Enter the dragons: the phylogeny of Azhdarchoidea (Pterosauria: Pterodactyloidea) and the evolution of giant size in pterosaurs

Azhdarchidae is a clade of pterosaurs which includes the largest-ever flying animals. The evolutionary history of this clade and its closest relatives remains incompletely understood and highly debated. To investigate this, we combined multiple preexisting datasets with 29 new operational taxonomic units and 57 new characters, resulting in the most comprehensive phylogenetic analysis of pterosaurs published to date, with a focus on Azhdarchomorpha. Higher level phylogenetic taxonomy of Azhdarchomorpha is revised based on the results of this analysis, and three new clade names are established: Shenzhoupterinae (cl. nov.) for the subgroup of Chaoyangopteridae containing Shenzhoupterus that is sister to the existing Chaoyangopterinae; Concilazhia (cl. nov.) for the clade uniting Chaoyangopteridae and Azhdarchiformes; and Serpennata (cl. nov.) for the clade with highly elongated cervical series that includes the giant (∼10 m wingspan) Quetzalcoatlus and Arambougiania. The iconic genus Quetzalcoatlus is recovered as polyphyletic, with its giant and moderately large species belonging to separate clades within Serpennata. Gigantism evolved convergently at least four times in quetzalcoatline azhdarchids: in Cryodrakon, once in a clade containing Hatzegopteryx and its closest relatives, and twice independently in different lineages of Serpennata.