Creature Feature 15

This is the 15th week of Creature Features - it's hard to believe it's been so long already! At this point we've already looked at most of the well-described species from Hell Creek, so some of the future Creature Features may not be able to go as in-depth due to lack of information on some of the other organisms found in Hell Creek that are known from very fragmentary material. However, I will do my best to give whatever info I can! We still have a few decently-described species to cover, so those will be done first.

Anyways, this week's Creature Feature will be looking at the family Azhdarchidae as a whole.

Azhdarchid model, based mostly on Quetzalcoatlus, WIP. Pycnofibers will be added.

The reason that this creature feature will be looking at the family as a whole is because while the remains found from Hell Creek are thought to be those of Quetzalcoatlus, they are not diagnostic at the generic level and as such we can only be sure that the Hell Creek pterosaur was an Azhdarchid (Henderson and Peterson, 2006).

Azhdarchids were a group of pterosaurs that included some of the largest animals ever to roam the skies. They were among the pterosaurs that lasted until the very end of the Cretaceous - originally it was thought that most pterosaur families had already gone extinct towards the end of the Cretaceous, but more recent evaluations suggest a significant diversity of pterosaur fauna (Agnolin and Varricchio, 2012).

There are several distinctive features in Azhdarchid pterosaurs, including large heads with eyes placed just behind a large nasal foramen (likely to reduce the weight of the skull), extremely long and toothless jaws, a long neck, and stiltlike limbs (Averianov, 2013). As has been stated, some of the more recent members grew to truly immense sizes - up to 13m wingspans, yet weighed only an estimated 70-85kg (Witton, 2007). Unfortunately, many Azhdarchids are only known from very fragmentary remains, making it very difficult to completely reconstruct their anatomy, and many localities are like Hell Creek in that the remains are not diagnostic at the generic level (Averianov, 2013). However, the most complete collection of bones preserved with a minimal amount of flattening belong to Quetzalcoatlus, though only the cranial material of this collection has been described (Kellner and Langston, 1996). The shape of the jaw also suggests the presence of a throat sac (Kellner and Langston, 1996; Averianov, 2010).

The biology and behavior of Azhdarchids was a subject of much controversy for a long time due to the fragmentary nature of most remains, as well as the lack of suitable modern analogs and relative scarcity of materials (Averianov, 2013). Originally, it was suggested that Azhdarchids were skimmers (Nesov, 1984; Kellner and Langston, 1996), but more recent analyses seem to show that this is unlikely. Recent research shows that Azhdarchids did not possess the necessary adaptations for a skimming lifestyle, and may have fed like modern storks or ground hornbills - foraging for small animals or carrion in a variety of environments (Witton and Naish, 2008). However, Averianov (2013) hypothesizes that Azhdarchids would fly slowly over the surface of large water bodies (such as rivers and lakes, and possibly sea coasts), scanning for fish or small shoals of fish. When it saw potential prey, they would open the mouth, which would expand their throat sac due to their spiral jaw joint. They would use this as a scoop net, capturing the prey and throwing their head back quickly and swallowing their prey.

Well, I hope this has taught you a little bit more about this most fascinating group of pterosaurs!

Acknowledgements:

Henderson, M.D. and Peterson, J.E. 2006. An azhdarchid pterosaur cervical vertebra from the Hell Creek Formation (Maastrichtian) of southeastern Montana. Journal of Vertebrate Paleontology 26(1): 192–195.

Agnolin, Federico L. and Varricchio, David. 2012. Systematic reinterpretation of Piksi barbarulna Varricchio, 2002 from the Two Medicine Formation (Upper Cretaceous) of Western USA (Montana) as a pterosaur rather than a bird (PDF). Geodiversitas 34 (4): 883-894.

Averianov, A. O. 2013. Reconstruction of the neck of Azhdarcho lancicollis and lifestyle of azhdarchids (Pterosauria, Azhdarchidae). Paleontological Journal 47 (2): 203-209.

Witton, M.P. 2007. Titans of the Skies: Azhdarchid Pterosaurs. Geol. Today 23 (1): 33-38.

Kellner, Alexander W. A.; Langston, W. 1996. Cranial Remains of Quetzalcoatlus (Pterosauria, Azhdarchidae) from Late Cretaceous Sediments of Big Bend National Park, Texas. Journal of Vertebrate Paleontology, 16(2), 222–231.

Averianov, A. O. 2010. The Osteology of Azhdarcho lancicollis Nessov, 1984 (Pterosauria, Azhdarchidae) from the Late Cretaceous of Uzbekistan. Proc. Zool. Inst. Russ. Acad. Sci., 314 (3): 264-317.

Nesov, L. A. 1984. Upper Cretaceous pterosaurs and birds from Central Asia. Paleontologicheskii Zhurnal 1984 (1): 47-57.

Witton M. P.; Naish, D. 2008 A Reappraisal of Azhdarchid Pterosaur Functional Morphology and Paleoecology. PLoS ONE 3(5): e2271.