Azhdarchoidea was named by paleontologist David Unwin in 1995. He later gave the clade a phylogenetic definition in 2003. He defined the group as the most recent common ancestor of
Quetzalcoatlus and
Tapejara, and all its descendants. Some researchers also consider an additional grouping,
Alanqidae, composed of taxa formerly considered azhdarchids. Other earlier studies, such as that of paleontologists
Darren Naish &
David Martill in 2006, and that of
Lü Junchang and colleagues in 2008, considered the traditional "tapejarids" to be a
paraphyletic grade of primitive azhdarchoids, with true tapejarids more basal, and the thalassodromines (alternatively called thalassodromids) and chaoyangopterids being successively more closely related to
azhdarchids. Generally speaking, in the modern scientific literature, there are two major competing hypotheses regarding the classification of azhdarchoids. The first of these is based on the work of Brian Andres and colleagues, who have published multiple papers on the taxa
Kryptodrakon,
Elanodactylus, and
Quetzalcoatlus among others, in which they examined the phylogenetic relationships of these groups. Andres and colleagues have generally suggested that
Dsungaripteridae and
Thalassodromidae are closely related and that they form a clade (Dsungaripteromorpha) which is more closely related to
Azhdarchidae than
Tapejaridae. This result has been corroborated by some other authors. A simplified version of Andres and colleagues' phylogeny is shown below. This hypothesis has also received support from other authors. A simplified version of their results is shown below. }}
Subclades A wide variety of subclades have been defined within Azhdarchoidea in the last 15 years. Many of these have contradictory or overlapping definitions, and so whether or not these clades represent true
monophyletic groups remains hotly debated. Some of the uncertainty regards the position of
Thalassodromidae, which may be closely related to either
Tapejaridae or
Dsungaripteridae. Another source of uncertainty is the affinities of the dsungaripterids themselves. This problematic group has been found to be closely related to
Ornithocheiromorpha, just outside of Azhdarchoidea, or within Azhdarchoidea. ==See also==