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Azhdarchid pterosaurs: water-trawling pelican mimics or "terrestrial stalkers"?

100%

Witton M. P., Naish D.

Acta Palaeontologica Polonica

2015

tom 60

nr 3

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: (i) azhdarchid fossils routinely occur in aquatic deposits; (ii) terrestrially-foraging pterosaurs were highly vulnerable to predation and (iii), 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.

Evolution of the pterosaur pelvis

80%

Hyder E. S., Witton M. P., Martill D. M.

Acta Palaeontologica Polonica

2014

tom 59

nr 1

Pterosaur pelvic girdles are complex structures that offer a wealth of phylogenetic and biomechanical information, but have been largely overlooked by pterosaur anatomists. Here, we review pterosaur pelvic morphology and find significant differences that correlate well with pterosaur clades identified in some phylogenetic analyses. We find that the length and orientation of the iliac processes, position of the acetabulum, extent of the ischiopubic plate and presence of supraneural fusion in adult individuals are taxonomically informative. Ontogenetic changes in pelvic morphology dictate that osteologically mature specimens are required to assess the development of many of these characteristics. We suggest that pelvic characters can readily be incorporated into pterosaur phylogenetic analyses and may assist in resolving the controversial interrelationships of this group. Distinctive pterosaur pelvic morphotypes suggest considerable differences in stance, locomotory kinematics and hindlimb functionality across the group.

Ograniczanie wyników

2 Acta Palaeontologica Polonica

2 Witton M. P.

1 Hyder E. S.

1 Martill D. M.

1 Naish D.

1 2015

1 2014

Wyniki wyszukiwania

Azhdarchid pterosaurs: water-trawling pelican mimics or "terrestrial stalkers"?

Evolution of the pterosaur pelvis