Plectronoceras
Encyclopedia
Plectronoceras is the earliest known shelly cephalopod
, dating to the Upper Cambrian.
Its 14 known specimens hail from the basal Fengshan Formation (north-east China) of the earliest Fengshanian stage. None of the fossils are complete, and none show the tip or opening of the shell. Approximately half of its shell was filled with septa; 7 were recorded in a 2 cm shell. Its shell contains transverse septa separated by about half a millimetre, with a siphuncle
on its concave side. Its morphology matches closely to that hypothesised for the last common ancestor of all cephalopods.
Plectronoceras is the type genus of the family Plectronoceratidae.
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
, dating to the Upper Cambrian.
Its 14 known specimens hail from the basal Fengshan Formation (north-east China) of the earliest Fengshanian stage. None of the fossils are complete, and none show the tip or opening of the shell. Approximately half of its shell was filled with septa; 7 were recorded in a 2 cm shell. Its shell contains transverse septa separated by about half a millimetre, with a siphuncle
Siphuncle
The siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod mollusk. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the living nautiluses, cuttlefish, and Spirula...
on its concave side. Its morphology matches closely to that hypothesised for the last common ancestor of all cephalopods.
Plectronoceras is the type genus of the family Plectronoceratidae.