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Scenella

Scenella
Temporal range: Cambrian Stage 3–Late Ordovician[1]
Dorsal view of the shell of Scenella tenuistriata
lateral view of the shell of Scenella tenuistriata
Scientific classification
Kingdom:
Animalia
Phylum:
Mollusca
Superfamily:
† Scenelloidea
Family:
† Scenellidae

Genus:
Scenella

Billings, 1872
Synonyms[3]
  • Helcionellinae Wenz, 1938
  • Hampilinae Kobayashi, 1958
  • Securiconidae Missarzhevsky, 1989

Scenella is an extinct genus of fossil invertebrate animal which is generally considered to be a mollusc; at various times it has been suggested that this genus belongs with the gastropods, the monoplacophorans, or the helcionellids, although no firm association with any of these classes has been established.[4] An affinity with the hydrozoa (as a flotation device) has been considered,[1] although some authors oppose this hypothesis.[5] A gastropod affinity is defended on the basis of six pairs of internal muscle scars,[6] whilst the serially-repeated nature of these scars suggests to other authors a monoplacophoran affinity.[1] However the specimens showing this scarring have not been convincingly shown to belong to the genus Scenella.[1] A similarity to the Ediacaran Ovatoscutum has also been drawn.[7]

Description

The shell of Scenella is elongated along its anterior-posterior axis, and comprises concentric rings around a conical central peak. Radial and concentric corrugations exist in some species.[7] Some specimens are preserved as organic films, others appear to have been infilled with calcite.[1] They are usually preserved point-upwards, with their long axes consistently oriented; this probably represents their most stable position under their depositional current.[1] Soft parts have never been reported in association with Scenella, suggesting that the preserved fragments separated quickly from the associated tissue prior to burial.[1]

Fossil occurrence

Scenella lived from the Cambrian to the Ordovician. Its remains have been found in Antarctica, Asia, Europe, and North America. Individual fossils are common throughout the Burgess shale, where they often occur in dense aggregations.[1] Where they overlap, specimens deform as by draping.[1] Specimens are sometimes cracked or torn, with margins often damaged by folding or "tattering".[1] 1206 specimens of Scenella are known from the Greater Phyllopod bed, where they comprise 2.29% of the community.[8]

Taxonomy

Scenella from the Burgess Shale, Middle Cambrian, Walcott Quarry, near Field, British Columbia

Scenella is the only genus in the family Scenellidae. This family has no subfamilies and Scenella is the type genus of the family Scenellidae.

The taxonomy of the Gastropoda by Bouchet & Rocroi, 2005[3] categorizes Scenellidae in the superfamilia Scenelloidea within the Paleozoic molluscs of uncertain systematic position.

Species

Species in the genus Scenella include:[9]

Species Authority Range
Scenella affinis Ulrich and Schfield, 1897
Scenella amii (Matthew, 1902) Babcock and Robinson 1988 Burgess Shale (Mid Cambrian, 508 million years ago)[8]
Scenella anomala (Billings, 1865) Wagner 2008
Scenella augusta (Billings, 1865) Wagner 2008
Scenella barrandei (Linnarsson, 1879) (Bergerg-Madsen and Peel, 1986)[10]
Scenella beloitensis Ulrich and Scofield (1897)
Scenella clotho Walcott, 1936
Scenella compressa Ulrich and Scofield (1897)
Scenella conica Whiteaves, 1884
Scenella conula (Walcott, 1884)
Scenella conicum (Whitfield, 1886) Ulrich and Scofield (1897)
Scenella hujingtanensis Yu, 1979
Scenella magnifica Ulrich and Scofield (1897)
S.? mira Vasil’yeva, 1994
Scenella montrealensis Billings (1865)
Scenella obtusa (Sardeson, 1892) Ulrich and Scofield (1897)
Scenella orithyia (Billings, 1865) Ulrich and Scofield (1897)
Scenella pretensa Raymond, 1905
Scenella radialis Ulrich and Scofield (1897)
Scenella radians Babcock & Robinson
Scenella radiata Yu, 1979
Scenella reticulata (Billings, 1872) (type)[11]
Scenella retusa (Ford, 1873)[12]
Scenella unicarinata (Kobayashi, 1934) Wagner 2008
Scenella varians Walcott 1908
Scenella venillia (Billings, 1865) Wagner 2008
Scenella tenuistriata Chapman, 1911 Mid Cambrian[13]

References

  1. ^ a b c d e f g h i j Babcock, L. E.; Robison, R. A. (1988). "Taxonomy and paleobiology of some Middle Cambrian Scenella (Cnidaria) and Hyolithids (Mollusca) from western North America" (PDF). University of Kansas Paleontological Contributions. 121: 1–22. hdl:1808/3638.
  2. ^ Miller S. A. (after October 1889). North American geology and palaeontology: 389.
  3. ^ a b Bouchet P. & Rocroi J.-P. (Ed.); Frýda J., Hausdorf B., Ponder W., Valdés Á. & Warén A. 2005. Classification and nomenclator of gastropod families. Malacologia: International Journal of Malacology, 47(1-2). ConchBooks: Hackenheim, Germany. ISBN 3-925919-72-4. ISSN 0076-2997. 397 pp.
  4. ^ Yochelson, E. L.; Cid, D. G. L. (1984). "Reevaluation of the systematic position of Scenella". Lethaia. 17 (4): 331–340. doi:10.1111/j.1502-3931.1984.tb00679.x.[dead link‍]
  5. ^ Landing; Narbonne (1992). "Scenella and "A Chondrophorine (Medusoid Hydrozoan) from the Basal Cambrian (Placentian) of Newfoundland"". Journal of Paleontology. 66 (2): 338. Bibcode:1992JPal...66..338L. doi:10.1017/s0022336000033837. JSTOR 1305918. S2CID 132296800.
  6. ^ Rasetti (1954). "Internal Shell Structures in the Middle Cambrian Gastropod Scenella and the Problematic Genus Stenothecoides". Journal of Paleontology. 28 (1): 59–66. JSTOR 1300208.
  7. ^ a b Benjamin M. Waggoner; Allen G. Collins (March 1995). "A new chondrophorine (Cnidaria, Hydrozoa) from the Cadiz Formation (Middle Cambrian) of California". Paläontologische Zeitschrift. 69 (1–2): 7–17. Bibcode:1995PalZ...69....7W. doi:10.1007/BF02985970. ISSN 0031-0220. S2CID 128662109.
  8. ^ a b Caron, Jean-Bernard; Jackson, Donald A. (October 2006). "Taphonomy of the Greater Phyllopod Bed community, Burgess Shale". PALAIOS. 21 (5): 451–65. Bibcode:2006Palai..21..451C. doi:10.2110/palo.2003.P05-070R. JSTOR 20173022. S2CID 53646959.
  9. ^ Scenella. Paleobiology Database, accessed 16 August 2009.
  10. ^ BERGERG-MADSEN V, PEEL JS (1986). "Scenella barrandei (Mollusca) from the Middle Cambrian of Baltoscandia". Norsk Geologisk Tidsskrift. 66 (1): 81–86.
  11. ^ Billings (1872). "On some fossils from the primordial rocks of Newfoundland". Nat. Can. 2nd series. vi: 465–479.
  12. ^ Ford (1873). "On some new species of fossils from the Primordial or Potsdam group of Rensselaer County, New York (lower Potsdam)". American Journal of Science. 3. 5 (27): 211–215. Bibcode:1873AmJS....5..211F. doi:10.2475/ajs.s3-5.27.211. S2CID 130771815.
  13. ^ Chapman F. (1911). "New or Little Known Victorian Fossils in the National Museum". Proceedings of the Royal Society of Victoria, Melbourne 23: 305-324. plate 58-61.; Scenella tenuistriata at 313-314, plate LIX. figure 18 a,b.
Quelle: http://en.wikipedia.org/wiki/Metoptoma