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Early pterosaur terrestrial locomotion abilities (free pdf)



Ben Creisler
bcreisler@gmail.com


A new open-access paper:


Mark P. Witton (2015)
Were early pterosaurs inept terrestrial locomotors?
PeerJ 3:e1018
doi: https://dx.doi.org/10.7717/peerj.1018
https://peerj.com/articles/1018/


Pterodactyloid pterosaurs are widely interpreted as terrestrially
competent, erect-limbed quadrupeds, but the terrestrial capabilities
of non-pterodactyloids are largely thought to have been poor. This is
commonly justified by the absence of a non-pterodactyloid footprint
record, suggestions that the expansive uropatagia common to early
pterosaurs would restrict hindlimb motion in walking or running, and
the presence of sprawling forelimbs in some species. Here, these
arguments are re-visited and mostly found problematic. Restriction of
limb mobility is not a problem faced by extant animals with extensive
fight membranes, including species which routinely utilise terrestrial
locomotion. The absence of non-pterodactyloid footprints is not
necessarily tied to functional or biomechanical constraints. As with
other fully terrestrial clades with poor ichnological records, biases
in behaviour, preservation, sampling and interpretation likely
contribute to the deficit of early pterosaur ichnites. Suggestions
that non-pterodactyloids have slender, mechanically weak limbs are
demonstrably countered by the proportionally long and robust limbs of
many Triassic and Jurassic species. Novel assessments of pterosaur
forelimb anatomies conflict with notions that all non-pterodactyloids
were obligated to sprawling forelimb postures. Sprawling forelimbs
seem appropriate for species with ventrally-restricted glenoid
articulations (seemingly occurring in rhamphorhynchines and
campylognathoidids). However, some early pterosaurs, such as
Dimorphodon macronyx and wukongopterids, have glenoid arthrologies
which are not ventrally restricted, and their distal humeri resemble
those of pterodactyloids. It seems fully erect forelimb stances were
possible in these pterosaurs, and may be probable given proposed
correlation between pterodactyloid-like distal humeral morphology and
forces incurred through erect forelimb postures. Further indications
of terrestrial habits include antungual sesamoids, which occur in the
manus and pes anatomy of many early pterosaur species, and only occur
elsewhere in terrestrial reptiles, possibly developing through
frequent interactions of large claws with firm substrates. It is
argued that characteristics possibly associated with terrestriality
are deeply nested within Pterosauria and not restricted to
Pterodactyloidea as previously thought, and that pterodactyloid-like
levels of terrestrial competency may have been possible in at least
some early pterosaurs.