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2011 | 56 | 4 |
Tytuł artykułu

Morphology and evolutionary significance of the atlas-axis complex in varanopid synapsids

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Warianty tytułu
Języki publikacji
EN
Abstrakty
EN
The atlas−axis complex has been described in few Palaeozoic taxa, with little effort being placed on examining variation of this structure within a small clade. Most varanopids, members of a clade of gracile synapsid predators, have well preserved atlas−axes permitting detailed descriptions and examination of morphological variation. This study indicates that the size of the transverse processes on the axis and the shape of the axial neural spine vary among members of this clade. In particular, the small mycterosaurine varanopids possess small transverse processes that point posteroventrally, and the axial spine is dorsoventrally short, with a flattened dorsal margin in lateral view. The larger varanodontine varanopids have large transverse processes with a broad base, and a much taller axial spine with a rounded dorsal margin in lateral view. Based on outgroup comparisons, the morphology exhibited by the transverse processes is interpreted as derived in varanodontines, whereas the morphology of the axial spine is derived in mycterosaurines. The axial spine anatomy of Middle Permian South African varanopids is reviewed and our interpretation is consistent with the hypothesis that at least two varanopid taxa are present in South Africa, a region overwhelmingly dominated by therapsid synapsids and parareptiles.
Słowa kluczowe
Wydawca
-
Rocznik
Tom
56
Numer
4
Opis fizyczny
p.739-748,fig.,ref.
Twórcy
  • Department of Ecology and Evolutionary Biology, University of Toronto, 100 Queen’s Park, Toronto, Ontario, Canada M5S 2C6
autor
  • Department of Biology, University of Toronto Mississauga, 3359 Mississauga Rd. N., Mississauga, Ontario, Canada L5L 1C6
Bibliografia
  • Botha−Brink, J. and Modesto, S.P. 2007. A mixed−age classed “pelycosaur” aggregation from South Africa: earliest evidence of parental care in amniotes? Proceedings of the Royal Society B 274: 2829–2834.
  • Botha−Brink, J. and Modesto, S.P. 2009. Anatomy and relationships of the Middle Permian varanopid Heleosaurus scholtzi based on a social aggregation from the Karoo Basin of South Africa. Journal of Vertebrate Paleontology 29: 389–400.
  • Campione, N.E. and Reisz, R.R. 2010. Varanops brevirostris (Eupelycosauria: Varanopidae) from the Lower Permian of Texas with discussion of varanopid morphology and interrelationships. Journal of Vertebrate Paleontology 30: 724–746.
  • Carroll, R.L. 1976. Eosuchians and the origin of archosaurs. In: C.S. Churcher (ed.), Athlon: Essays on Palaeontology in Honour of Loris Shano Russell, 58–79. Miscellaneous Publications of the Royal Ontario Museum, Toronto.
  • Case, E.C. and Williston, S.W. 1913. Description of certain collections of bones referred to Sphenacodon Marsh. Permo−Carboniferous Vertebrates from New Mexico. Carnegie Institution of Washington 181: 61–70.
  • Dilkes, D.W. and Reisz, R.R. 1996. First record of a basal synapsid (‘mammal−like reptile’) in Gondwana. Proceedings of the Royal Society of London B 263: 1165–1170.
  • Evans, D.C., Maddin, H.C., and Reisz, R.R. 2009. A re−evaluation of sphenacodontid synapsid material from the Lower Permian fissue fills near Richards Spur, Oklahoma. Palaeontology 52: 219–227.
  • Godfrey, S.J. and Reisz, R.R. 1991. The vertebral morphology of Gephyrostegus bohemicus Jaekel 1902, with comments on the atlas−axis complex in primitive tetrapods. Historical Biology 5: 27–36.
  • Laurin, M. 1993. Anatomy and relationships of Haptodus garnettensis, a Pennsylvanian synapsid from Kansas. Journal of Vertebrate Paleontology 13: 200–229.
  • Maddin, H.C., Evans, D.C., and Reisz, R.R. 2006. An Early Permian varanodontine varanopid (Synapsida: Eupelycosauria) from the Richards Spurs locality, Oklahoma. Journal of Vertebrate Paleontology 26: 957–966.
  • Modesto, S., Sidor, C.A., Rubidge, B.S., and Welman, J. 2001. A second varanopseid skull from the Upper Permian of South Africa: implications for Late Permian “pelycosaur” evolution. Lethaia 34: 249–259.
  • R−Development−Core−Team 2010. R: A Language and Environment for Statistical Computing, Version 2.12.0. R Foundation for Statistical Computing, Vienna, Austria.
  • Rasband, W. 2007. ImageJ, Version Version 1.38x. National Institutes of Health, Bethesda, Maryland.
  • Reisz, R.R. and Berman, D.S. 2001. The skull of Mesenosaurus romeri, a small varanopseid (Synapsida: Eupelycosauria) from the Upper Permian of the Mezen River Basin, Northern Russia. Annals of Carnegie Museum 70: 113–132.
  • Reisz, R.R. and Dilkes, D.W. 1992. The taxonomic position of Anningia megalops, a small amniote from the Permian of South Africa. Canadian Journal of Earth Sciences 29: 1605–1608.
  • Reisz, R.R. and Dilkes, D.W. 2003. Archaeovenator hamiltonensis, a new varanopid (Synapsida: Eupelycosauria) from the Upper Carboniferous of Kansas. Canadian Journal of Earth Sciences 40: 667–678.
  • Reisz, R.R. and Laurin, M. 2004. A reevaluation of the enigmatic Permian synapsid Watongia and of its stratigraphic significance.Canadian Journal of Earth Sciences 41: 377–386.
  • Reisz, R.R. and Modesto, S.P. 2007. Heleosaurus scholtzifrom the Permian of South Africa: a varanopid synapsid, not a diapsid reptile. Journal of Vertebrate Paleontology 27: 234–239.
  • Reisz, R.R., Dilkes, D.W., and Berman, D.S. 1998. Anatomy and relationships of Elliotsmithia longiceps Broom, a small synapsid (Eupelycosauria: Varanopseidae) from the Late Permian of South Africa. Journal of Vertebrate Paleontology 18: 602–611.
  • Reisz, R.R., Laurin, M., and Marjanovic, D. 2010. Apsisaurus witteri from the Lower Permian of Texas: yet another small varanopid synapsid, not a diapsid. Journal of Vertebrate Paleontology 30: 1628–1631.
  • Reisz, R.R., Scott, D., and van Bendegem, J. 1992. Atlas−axis complex of Secodontosaurus, a sphenacodontid mammal−like reptile (Eupelycosauria: Synapsida) from the Lower Permian of Texas. Canadian Journal of Earth Sciences 29: 596–600.
  • Reisz, R.R., Wilson, H., and Scott, D. 1997. Varanopseid synapsid skeleton elements from Richard Spur, a Lower Permian fissure fill near Fort Sill, Oklahoma. Oklahoma Geology Notes 57 (5): 160–170.
  • Romer, A.S. 1956. Osteology of the Reptiles. 772 pp. The University of Chicago Press, Chicago.
  • Romer, A.S. and Price, L.I. 1940. Review of the Pelycosauria. Geological Society of America Special Paper 28: 1–538.
  • Stovall, J.W., Price, L.I., and Romer, A.S. 1966. The postcranial skeleton of the giant Permian pelycosaur Cotylorhynchus romeri. Bulletin of the Museum of Comparative Zoology 135: 1–30.
  • Sumida, S.A., Lombard, R.E., and Berman, D.S. 1992. Morphology of the atlas−axis complex of the late Palaeozoic tetrapod suborders Diadectomorpha and Seymouriamorpha. Philosophical Transactions of the Royal Society of London, Series B 336: 259–273.
  • Williston, S.W. 1911. American Permian Vertebrates. 145 pp. University of Chicago Press, Chicago.
Typ dokumentu
Bibliografia
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Identyfikator YADDA
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