Azhdarchids

Azhdarchidae (from the Persian word , , a dragon-like creature in Persian mythology) 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 (late Berriasian age, about 140 million years ago). Azhdarchids include some of the largest flying animals discovered, but smaller cat-size members have also been found. Originally considered a sub-family of Pteranodontidae, Nesov (1984) named the Azhdarchinae to include the pterosaurs ''Azhdarcho'', ''Quetzalcoatlus'', and ''Titanopteryx'' (now known as ''Arambourgiania''). They were among the last known surviving members of the pterosaurs, and were a rather successful group with a worldwide distribution. Previously it was thought that by the end of the Cretaceous, most pterosaur families except for the Azhdarchidae disappeared from the fossil record, but recent studies indicate a wealth of pterosaurian fauna, including pteranodontids, nyctosaurids, tapejarids and several indeterminate forms.

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 bodyplan, the 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 (nicknamed "Dracula" by paleontologists), 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 (which include filter-feeders like ''Ctenochasma'' and ''Pterodaustro''), but this classification is largely obsolete. Currently it is widely agreed that azhdarchids were closely related to pterosaurs such as chaoyangopterids, thalassodromids, and tapejarids, all of which belong to the superfamily Azhdarchoidea.

Phylogeny

Two of the most complete cladograms that include the family Azhdarchidae are presented below. The first one is by Brian Andres in 2021, in which Azhdarchidae was found to be the sister taxon to ''Montanazhdarcho'' within the clade Azhdarchiformes. Within Azhdarchidae, two different subfamilies were recovered, the Azhdarchinae and the Quetzalcoatlinae. The former contains azhdarchids closer related to ''Azhdarcho'' and are smaller in size, while the latter contains azhdarchids closer to ''Quetzalcoatlus'' and are much larger in size. The second cladogram is by Xuanyu Zhou and colleagues in 2024, which is based on the phylogenetic analysis by Rodrigo Pêgas in the same year. In this study, Azhdarchidae was recovered as the sister taxon to the family Alanqidae within the clade Azhdarchiformes. The subfamily Quetzalcoatlinae comprised more azhdarchid genera within it, while the subfamily Azhdarchinae was not recovered. Various azhdarchids found within the Quetzalcoatlinae by Andres in 2021 have been found outside said subfamily in this study. These include ''Aralazhdarcho'', ''Eurazhdarcho'', ''Wellnhopterus'', and ''Phosphatodraco'', which together form a subgroup, as well as ''Zhejiangopterus'', ''Mistralazhdarcho'', and ''Aerotitan'', which form another subgroup. ''Azhdarcho'' is recovered as the sister taxon to Quetzalcoatlinae, while ''Albadraco'' was found within Quetzalcoatlinae instead of Azhdarchinae.

Topology 1: Andres (2021).

Topology 2: Zhou and colleagues (2024).

Former and possible azhdarchid genera

There have been many pterosaur genera that were once assigned to the Azhdarchidae, but have since been reassigned to other pterosaur groups. ''Alanqa'' and ''Argentinadraco'', for example, have sometimes been referred to Azhdarchidae, but recent phylogenetic studies have recovered these as either forming their own family, the Alanqidae, or within the family Thalassodromidae. The genus ''Bakonydraco'', also initially classified as an azhdarchid, has been recovered as a tapejarid in many recent studies. ''Volgadraco'' and ''Bogolubovia'', both assigned to this family in at least one study, are currently considered pteranodontians. The pterosaur ''Montanazhdarcho'' has also been reclassified as a non-azhdarchid, with phylogenetic analyses recovering it as either an alanqid, or as a basal azhdarchiform.

The genus ''Navajodactylus'' was tentatively assigned to this family, but its status has been questioned.Wilton, Mark P. (2013). Pterosaurs: Natural History, Evolution, Anatomy. Princeton University Press. . The pterosaur ''Tethydraco'' has been suggested to have been an azhdarchid in one study, but this assignment has not been found in other analyses, with most finding it as a pteranodontian.

References

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{{Taxonbar, from=Q134363

Berriasian first appearances
Maastrichtian extinctions
Pterosaur families