Oxygonioceras
Encyclopedia
Oxygonioceras is a genus in the Oncocerid
family, Brevicoceratidae
, from the Middle Silurian
of North America and Europe.
Oxygonioceras, named by Foeste, 1925, has a loosely coiled, dextrally torticonic shell with a rounded dorsum on the inside of the spiral and an angular or subangular venter on the outside; suture with broad lateral lobes and ventral siphuncle with expanded, nummuloidal segments.
Although also torticonically gyroconic -- having an out of plane open spiral - Oxygonioceras differs from Naedyceras
and closely related genera in that the siphuncle
segments are empty, rather than being actinosiphonate.
Oncocerida
The Oncocerida comprise a diverse group of generally small nautiloid cephalopods known from the Middle Ordovician to the Mississippian ,in which the connecting rings are thin and siphuncle segments are variably expanded...
family, Brevicoceratidae
Brevicoceratidae
The Brevicoceratidae, named by Flower in 1941, is a family of oncocerids that contains genera characterized by exogastric gyrocones, brevicones, and torticones that tend to develop vestigial actinosiphonate deposits and subtriangular transverse sections...
, from the Middle Silurian
Silurian
The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...
of North America and Europe.
Oxygonioceras, named by Foeste, 1925, has a loosely coiled, dextrally torticonic shell with a rounded dorsum on the inside of the spiral and an angular or subangular venter on the outside; suture with broad lateral lobes and ventral siphuncle with expanded, nummuloidal segments.
Although also torticonically gyroconic -- having an out of plane open spiral - Oxygonioceras differs from Naedyceras
Naedyceras Group
The Naedyceras group is made up of three similar and closely related genera, Naedyceras, Gonionaedyceras, and Gyronaedyceras; three gyroconic members of the Brevicoceratidae, within the nautiloid order Oncocerida....
and closely related genera in that the 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...
segments are empty, rather than being actinosiphonate.
References
- Sweet. W. C. 1964. Nautiloidea-Oncocerida; Treatise on Invertebrate Paleontology, Part K. Geol Soc of America and Univ Kansas press, R.C. Moore (Ed)