Plectronoceras

Plectronoceras; Temporal range: Cambrian; 501–488.3 Ma PreꞒ Ꞓ O S D C P T J K Pg N
	Life restoration
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Cephalopoda
Subclass:	Nautiloidea
Order:	†Plectronocerida
Family:	†Plectronoceridae
Genus:	†Plectronoceras; Ulrich & Foerste, 1933
Species
	†Plectronoceras cambria; Walcott, 1905;

Plectronoceras is an extinct genus of early shelled cephalopod, dating to the Late Cambrian. None of the fossils are complete, and none show the apex or aperture of the shell. Around half of its shell was filled with septa; 7 were recorded in a 2 centimetres (0.79 in) shell. Its shell contains transverse septa separated by about half a millimetre, with a siphuncle on its concave side. It is among the oldest known shelled cephalopods (the Early Cambrian Eoceras being older), and its morphology matches closely that hypothesised for the last common ancestor of all cephalopods.

Plectronoceras is the type genus of the family Plectronoceratidae. Fossils of Plectronoceras have been found in the San Saba Limestone of Texas, United States and in Yunnan, China.

Several species have been included in the genus Plectronoceras, though a 2024 review reorganized their taxonomy; P. exile and P. gracile were synonymyzed with Palaeoceras mutabile, while P. huaibeiense and P. liaotungense were synonymyzed with P. cambria, the type species of Plectronoceras.

References

↑ Dzik, J. (1981). "Origin of the cephalopoda" (PDF). Acta Palaeontologica Polonica. 26 (2): 161–191.
1 2 Plectronoceras at Fossilworks.org
1 2 3 4 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.
↑ Song, Zuchen; Pan, Bing; Guo, Junfeng; Vinther, Jakob; Li, Guoxiang; Han, Jian; Van Iten, Heyo; Zhao, Xiaofang; Pei, Xianzhi; Peng, Jiaxin; Qiang, Yaqin; Zhang, Boyao; Wen, Hanjie (2026-07-31). "Earliest siphuncle-bearing cephalopod from the early Cambrian". Nature. doi:10.1038/s41586-026-10868-y. ISSN 0028-0836. PMID 42527604.
↑ Pohle, Alexander; Jell, Peter; Klug, Christian (2024-02-29). "Plectronoceratids (Cephalopoda) from the latest Cambrian at Black Mountain, Queensland, reveal complex three-dimensional siphuncle morphology, with major taxonomic implications". PeerJ. 12 e17003. Bibcode:2024PeerJ..1217003P. doi:10.7717/peerj.17003. ISSN 2167-8359. PMC 10909373. PMID 38436030.

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

[FWPlectronoceras-2] 1 2 Plectronoceras at Fossilworks.org

[mollusca12-2-3] 1 2 3 4 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.

[Eoceras-5] Song, Zuchen; Pan, Bing; Guo, Junfeng; Vinther, Jakob; Li, Guoxiang; Han, Jian; Van Iten, Heyo; Zhao, Xiaofang; Pei, Xianzhi; Peng, Jiaxin; Qiang, Yaqin; Zhang, Boyao; Wen, Hanjie (2026-07-31). "Earliest siphuncle-bearing cephalopod from the early Cambrian". Nature. doi:10.1038/s41586-026-10868-y. ISSN 0028-0836. PMID 42527604.

[Pohle2024-6] Pohle, Alexander; Jell, Peter; Klug, Christian (2024-02-29). "Plectronoceratids (Cephalopoda) from the latest Cambrian at Black Mountain, Queensland, reveal complex three-dimensional siphuncle morphology, with major taxonomic implications". PeerJ. 12 e17003. Bibcode:2024PeerJ..1217003P. doi:10.7717/peerj.17003. ISSN 2167-8359. PMC 10909373. PMID 38436030.