Brevicoceras
Encyclopedia
Brevicoceras is an extinct prehistoric nautiloid genus from the order Oncocerida with wide distribution in the Middle Devonian
in Eastern North America, Russia and Morocco. Nautiloids form a broad group of shelled cephalopods that were once diverse and numerous but are now represented by only a handful of species in two genera.
close to the ventral margin. The siphuncular or ventral side has a convex profile while the dorsal side opposite has a concave profile over the more juvenile or apical part of the chambered phragomocone and becomes convex over the latter part and living chamber. The shell is slightly broader than high in section. The dorsal or antisiphuncular side is flattened , while the ventral or siphuncular side is more narrowly rounded The septa are shallow and evenly curved ; sutures are with broad shallow dorsal and ventral lobes that diverge to the rear and lateral saddles that extend forward. The ventral siphuncle is slender with short expanded segments that give it a nummuloidal or beaded appearance, and irregular actinosiphonate deposits The widest part of the shell is near the front of the phragmocone or rear of the living chamber. From there it narrows somewhat toward the aperture
which is transverse and slightly contracted. The rim or peristome has a mid dorsal and pair of ventral lateral salients and a narrow mid ventral hyponomic sinus confirming the siphuncle is ventral.
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
in Eastern North America, Russia and Morocco. Nautiloids form a broad group of shelled cephalopods that were once diverse and numerous but are now represented by only a handful of species in two genera.
Taxonomy
Brevicoceras was named by Flower(1938) and is type genus for the Brevicoceratidae, a family established in the Oncocerida by Flower in 1941Morphology
Brevicoceras produced short, breviconic, shells; with an exogastric aspect and siphuncleSiphuncle
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...
close to the ventral margin. The siphuncular or ventral side has a convex profile while the dorsal side opposite has a concave profile over the more juvenile or apical part of the chambered phragomocone and becomes convex over the latter part and living chamber. The shell is slightly broader than high in section. The dorsal or antisiphuncular side is flattened , while the ventral or siphuncular side is more narrowly rounded The septa are shallow and evenly curved ; sutures are with broad shallow dorsal and ventral lobes that diverge to the rear and lateral saddles that extend forward. The ventral siphuncle is slender with short expanded segments that give it a nummuloidal or beaded appearance, and irregular actinosiphonate deposits The widest part of the shell is near the front of the phragmocone or rear of the living chamber. From there it narrows somewhat toward the aperture
Aperture (mollusc)
The aperture is an opening in certain kinds of mollusc shells: it is the main opening of the shell, where part of the body of the animal emerges for locomotion, feeding, etc....
which is transverse and slightly contracted. The rim or peristome has a mid dorsal and pair of ventral lateral salients and a narrow mid ventral hyponomic sinus confirming the siphuncle is ventral.