Azhdarchidae is a family of pterosaurs known primarily from the late Cretaceous Period, though an isolated vertebra apparently from an azhdarchid is known from the early Cretaceous as well. Azhdarchids included some of the largest-known flying animalsof all time, but members no larger than a cat have also been found. Originally considered a sub-family of Pteranodontidae, Nesov named the azhdarchinae to include the pterosaurs Azhdarcho, Quetzalcoatlus, and "Titanopteryx". They were among the last known surviving members of the pterosaurs, and were a rather successful group with a worldwide distribution. By the time of the end-Cretaceous mass extinction, most pterosaur families except for the Azhdarchidae disappear from the fossil record, but recent studies indicate a wealth in pterosaurian faunas, including pteranodontids, nyctosaurids, tapejarids and several indeterminate forms. Some taxa like Navajodactylus, Bakonydraco and Montanazhdarcho were moved from Azhdarchidae to other clades.
Description
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. It had been suggested azhdarchids were skimmers, 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. Most large azhdarchids probably fed on small prey, including hatchling and small dinosaurs; in an unusual modification of the azhdarchid bauplan, the unusually robust Hatzegopteryx may have tackled larger prey as the apex predator in its ecosystem. In another departure from typical azhdarchid lifestyles, the jaw of Alanqa may possibly be an adaptation to crushing shellfish and other hard foodstuffs. Azhdarchids are generally medium- to large-sized pterosaurs, with the largest achieving wingspans of, but several small-sized species have recently been discovered. Another azhdarchid that is currently unnamed, recently discovered in Transylvania, may be the largest representative of the family thus far discovered. This unnamed specimen, currently on display in the Altmühltal Dinosaur Museum in Bavaria is estimated to have a wingspan of, although similarities to the contemporary azhdarchid Hatzegopteryx have also been noted.
Systematics
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. 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.
The most complete cladogram of azhdarchids is presented by Longrich et al. : In the analysis, they recovered Aerotitan and Alanqa as thalassodromids, Bennettazhia as a close relative of tapejarids, and Cretornis and Volgadraco as nyctosaurids.
