Carbactinoceras

Carbactinoceras is a genus of Early Carboniferas (Visean) actincoceroids first found in Europe (Germany) related to Rayonnoceras but probably smaller.

Description

Carbactinoceras shells are straight and generally unknown beyond the early growth stage. The siphuncle is large, central to subcentral; segments inflated, septal necks cyrochoantiic and recumbent. The endosiphuncular canal system observed is well developed with thin radial canals perpendicular to the central canal, and leading to a narrow seam along the connecting rings called a perispatium.

Taxonomic position

Although Carbactinoceras had been considered an actinocerid according to the American Teatise Part K, 1964, based on the internal characters of the siphuncle, the initial chambers of the phragmocone indicate that this genus is an actinoceroid homeomorph (lookalike) belonging phylogenetically to the Pseudorthocerida

References

• Bjorn Kroger 2007. Carboniferous Actinoceratoid Nautiloidea (Cephalopoda) - a new perspective) . Journal of Paleontology, July 2007
• Curt Teichert, 1964. Actinoceratoidea. Treatise on Invertebrate Paleontology, Part K. Geological Society of America and University of Kansas Press.
• Carbactinoceras Paleobiology Database
• J.J. Sepkoski 2002. List of Cephalopod genera.

Notable fossil cephalopods (listed by first occurrence)
Cenozoic	The belemnite-cuttlefish-like Belosaepia	Evolutionary history of cephalopods
Mesozoic	Advanced nautiloids Nautilaceae True ammonites Early coleoids Proteroctopus Styletoctopus Keuppia Palaeoctopus Paleocirroteuthis Ceratitid ammonoids late Nautilida Advanced belemnoids Diplobelids: Diplobelus Belemnites: Belemnites Belemnopsis Belemnotheutis
Palaeozoic	First appearance of long-lasting lineages Goniatite and ceratite ammonoids Probable coleoid ancestor Bactritida Earliest belemnoids: Aulacocerids: Aulacoceras Phragmoteuthids: Phragmoteuthis Early forms the earliest cephalopod group Ellesmerocerida Orthocones: Endocerida, Orthocerida, Actinocerida Brevicones: Ascocerida, Oncocerida Earliest coiled cephalopods: Tarphycerida Spirulid?: Shimanskya Octopus Pohlsepia
Cambrian	Earliest unambiguous cephalopods: Plectronocerida Plectronoceras Monoplacophoran-like ancestral forms: Knightoconus Possible, nude, "stem-group cephalopods": Nectocarididae