This phylogeny of pterosaurs entails the various phylogenetic trees used to classify pterosaurs throughout the years and varying views of these animals. Pterosaur phylogeny is currently highly contested and several hypotheses are presented below.
Historical classification
Early theories The earliest discoveries of pterosaurs were partnered with debate over their classification and relatedness to modern animals, beginning with the 1784 description of what would become Pterodactylus as a marine vertebrate of uncertain relationships. Following this, French palaeontologist Georges Cuvier would identify the animal as a reptile; part of some previously unknown flying lineage which is now extinct. Alternative identifications for Pterodactylus around the same time included a waterfowl or a new kind of bat, and even as a form intermediate between birds and flying mammals. Very sparse pterosaur fossils were known throughout the early 19th century, and even beyond Pterodactylus the only other fossil reptiles to compare with were Protorosaurus, an ichthyosaur and a crocodile, and Mosasaurus. The first group name given for pterosaurs was in 1834 when German naturalist Johann Jakob Kaup named Pterosauri for then, which was followed by the names Podoptera, Ornithosauri, Ornithosaurii, Saurornia, Ornithosauria, and Patagiosauria introduced by various other authors. The accepted name for pterosaurs is Pterosauria, a corrected spelling introduced in 1842 by British palaeontologist Richard Owen for the name given by Kaup. Pterosaurs, while classified as an order within Reptilia by Owen, were continuously placed between mammals and reptiles, birds and mammals, or between reptiles and birds, as classification did not account for the possibility that cold-blooded reptiles could include and be ancestral to warm-blooded groups like birds, mammals, and presumably pterosaurs. Internal subdivisions of pterosaurs were first suggested by German palaeontologist Christian Erich Hermann von Meyer in the 1840s but not formalized until 1901 when Rhamphorhynchoidea and Pterodactyloidea were named for the long- and short-tailed pterosaurs respectively. At the time of Meyer's 1846 review of pterosaurs, 16 species had been named, all within the genus Pterodactylus. Despite this, Meyer proposed separating the species of Pterodactylus into different subgenera: he placed one species in the subgenus Ornithopterus on the belief it only had two fingers, and four into the subgenus Rhamphorhynchus for possessing a beak and elongate tail, with the remaining species not placed within a subgenus. The group Diarthri was named for Pterodactylus (Ornithopterus), and Tetrarthri for Pterodactylus and Pterodactylus (Rhamphorhynchus), which itself was separated into Dentirostres for Pterodactylus and Subulirostres for Pterodactylus (Rhamphorhynchus). Similar classification schemes were used by German palaeontologist Andreas Wagner in 1851 to separate the genus Ornithocephalus (an equivalent to Pterodactylus) into "Ornithocephali brevicaudati" and "Ornithocephali longicaudati" species. Meyer maintained his classification in 1860 with the elevation of his subgenera to genus status, and the inclusion of new species named in the elapsed years. In 1870 British palaeontologist Harry Govier Seeley reviewed pterosaurs and the beliefs of previous authors on their classification. From their distinctiveness he named the new group Ornithosauria for them, at the same rank as birds, but conclusively considered them separate from birds. Seeley noted that both a family (Pterodactylæ) and subfamily (Pterodactylinæ) had been named by French naturalist Charles Lucien Bonaparte for Pterodactylus and short-tailed pterosaurs, and that following this precedent the families Rhamphorhynchæ, Dimorphodontæ, and Ornithocheiræ could be named for the existing genera of long-tailed pterosaurs Rhamphorhynchus, Dimorphodon, and Ornithocheirus. This was also followed by the introduction of the suborder Pteranodontia and family Pteranodontidae by American palaeontologist Othniel Charles Marsh in 1876 following the recognition that some species of Pterodactylus were toothless could be moved to their own genus Pteranodon. All these families remain in use in pterosaur systematics, but with modified spellings to reflect their rank.
Early phylogenetics The phylogenetics of pterosaurs remained relatively understudied to assess the accuracy of traditional classifications as exemplified by the 1978 study of Wellnhofer, with only preliminary studies published until the 2000s. The first phylogenetic study was that of Howse in 1986 which only included characters of the cervical vertebrae and was restricted to some pterodactyloids. This was followed by a few iterations of a phylogenetic analysis by Bennett on pterodactyloids which recovered consistent results despite problems with missing data. Reanalysis of these earlier studies by Brazilian palaeontologist Alexander Kellner failed to recover the results that were presented in these studies. The analysis of British palaeontologist David Unwin in 1991 was the first to include a broad array of both pterodactyloid and rhamphorhynchoid pterosaurs, and found that as suspected previously, "rhamphorhynchoids" were an unnatural group that evolved into pterodactyloids. Three pterodactyloid groups, Dsungaripteroidea, Ornithocheiroidea and Azhdarchoidea, were found, with the unique feature of this study being the placement of Pterodactylus and Ctenochasma as azhdarchoids. Unwin and Kellner published additional and revised classifications of pterosaurs throughout the 1990s, with the greatest difference between the two being the relationships of the basalmost pterosaurs. Additional divergent relationships were presented in the late 1990s during conferences that suggested the unity of all toothless pterosaurs within one group, or other unspecified differences, but these results have not been published. Simultaneously in 2003 as part of a Special Publication of the Geological Society of London on the evolution and palaeobiology of pterosaurs, both Kellner and Unwin published updated comprehensive pterosaur phylogenies. They are both shown below, simplified to display broader clade relationships.
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