page_title: Istiodactylus
section_title: Classification
hierarchical_section_title: Istiodactylus / Classification
caption_attribution_description: Various bones ofIstiodactylus latidens, including back of skull, notarium, and neck vertebra.
context_page_description: Istiodactylus is a genus of pterosaur that lived during the Early Cretaceous period, about 120 million years ago. The first fossil was discovered on the English Isle of Wight in 1887, and in 1901 became the holotype specimen of a new species, O. latidens, in the genus Ornithodesmus. This species was moved to its own genus, Istiodactylus, in 2001; this name is Greek for "sail finger". More specimens were described in 1913, and Istiodactylus was the only pterosaur known from three-dimensionally preserved fossils for much of the 20th century. In 2006, a species from China, I. sinensis, was assigned to Istiodactylus, but it has since been found to belong to a different genus.
  Istiodactylus was a large pterosaur; estimates of its wingspan range from 4.3 to 5 metres. Its skull was about 45 centimetres long, and was relatively short and broad for a pterosaur. The front of the snout was low and blunt, and bore a semicircle of 48 teeth. The triangular teeth were closely spaced, interlocked, and formed a "razor-edged" outline. The lower jaw also had a tooth-like projection that occluded with the teeth. The skull had a very large naso-antorbital opening and a slender eye socket.
context_section_description: In 1913, Hooley found the skull and teeth of "O." latidens most similar to those of the pterosaurs Scaphognathus and Dimorphodon, and even considered it a modified form of the former. Later writers classified it among the short-tailed pterodactyloids, and from the 1980s and onwards, it was generally found to be closest to Ornithocheirus and Pteranodon, based on computerised phylogenetic analyses. In 2003, two competing schools of pterosaur classification emerged, that of David Unwin and that of Alexander W. Kellner; both found Istiodactylus to be a member of the group Ornithocheiroidea, but the exact configuration and content of this group has varied between studies. Within Ornithocheiroidea, Unwin found Istiodactylidae (which at the time only consisted of Istiodactylus) to group with the toothless Pteranodontidae, whereas Kellner found the family to group with the toothed Ornithocheiridae. In 2014, Brian Andres and colleagues placed Istiodactylidae in the clade Lanceodontia, which consists of the toothed ornithocheiromorphs, to the exclusion of forms like Pteranodon.
  Since additional members of the family Istiodactylidae were discovered only in the 21st century, with many of those discoveries occurring in quick succession, the interrelationships and exact content of the group are still unclear and need reappraisal. In 2014, Andres and colleagues placed I. latidens, I. sinensis, and Liaoxipterus in a new subfamily within Istiodactylidae, which they called Istiodactylinae. In 2019, Xuanyu Zhou and colleagues found I. latidens and I. sinensis to be sister taxa, and close to Liaoxipterus. In the same year, Kellner and colleagues created the more inclusive group Istiodactyliformes for the family Istiodactylidae and its closest relatives, such as the new family Mimodactylidae, as shown in the cladogram below.
  All istiodactylid remains are known from deposits in the Northern Hemisphere, dating from the Barremian–Aptian ages of the Early Cretaceous period. They are distinguished from other pterosaurs by features such as the shape and position of their teeth, broad snouts, narrowed orbits, and large naso-antorbital fenestrae. In addition to the istiodactylids from China, teeth indicate the presence of the group in Spain and the elsewhere in the UK. Two fossils from North America formerly thought to have been similar to istiodactylids are now believed to have been misidentified; a mandible fragment from the Morrison Formation probably belongs to another pterosaur group, and Gwawinapterus is most likely a fish. Mimodactylus from Lebanon is the first istiodactyliform known from the supercontinent Gondwana.
caption: Illustrations of the occiput, notarium, a neck vertebra, and a shoulder blade of I. latidens, by Woodward, 1913
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