Azhdarcho returns

Nesov started it all
A new paper on Azhdarcho neck vertebrae (Averianov 2013) promises to reopen the discussion on azhdarchid lifestyles. I did not know the Azhdarcho cervical series was so well known! Averianov argues (see abstract below) for a soaring, pelican-like lifestyle (promoted by Nesov 1984 = dipping for surface-dwelling sea life while on the wing) and against a more terrestrial stork-like one (promoted by Witton and Naish 2008).

The cervicals of Azhdarcho from Averianov 2013 demonstrating maximum flexion and extension. Red arrow points to the notarium. IMHO, there would be one intervening regular vertebra, #10.

Figure 1. The cervicals of Azhdarcho from Averianov 2013 demonstrating maximum flexion and extension. Red arrow points to the notarium. IMHO, there would be one intervening regular vertebra, #10. The relative size of the cervicals may be important. 7 and 8 are short and subequal in Zhejiangopterus, but #5 is not the longest by far, as it is in Azhdarcho. On the other hand, Quetzalcoatlus has a shorter #5 and #8. Not sure from this photo, but articular surfaces (zygopophyses) seem to be missing from #7 and #8. Surprising not to see more flexion here between all of the cervicals shown. Perhaps Averianov was being overly conservative.

From the abstract (truncated):
A computer reconstruction of isolated cervical vertebrae of Azhdarcho lancicollis from the Turonian of Uzbekistan allows three-dimensional model of the cervical region of the vertebral column of this animal. In a neutral posture, the neck of azhdarchids was not straight, as often reconstructed, but S-shaped, with the maximum angles between the V–VI (20°), VI–VII (20°), and VIII–IX (17°) vertebrae. The feeding strategy of azhdarchids was probably similar to that of pelicans. In a search for prey, azhdarchids were soaring above the water surface of large inland or nearshore marine water bodies. Their prey (predominantly fish) was captured by the widely open mouth and fell into the throat sac, the presence of which is suggested by the spiral jaw joint. Prey was swallowed during the abrupt neck flexion in the posterior segment, which brought the head in an almost horizontal position. A storklike wading ecology for azhdarchids is less probable, because these clumsy on land animals were vulnerable to terrestrial predators.

Click to enlarge. Averinov re-published images of Zhejiangopterus and Quetzalcoatlus from Witton 2007 and Wittion & Naish 2008 that demonstrate a certain devil-may-care attitude toward the anatomy, especially in Quetzalcoatlus. There was little regard for the the shape of the pelvis in both images and little regard for the lengths of the cervical elements and robust pectoral girdle in Q. My images, on the other hand, were traced from photos taken during a visit to Texas several years ago.

Figure 2. Click to enlarge. Averianov re-published images of Zhejiangopterus and Quetzalcoatlus from Witton 2007 and Wittion & Naish 2008 that appear to demonstrate a certain devil-may-care attitude toward the anatomy, especially in Quetzalcoatlus. There was little regard for the the shape and size of the pelvis in both images. In Q there was little regard for the shape of the skull, the lengths of the cervical elements, the size of the torso and the robust pectoral girdle and humerus (based on Q sp., which is much more gracile than the Q. northropi humerus). The extreme curvature of the femur was missed. So was the relative lengths of the metacarpus and tibia. My images, on the other hand, were traced from photos taken during a visit to Austin and from the paper by Kellner and Langston 1996. If I have errors here, please send fresh data.

Earlier (Fig. 3) we looked at feeding strategies of Quetzalcoatlus as a giant wader in deeper waters descending from tiny waders, like n42 and n44, in shoreline waters. The degree of flexion and extension in the model corresponds well with that found by Averianov 2013, who did not consider this mode of predation.

It’s also a fact that the largest azhdarchids. like Quetzalcoatlus, had the relatively longest necks (compare to Zhejiangopterus, fig. 2), for instance), which increased their terrestrial height. Earlier we discussed the possibility that taller azhdarchids were preferred in mating rituals. You can get taller by elongating the neck or increasing the overall size or both. Apparently azhdarchids did both. As Averianov mentioned in personal correspondence, you don’t need such a long neck for any type of feeding method, particularly dipping and probing. It just comes with the program — like deer antlers.

Quetzalcoatlus scraping bottom while standing in shallow water.

Figure 3. Quetzalcoatlus scraping bottom while standing in semi-shallow water.

I would agree with others who say azhdarchids were unlikely to be soaring beak dippers in the pattern of pelicans. The gular (throat) sac was too far removed from the beak tip and the beak tip itself was fragile, like the end of a yardstick, and not at all streamlined for plowing or skimming through water. (Humphries et al. 2007).

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Averianov AO 2013. Reconstruction of the neck of Azhdarcho lancicollis and lifestyle of azhdarchids (Pterosauria, Azhdarchidae). Paleontological Journal 47 (2): 203-209. DOI: 10.1134/S0031030113020020
http://link.springer.com/article/10.1134/S0031030113020020.
Humphries S, Bonser RHC, Witton MP, Martill DM 2007. Did Pterosaurs Feed by Skimming? Physical Modelling and Anatomical Evaluation of an Unusual Feeding Method. PLoS Biol 5(8): e204. doi:10.1371/journal.pbio.0050204
Nesov LA1984. Upper Cretaceous pterosaurs and birds from Central Asia. Paleontologicheskii Zhurnal, 1984(1), 47-57.

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