A reappraisal of azhdarchid pterosaur functional morphology and paleoecology - PubMed (original) (raw)

A reappraisal of azhdarchid pterosaur functional morphology and paleoecology

Mark P Witton et al. PLoS One. 2008.

Abstract

Azhdarchid pterosaurs were among the most widespread and successful of pterosaur clades, but their paleoecology remains controversial. Morphological features common to all azhdarchids include a long, shallow rostrum; elongate, cylindrical cervical vertebrae that formed a long and unusually inflexible neck; and proportionally short wings with an abbreviated fourth phalanx. While azhdarchids have been imagined as vulture-like scavengers, sediment probers, swimmers, waders, aerial predators, or stork-like generalists, most recent authors have regarded them as skim-feeders, trawling their lower jaws through water during flight and seizing aquatic prey from the water's surface. Although apparently widely accepted, the skim-feeding model lacks critical support from anatomy and functional morphology. Azhdarchids lack the many cranial specialisations exhibited by extant skim-feeding birds, most notably the laterally compressed lower jaw and shock absorbing apparatus required for this feeding style. Well-preserved azhdarchid skulls are rare, but their rostra and lower jaws appear to have been sub-triangular in cross-section, and thus dissimilar to those of skim-feeders and sediment probers. Taphonomic data indicates that azhdarchids predominately inhabited inland settings, and azhdarchid morphology indicates that they were poorly suited for all proposed lifestyles bar wading and terrestrial foraging. However, azhdarchid footprints show that their feet were relatively small, padded and slender, and thus not well suited for wading. We argue that azhdarchids were stork- or ground hornbill-like generalists, foraging in diverse environments for small animals and carrion. Proficient terrestrial abilities and a relatively inflexible neck are in agreement with this interpretation.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1

Figure 1. Reconstructed skeleton of Zhejiangopterus linhaiensis based on and .

Scale bar represents 500 mm.

Figure 2

Figure 2. The terrestrial skew of azhdarchid fossils based on data in

Table 1.

Figure 3

Figure 3. Azhdarchid skull material.

A, occipital region of Hatzegopteryx (modified from [7]), B, reconstruction of Quetzalcoatlus sp. based on photographs in ; C, Zhejiangoperus (modified from [40]); D, mandible of Bakonydraco (modified from [6]); Scale bars represent 100 mm.

Figure 4

Figure 4. Azhdarchid cervical vertebrae.

A–C, Quetzalcoatlus cervical vertebrae 3–5; D, Phosphatodraco cervical series in situ (after [47]). Scale bars represent 100 mm.

Figure 5

Figure 5. Azhdarchid wing shape.

A, reconstructed planform of Quetzalcoatlus (wing shape derived from the ‘dark wing’ Rhamphorhynchus: see [91]); B, planform of the dynamically soaring wandering albatross (Diomedea exulans); C, planform of the statically soaring Andean condor (Vultur gryphus). Images not to scale.

Figure 6

Figure 6. The probable azhdarchid trace fossil Haenamichnus uhangriensis.

A, the 7.3 m trackway CNUPH.P9; B, H. uhangriensis holotype (CNUPH.P2), manus (top) and pes (bottom) prints. Modified from . Scale bars represent 1 m (A) and 100 mm (B).

Figure 7

Figure 7. Suggested modern analogues of azhdarchids.

A, anterior premaxilla of the western sandpiper (Calidris mauri) showing densely packed Herbst corpuscles, dorsal view [after 110]; B, skull of the probing common snipe (Gallinago gallinago); C, skull of the black skimmer (Rynchops nigra) ; D, skull of the northern ground hornbill (Bucorvus abyssinicus). Scale bars represent 1 mm (A) and 10 mm (B–D).

Figure 8

Figure 8. Reconstructed feeding posture of an azhdarchid with sagittally aligned limbs, as evidenced by .

The blue line indicates the dorsal and cervical column; note how the long jaws require little flexion of the forelimb to be lowered to the ground and how only moderate flexion of the anterior cervical series would lower the jaws fully. Letters denote approximate angles used in this reconstruction; a, 30°; b, 80°; c, 120°; d; 35°; e, 145°.

Figure 9

Figure 9. Life restoration of a group of giant azhdarchids, Quetzalcoatlus northropi, foraging on a Cretaceous fern prairie.

A juvenile titanosaur has been procured by one pterosaur, while the others stalk through the scrub in search of small vertebrates and other foodstuffs.

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