Epipophyses

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Skull and neck vertebrae of the abelisaurid theropod Carnotaurus with clearly visible epipophyses. In this genus, the epipophyses are greatly enlarged.

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]

References

  1. ^ a b c d e f g Brusatte, Stephen L. (2012). Dinosaur Paleobiology (1. ed.). New York: Wiley, J. p. 14. ISBN 978-0-470-65658-7.
  2. ^ Currie, Philip J. (1997). "Theropoda". In Philip J. Currie, Kevin Padian. Encyclopedia of dinosaurs. Acad. Press. p. 734. ISBN 978-0-12-226810-6.CS1 maint: Uses editors parameter (link)
  3. ^ Nesbitt, S.J. (2011). "The early evolution of archosaurs: relationships and the origin of major clades" (PDF). Bulletin of the American Museum of Natural History. 352: 1–292. doi:10.1206/352.1. hdl:2246/6112.
  4. ^ Nesbitt, Sterling J.; Butler, Richard J.; Ezcurra, Martin D.; Charig, Alan J.; Barrett, Paul M. (2018). "The anatomy of Teleocrater Rhadinus, an early avemetatarsalian from the lower portion of the Lifua Member of the Manda Beds (Middle Triassic)". Journal of Vertebrate Paleontology. 37 (sup1): 142–177. doi:10.1080/02724634.2017.1396539.
  5. ^ Nesbitt, S. J.; Stocker, M. R.; Small, B. J.; & A. Downs (November 26, 2009). "The osteology and relationships of Vancleavea campi (Reptilia: Archosauriformes)". Zoological Journal of the Linnean Society. 157 (4): 814–864. doi:10.1111/j.1096-3642.2009.00530.x.CS1 maint: Multiple names: authors list (link)
  6. ^ Sookias, Roland B.; Sullivan, Corwin; Liu, Jun; Butler, Richard J. (2014-11-25). "Systematics of putative euparkeriids (Diapsida: Archosauriformes) from the Triassic of China". PeerJ. 2: e658. doi:10.7717/peerj.658. ISSN 2167-8359. PMC 4250070. PMID 25469319.
  7. ^ Montefeltro, Felipe Chinaglia; Bittencourt, Jonathas Souza; Langer, Max Cardoso; Schultz, Cesar Leandro (January 2013). "Postcranial anatomy of the hyperodapedontine rhynchosaurTeyumbaita sulcognathus(Azevedo and Schultz, 1987) from the Late Triassic of Southern Brazil". Journal of Vertebrate Paleontology. 33 (1): 67–84. doi:10.1080/02724634.2012.710285. ISSN 0272-4634.
  8. ^ Pritchard, Adam C.; Turner, Alan H.; Nesbitt, Sterling J.; Irmis, Randall B.; Smith, Nathan D. (2015-03-04). "Late Triassic tanystropheids (Reptilia, Archosauromorpha) from northern New Mexico (Petrified Forest Member, Chinle Formation) and the biogeography, functional morphology, and evolution of Tanystropheidae". Journal of Vertebrate Paleontology. 35 (2): e911186. doi:10.1080/02724634.2014.911186. ISSN 0272-4634.
  9. ^ Nesbitt, Sterling J.; Flynn, John J.; Pritchard, Adam C.; Parrish, J. Michael; Ranivoharimanana, Lovasoa; Wyss, André R. (2015-12-07). "Postcranial Osteology of Azendohsaurus madagaskarensis (?Middle to Upper Triassic, Isalo Group, Madagascar) and its Systematic Position Among Stem Archosaur Reptiles" (PDF). Bulletin of the American Museum of Natural History. 398: 1–126. doi:10.5531/sd.sp.15. hdl:2246/6624. ISSN 0003-0090.
  10. ^ Taylor, Mike (2015-02-02). "Epipophyses, the forgotten apophyses: not just for sauropods!". Sauropod Vertebra Picture of the Week.
  11. ^ Taylor, Mike (2015-02-05). "The equivocal epipophyses of Cf. Quetzalcoatlus". Sauropod Vertebra Picture of the Week.
  12. ^ Taylor, Mike (2015-02-04). "Further exciting developments in the field of non-sauropod epipophyses". Sauropod Vertebra Picture of the Week.
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