Exapophyses (singular: Exapophysis) are bony joints present in the cervicals (neck

vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characterist ...

e) of some

pterosaur Pterosaurs (; from Greek ''pteron'' and ''sauros'', meaning "wing lizard") is an extinct clade of flying reptiles in the Order (biology), order, Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cre ...

s. Exapophyses lie on the centrum, the spool-shaped main body of each vertebra, where they are positioned adjacent to the main articulating surfaces between centra. Exapophyses which are next to the cotyle (concave front end of the centrum) are known as preexapophyses while those at the condyle (convex rear end) are called postexapophyses. Exapophyses act as accessory articulations, meaning that they complement the cotyle and condyle, as well as the zygapophyses (plate-like joints which lie on the neural arch above the centrum). The term was coined by

Samuel Wendell Williston Samuel Wendell Williston (July 10, 1852 – August 30, 1918) was an American educator, entomologist, and paleontologist who was the first to propose that birds developed flight cursorially (by running), rather than arboreally (by leaping from ...

in 1897 during a description of ''

Pteranodon ''Pteranodon'' (); from Ancient Greek (''pteron'', "wing") and (''anodon'', "toothless") is a genus of pterosaur that included some of the largest known flying reptiles, with ''P. longiceps'' having a wingspan of . They lived during the late C ...

'' (which he called "''Ornithostoma''" at the time). Exapophyses are a defining trait of the pterosaur subgroup

Eupterodactyloidea Eupterodactyloidea (meaning "true Pterodactyloidea") is an extinct group of pterodactyloid pterosaurs that existed from the latest Late Jurassic to the latest Late Cretaceous periods (Tithonian to Maastrichtian stages). Eupterodactyloids lived on ...

, although they are also known to occur in some ctenochasmatids. Rhamphorhynchids have paired, knob-like extensions on the condyle which are occasionally also termed exapophyses, but these extensions are not distinctly offset and are not considered

homologous Homology may refer to: Sciences Biology *Homology (biology), any characteristic of biological organisms that is derived from a common ancestor *Sequence homology, biological homology between DNA, RNA, or protein sequences * Homologous chrom ...

to the exapophyses of eupterodactyloids and ctenochasmatids.

References

{{reflist Pterosaur anatomy