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Azhdarchid pterosaur feeding habits



From: Ben Creisler
bcreisler@gmail.com

A new online paper:

Mark P. Witton and Darren Naish (2013)
Azhdarchid pterosaurs: water-trawling pelican mimics or "terrestrial stalkers"?
Acta Palaeontologica Polonica (in press)
available online 28 Oct 2013
doi:http://dx.doi.org/10.4202/app.00005.2013
http://app.pan.pl/article/item/app000052013.html


The lifestyles of all pterosaurs are contentious, but those of the
pterodactyloid clade Azhdarchidae are particularly debated. A 2008
review of the functional morphology of azhdarchid pterosaurs concluded
that they were probably terrestrial foragers, as evidenced by their
long limbs, generalised skull construction, the arthrological
limitations of their cervical series, trackway data indicating
terrestrial proficiency, a strong continental skew in the depositional
context of their fossils, and several additional lines of
corroborating evidence. This hypothesis was recently challenged on
three counts: 1) azhdarchid fossils routinely occur in aquatic
deposits; 2) terrestrially-foraging pterosaurs were highly vulnerable
to predation and 3), aerial ‘water trawling’, where the mandible is
pulled though water to catch food in a distended throat pouch, is a
more likely foraging strategy. Pelican-like jaw mechanics were
suggested for azhdarchids because of the asymmetrical jaw joints in
these pterosaurs, which permit lateral deflection of the mandibular
rami during jaw extension. We evaluate these three claims and conclude
that all are flawed. The frequent occurrence of azhdarchid fossils in
aquatic sedimentary systems is not significant with regard to ecology
or behaviour, since these provide the overwhelming mechanism for the
preservation of all fossil terrestrial animals. Likely pterosaur
takeoff abilities and the ubiquitous nature of modern,
terrestrially-foraging birds indicate that predation risks on
ground-foraging pterosaurs are probably overstated. The kinematics of
pterosaur jaws are entirely different to those of pelicans, which are
highly specialised compared to those of all other tetrapods, and there
are no indications from azhdarchid jaw anatomy that azhdarchids
indulged in pelican-like foraging behaviour. The estimated amount of
jaw expansion present in azhdarchids was minimal compared to that of
pelicans, even when the asymmetrical jaw joints of azhdarchids are
taken into account. Moreover, the widespread occurrence of
asymmetrical jaw joints in other reptiles demonstrates that they are
not related to any specific feeding habits. We conclude that
terrestrial foraging remains the most parsimonious habit for
azhdarchid pterosaurs.