''Plectronoceras'' is the earliest known shelled
cephalopod
A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head ...
, dating to the Late Cambrian.
[''Plectronoceras'']
at Fossilworks
Fossilworks is a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database
The Paleobiology Database is an online resource for information on the distribution and classification of fossil animals ...
.org None of the fossils are complete, and none show the apex or aperture of the shell.
[ Approximately half of its shell was filled with septa; 7 were recorded in a shell.]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 ...
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. Fossils of ''Plectronoceras'' have been found in the San Saba Limestone of Texas.][
]
References
Prehistoric nautiloid genera
Cambrian molluscs
Cambrian animals of North America
Cambrian United States
Fossil taxa described in 1933
{{paleo-Nautiloidea-stub
Cambrian genus extinctions