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Plectronoceras is the earliest known shelly cephalopod, dating to the Late Cambrian.[1][2][3] None of the fossils are complete, and none show the tip or opening 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]

Temporal range: Late Cambrian
~501–488.3 Ma
Plectronoceras cambria.jpg
Plectronoceras cambria
Scientific classification e
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Subclass: Nautiloidea
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 type genus of the family Plectronoceratidae. Fossils of Plectronoceras have been found in the San Saba Limestone of Texas.[2]


  1. ^ Dzik, J. (1981). "Origin of the cephalopoda" (PDF). Acta Palaeontologica Polonica. 26 (2): 161–191.
  2. ^ a b Plectronoceras at
  3. ^ 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. (eds.), The Mollusca, 12. Paleontology and neontology of Cephalopods, New York: Academic Press, ISBN 0-12-728702-7CS1 maint: multiple names: authors list (link)
  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. 47. Geological Society, London: Special Publications. p. 29. doi:10.1144/GSL.SP.1989.047.01.04.