropatagium) that connected the hind limbs and enabled much more effective locomotory abilities on the ground.

Together, these changes map out a key event in tetrapod evolution in the mid-Mesozoic colonisation of terrestrial environments by short-tailed pterosaurs.

"The hind limbs connected by a flight membrane would have constrained walking and running in early pterosaurs. In more advanced pterosaurs, this membrane separated along the midline allowing each hind limb to move independently," says David Unwin of the University of Leicester.

"This was a major innovation that, combined with changes to their hands and feet, greatly increased the mobility of pterosaurs on land. Freed from the constraints of climbing, these later pterosaurs could grow to enormous sizes, with some species becoming true giants in the Mesozoic," says Unwin.

This transition to a predominantly land-based locomotory ecology did not occur as a single event coinciding with the origin of short-tailed forms, but evolved independently in each of four major radiations: euctenochasmatians, ornithocheiroids, dsungaripteroids and azhdarchoids.

The invasion of terrestrial environments by pterosaurs facilitated the evolution of a wide range of new feeding ecologies, while freedom from the constraints imposed by climbing allowed the increase in body size that ultimately enabled the evolution of gigantism in a range of lineages.

"This finding underscores the need to study all aspects of pterosaurs, not just flight. Pterosaur flight is only one part of their story. By studying how they lived in trees and on the ground, we can begin to understand the role they played in ancient ecosystems," Smyth said.

Original research

Smyth, Robert S.H. et al. (2024). Hand and foot morphology maps invasion of terrestrial environments by pterosaurs in the mid-Mesozoic. Current Biology, DOI:10.1016/j.cub.2024.09.014

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