Plectronoceras

Plectronoceras is the earliest known shelled cephalopod, 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 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
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 type genus of the family Plectronoceratidae. Fossils of Plectronoceras have been found in the San Saba Limestone of Texas and the Yunnan Province of China.^[2]