Plectronoceras

Plectronoceras Temporal range: Upper Cambrian PreЄ Є O S D C P T J K Pg N
Plectronoceras cambria
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Cephalopoda
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] [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" (PDF). Acta Palaeontologica Polonica. 26 (2): 161–191.
2. 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.