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Temporal range: Upper Cambrian
File:Plectronoceras cambria.jpg
P. cambria
Scientific classification e
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Order: Plectronocerida
Family: Plectronoceridae
Genus: Plectronoceras
Ulrich & Foerste, 1933
  • P. cambria Walcott, 1905
  • P. exile Flower, 1964[verification needed]
  • P. gracile Flower, 1964
  • P. liaotungense Kobayashi, 1935

Plectronoceras is the earliest known shelly cephalopod, dating to the Upper Cambrian.[1] [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.


  1. Dzik, J. (1981). "Origin of the cephalopoda" (PDF). Acta Palaeontologica Polonica. 26 (2): 161–191. 
  2. 2.0 2.1 2.2 2.3 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. p. 29. doi:10.1144/GSL.SP.1989.047.01.04.