Epipophyses are bony projections of the

cervical vertebrae In tetrapods, cervical vertebrae (singular: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In ...

found in

archosauromorphs Archosauromorpha (Greek for "ruling lizard forms") is a clade of diapsid reptiles containing all reptiles more closely related to archosaurs (such as crocodilians and dinosaurs, including birds) rather than lepidosaurs (such as tuataras, liz ...

, particularly

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

s (including some basal

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...

s). These paired processes sit above the

postzygapophyses The articular processes or zygapophyses ( Greek ζυγον = " yoke" (because it links two vertebrae) + απο = "away" + φυσις = " process") of a vertebra are projections of the vertebra that serve the purpose of fitting with an adjacent vert ...

on the rear of the vertebral

neural arch 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 characteristic ...

. Their morphology is variable and ranges from small, simple, hill-like elevations to large, complex, winglike projections. Epipophyses provided large attachment areas for several neck muscles; large epipophyses are therefore indicative of a strong neck musculature. The presence of epipophyses is a

synapomorphy In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...

(distinguishing feature) of the group Dinosauria. Epipophyses were present in the basal-most dinosaurs, but absent in the closest relatives of the group, such as ''

Marasuchus ''Marasuchus'' (meaning "Mara crocodile") is a genus of basal dinosauriform archosaur which is possibly synonymous with '' Lagosuchus''. Both genera lived during the Late Triassic in what is now La Rioja Province, Argentina. ''Marasuchus'' conta ...

'' and '' Silesaurus''. They were typical for most dinosaur lineages; however, they became lost in several derived

theropod Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...

lineages in the wake of an increasingly S-shaped curvature of the neck. Several scientific papers have observed that epipophyses were present in various non-dinosaur archosauromorphs. These include several

pseudosuchia Pseudosuchia is one of two major divisions of Archosauria, including living crocodilians and all archosaurs more closely related to crocodilians than to birds. Pseudosuchians are also informally known as "crocodilian-line archosaurs". Prior to ...

ns (''

Batrachotomus ''Batrachotomus'' is a genus of prehistoric archosaur. Fossils of this animal have been found in southern Germany and dated from the Ladinian stage of the Middle Triassic period, around 242 to 237 million years ago. ''Batrachotomus'' was descr ...

'', ''

Revueltosaurus ''Revueltosaurus'' ("Revuelto lizard") is an extinct genus of suchian pseudosuchian from Late Triassic (late Carnian to middle Norian stage) deposits of New Mexico, Arizona and North Carolina, United States. Many specimens, mostly teeth, have bee ...

Xilousuchus ''Xilousuchus'' is an extinct genus of poposauroid from lower Triassic (Olenekian stage) deposits of Fugu County of northeastern Shanxi Province, China. It is known from the holotype, IVPP V 6026, a single well-preserved partial skelet ...

Effigia ''Effigia'' was an Extinction, extinct genus of Shuvosauridae, shuvosaurid known from the Late Triassic of New Mexico, south-western USA. With a bipedal stance, long neck, and a toothless beaked skull, ''Effigia'' and other shuvosaurids bore a re ...

, Hesperosuchus''), basal

avemetatarsalia Avemetatarsalia (meaning "bird metatarsals") is a clade of diapsid reptiles containing all archosaurs more closely related to birds than to crocodilians. The two most successful groups of avemetatarsalians were the dinosaurs and pterosaurs. ...

ns ( aphanosaurs) non-archosaur

archosauriforms Archosauriformes (Greek for 'ruling lizards', and Latin for 'form') is a clade of diapsid reptiles that developed from archosauromorph ancestors some time in the Latest Permian (roughly 252 million years ago). It was defined by Jacques Gauthi ...

('' Vancleavea'', ''

Halazhaisuchus ''Halazhaisuchus'' is an extinct genus of archosauriform from the Early Triassic of China. It is known from a single species, ''Halazhaisuchus qiaoensis'', which was named in 1982 from the lower Ermaying Formation in Shaanxi. It was assigned to ...

''),

rhynchosaur Rhynchosaurs are a group of extinct herbivorous Triassic archosauromorph reptiles, belonging to the order Rhynchosauria. Members of the group are distinguished by their triangular skulls and elongated, beak like premaxillary bones. Rhynchosaurs ...

s, several tanystropheids, and allokotosaurs. Sauropod-oriented paleontologist Mike Taylor has informally suggested that epipophyses were also present in the vertebrae of certain

pterosaur Pterosaurs (; from Greek ''pteron'' and ''sauros'', meaning "wing lizard") is an extinct clade of flying reptiles in the order, Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous (228 to ...

References

{{cite book , editor=Philip J. Currie , editor2=Kevin Padian , first=Philip J. , last=Currie , chapter=Theropoda , title=Encyclopedia of dinosaurs , publisher=Acad. Press , isbn=978-0-12-226810-6 , year=1997, page=734 Dinosaur anatomy