Azhdarchidae

Artist Mark Witton's reconstruction of Hatzegopteryx hunting the ornithopod Zalmoxes.

Hatzegopteryx (A-B) compared with Arambourgiania (C) and Quetzalcoatlus (D-E). This illustrates the difference between the "blunt-beaked" azhdarchids and the "slender-beaked" forms.

Azhdarchids are characterized by their long legs and extremely long necks, made up of elongated neck vertebrae which are round in cross section. Most species of azhdarchids are still known mainly from their distinctive neck bones and not much else. The few azhdarchids that are known from reasonably good skeletons include Zhejiangopterus and Quetzalcoatlus. Azhdarchids are also distinguished by their relatively large heads and long, spear-like jaws. There are two major types of azhdarchid morphologies: the "blunt-beaked" forms with shorter and deeper bills and the "slender-beaked" forms with longer and thinner jaws.[9]

It had been suggested azhdarchids were skimmers,[3][10] but further research has cast doubt on this idea, demonstrating that azhdarchids lacked the necessary adaptations for a skim-feeding lifestyle, and that they may have led a more terrestrial existence similar to modern storks and ground hornbills.[11][12][13][14][15] Most large azhdarchids probably fed on small prey, including hatchling and small dinosaurs; in an unusual modification of the azhdarchid bodyplan, the robust Hatzegopteryx may have tackled larger prey as the apex predator in its ecosystem.[16] In another departure from typical azhdarchid lifestyles, the jaw of Alanqa may possibly be an adaptation to crushing shellfish and other hard foodstuffs.[17]

Azhdarchids are generally medium- to large-sized pterosaurs, with the largest achieving wingspans of 10–12 metres (33–39 ft),[18] but several small-sized species have recently been discovered.[19][20] Another azhdarchid that is currently unnamed, recently discovered in Transylvania, may be the largest representative of the family thus far discovered. This unnamed specimen (nicknamed "Dracula" by paleontologists), currently on display in the Altmühltal Dinosaur Museum in Bavaria is estimated to have a wingspan of 12–20 m (39–66 ft), although similarities to the contemporary azhdarchid Hatzegopteryx have also been noted.[21]

Azhdarchids were originally classified as close relatives of Pteranodon due to their long, toothless beaks. Others have suggested they were more closely related to the toothy ctenochasmatids (which include filter-feeders like Ctenochasma and Pterodaustro). Currently it is widely agreed that azhdarchids were closely related to pterosaurs such as Tupuxuara and Tapejara.

Taxonomy

Classification after Unwin 2006, except where noted.[22]

Reconstructed feeding posture of an azhdarchid with sagittally aligned limbs.

• Family Azhdarchidae
  • Aerotitan
  • Alanqa[23]
  • Aralazhdarcho[24]
  • Arambourgiania
  • Azhdarcho
  • Cretornis[25]
  • Eurazhdarcho[26]
  • Hatzegopteryx
  • Mistralazhdarcho[27]
  • Montanazhdarcho?[6]
  • Palaeocursornis
  • Phosphatodraco
  • Quetzalcoatlus
  • Volgadraco[28]
  • Zhejiangopterus
  • Possible valid azhdarchid genera
    • Argentinadraco? (azhdarchoid, tentatively classified as an azhdarchid)[29]
    • Bennettazhia
    • Bogolubovia
    • Navajodactylus?

• Astibia, H.; Buffetaut, E.; Buscalioni, A.D.; Cappetta, H.; Corral, C.; Estes, R.; Garcia-Garmilla, F.; Jaeger, Mazin; Jimenez-Fuentes, J.J.; Loeuff, J. Le; Mazin, J.M.; Orue-Etxebarria, X.; Pereda-Suberbiola, J.; Powell, J.E.; Rage, J.C.; Rodriguez-Lazaro, J.; Sanz, J.L.; Tong, H.; et al. (1991). "The fossil vertebrates from Lafio (Basque Country, Spain); new evidence on the composition and affinities of the Late Cretaceous continental fauna of Europe". Terra Nova. 2 (5): 460–466. doi:10.1111/j.1365-3121.1990.tb00103.x.
• Bennett, S. C. (2000). "Pterosaur flight: the role of actinofibrils in wing function". Historical Biology. 14 (4): 255–284. doi:10.1080/10292380009380572. S2CID 85185457.
• Nesov, L.A. (1990). "Flying reptiles of the Jurassic and Cretaceous of the USSR and the significance of their remains for the reconstruction of palaeogeographic conditions". Bulletin of Leningrad University, Series 7, Geology and Geography (in Russian). 4 (28): 3–10.
• Nesov, L.A. (1991). "Giant flying reptiles of the family Azhdarchidae: 11. Environment, sedirnentological conditions and preservation of remains". Bulletin of Leningrad University, Series 7, Geology and Geography (in Russian). 3 (21): 16–24.