Plectronoceras

Plectronoceras
Temporal range: Upper Cambrian
Scientific classification
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. liaotungense Kobayashi, 1935

Plectronoceras is the earliest known shelly cephalopod, dating to the Upper Cambrian.[1] Its 14 known specimens hail from the basal Fengshan Formation (north-east China) of the earliest Fengshanian stage.[2] None of the fossils are complete, and none show the tip or opening of the shell.[2] Approximately half of its shell was filled with septa; 7 were recorded in a 2 cm shell.[3] Its shell contains transverse septa separated by about half a millimetre, with a siphuncle on its concave side.[2] Its morphology matches closely to that hypothesised for the last common ancestor of all cephalopods.[2]

Plectronoceras is the type genus of the family Plectronoceratidae.

References

  1. ^ Dzik, J. (1981). "Origin of the cephalopoda". Acta Palaeontologica Polonica 26 (2): 161–191. http://www.paleo.pan.pl/people/Dzik/Publications/Cephalopoda.pdf. 
  2. ^ a b c d Clarke, M.R.; Trueman, E.R. (1985), "Main features of cephalopod evolution", in Wilbur, Karl M.; Clarke, M.R.; Trueman, E.R., The Mollusca, 12. Paleontology and neontology of Cephalopods, New York: Academic Press, ISBN 0-12-728702-7 
  3. ^ Webers, G. F.; Yochelson, E. L. (1989). "Late Cambrian molluscan faunas and the origin of the Cephalopoda". In Crame, J. A.. Origins and Evolution of the Antarctic Biota. 47. Geological Society, London: Special Publications. pp. 29. doi:10.1144/GSL.SP.1989.047.01.04.  edit