Epipophyses are bony projections of the cervical vertebrae found in archosauromorphs, particularly dinosaurs (including some basal birds). [1] These paired processes sit above the postzygapophyses on the rear of the vertebral neural arch. [1] Their morphology is variable and ranges from small, simple, hill-like elevations to large, complex, winglike projections. [1] Epipophyses provided large attachment areas for several neck muscles; large epipophyses are therefore indicative of a strong neck musculature. [1]
The presence of epipophyses is a synapomorphy (distinguishing feature) of the group Dinosauria. [1] Epipophyses were present in the basal-most dinosaurs, but absent in the closest relatives of the group, such as Marasuchus and Silesaurus . [1] They were typical for most dinosaur lineages; however, they became lost in several derived theropod lineages in the wake of an increasingly S-shaped curvature of the neck. [1] [2]
Several scientific papers have observed that epipophyses were present in various non-dinosaur archosauromorphs. These include several pseudosuchians ( Batrachotomus , Revueltosaurus, Xilousuchus, Effigia, Hesperosuchus ), [3] basal avemetatarsalians (aphanosaurs) [4] non-archosaur archosauriforms ( Vancleavea , [5] Halazhaisuchus [6] ), rhynchosaurs, [7] several tanystropheids, [8] and allokotosaurs. [9] Sauropod-oriented paleontologist Mike Taylor has informally suggested that epipophyses were also present in the vertebrae of certain pterosaurs. [10] [11] [12]