Plectronoceras

Plectronoceras; Temporal range: Late Cambrian; ~501–488.3 Ma PreꞒ Ꞓ O S D C P T J K Pg N
	Life reconstruction of P. cambria
Scientific 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 earliest known cephalopod with a shell, 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 is the type genus of the family Plectronoceratidae. Fossils of Plectronoceras have been found in the San Saba Limestone of Texas.^[2]

References

^ Dzik, J. (1981). "Origin of the cephalopoda" (PDF). Acta Palaeontologica Polonica. 26 (2): 161–191.
^ ^a ^b Plectronoceras at Fossilworks.org
^ ^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
^ Webers, G. F.; Yochelson, E. L. (1989). Crame, J. A. (ed.). "Late Cambrian molluscan faunas and the origin of the Cephalopoda". Geological Society, London, Special Publications. 47 (1): 29–42. Bibcode:1989GSLSP..47...29W. doi:10.1144/GSL.SP.1989.047.01.04.

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[Dzik1981-1] Dzik, J. (1981). "Origin of the cephalopoda" (PDF). Acta Palaeontologica Polonica. 26 (2): 161–191.

[FWPlectronoceras-2] Plectronoceras at Fossilworks.org

[mollusca12-2-3] 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

[Webers1989-4] Webers, G. F.; Yochelson, E. L. (1989). Crame, J. A. (ed.). "Late Cambrian molluscan faunas and the origin of the Cephalopoda". Geological Society, London, Special Publications. 47 (1): 29–42. Bibcode:1989GSLSP..47...29W. doi:10.1144/GSL.SP.1989.047.01.04.

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