Plectronoceras is the earliest known shelled cephalopod, dating to the Late Cambrian.[1][2][3] None of the fossils are complete, and none show the apex or aperture of the shell.[3] Approximately half of its shell was filled with septa; 7 were recorded in a 2 centimetres (0.79 in) shell.[4] Its shell contains transverse septa separated by about half a millimetre, with a siphuncle on its concave side.[3] Its morphology matches closely to that hypothesised for the last common ancestor of all cephalopods.[3]

Plectronoceras
Temporal range: Late Cambrian
~501–488.3 Ma
Life reconstruction of P. cambria
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Subclass: Nautiloidea
Order: Plectronocerida
Family: Plectronoceridae
Genus: Plectronoceras
Ulrich & Foerste, 1933
Species
  • P. cambria Walcott, 1905
  • P. exile Flower, 1964
  • P. gracile Flower, 1964
  • P. huaibeiense Chen & Qi, 1979
  • P. liaotungense Kobayashi, 1935

Plectronoceras is the type genus of the family Plectronoceratidae. Fossils of Plectronoceras have been found in the San Saba Limestone of Texas.[2]

References

edit
  1. ^ Dzik, J. (1981). "Origin of the cephalopoda" (PDF). Acta Palaeontologica Polonica. 26 (2): 161–191.
  2. ^ a b Plectronoceras at Fossilworks.org
  3. ^ a b c d Clarke, M.R. (1985), "Main features of cephalopod evolution", in Wilbur, Karl M.; Clarke, M.R.; Trueman, E.R. (eds.), The Mollusca, vol. 12. Paleontology and neontology of Cephalopods, New York: Academic Press, ISBN 0-12-728702-7
  4. ^ Webers, G. F.; Yochelson, E. L. (1989). "Late Cambrian molluscan faunas and the origin of the Cephalopoda". In Crame, J. A. (ed.). Origins and Evolution of the Antarctic Biota. Vol. 47. pp. 29–42. doi:10.1144/GSL.SP.1989.047.01.04. {{cite book}}: |journal= ignored (help)