Species New to Science's Journal

[Paleontology • 2024] Hand and Foot Morphology Maps Invasion of Terrestrial Environments by Pterosaurs in the mid-Mesozoic

Scaphognathus crassirostris (Goldfuss, 1831)

in Smyth, Breithaupt, Butler, Falkingham et Unwin, 2024.

DOI: 10.1016/j.cub.2024.09.014

Paleoart by Rudolf Hima.

Highlights

• The hands and feet of pterosaurs were adapted to a broad range of locomotor ecologies

• Early pterosaurs had a scansorial mode of life, which restricted maximum body size

• Anatomical changes in later pterosaurs led to more effective terrestrial ability

• Invasion of terrestrial habitats facilitated diverse feeding ecologies and gigantism

Summary

Pterosaurs, the first true flying vertebrates, played a crucial role in Mesozoic terrestrial ecosystems. However, our understanding of their ability to move around on the ground and, more broadly, their terrestrial paleoecology remains limited. Here, we demonstrate an unexpectedly high degree of variation in the hands and feet of pterosaurs, comparable with that observed in extant birds. This suggests that pterosaurs were adapted to a remarkably broad range of non-aerial locomotor ecologies. Small, early, long-tailed pterosaurs (non-pterodactyliforms) exhibit extreme modifications in their hand and foot proportions indicative of climbing lifestyles. By contrast, the hands and feet of later, short-tailed pterosaurs (pterodactyliforms) typically exhibit morphologies consistent with more ground-based locomotor ecologies. These changes in proportions correlate with other modifications to pterosaur anatomy, critically, the separation along the midline of the flight membrane (cruropatagium) that linked the hindlimbs, enabling a much more effective locomotory ability on the ground. Together, these changes map a significant event in tetrapod evolution: a mid-Mesozoic colonization of terrestrial environments by short-tailed pterosaurs. This transition to predominantly ground-based locomotor ecologies did not occur as a single event coinciding with the origin of short-tailed forms but evolved independently within each of the four principal radiations: euctenochasmatians, ornithocheiroids, dsungaripteroids, and azhdarchoids. Invasion of terrestrial environments by pterosaurs facilitated the evolution of a wide range of novel feeding ecologies, while the freedom from limitations imposed by climbing permitted an increase in body size, ultimately enabling the evolution of gigantism in multiple lineages.

Keywords: Mesozoic, Pterosauria, adaptive radiation, manus, pes, ecomorphology, locomotor ecology, arboreal, scansorial, terrestrial

Paleoart reconstruction of the non-pterodactyliform Scaphognathus crassirostris (Upper Jurassic) in scansorial mode

Paleoart by Rudolf Hima.

Paleoart reconstruction of the pterodactyliform Balaenognathus maeuseri (Upper Jurassic) in terrestrial mode

Paleoart by Rudolf Hima.

Comparison of autopodial and other anatomical differences between non-pterodactyliform (scaphognathine) and pterodactyliform pterosaurs (derived ctenochasmatoid)
(A) Paleoart reconstruction of the non-pterodactyliform Scaphognathus crassirostris (Upper Jurassic) in scansorial mode, with autopodia characterized by short proximal elements and elongated distal elements.
(B) Paleoart reconstruction of the pterodactyliform Balaenognathus maeuseri (Upper Jurassic) in terrestrial mode, with autopodia characterized by elongated proximal elements and shortened distal elements.
(C) Reconstructions of Scaphognathus (left) and Balaenognathus (right) in dorsal view indicating the principal flight surfaces.
(D) Simplified pterosaur phylogeny indicating the principal taxonomic groups used in this study.

Abbreviations: bp, brachiopatagium; cp, cruropatagium; pp, propatagium.

Paleoart by Rudolf Hima.

Robert S.H. Smyth, Brent H. Breithaupt, Richard J. Butler, Peter L. Falkingham and David M. Unwin. 2024. Hand and Foot Morphology Maps Invasion of Terrestrial Environments by Pterosaurs in the mid-Mesozoic. Current Biology. DOI: doi.org/10.1016/j.cub.2024.09.014