Simardoceras
Encyclopedia
Simardoceras is a genus in the discosorid
(nautiloid cephalopod) family Westonoceratidae
from the Middle Ordovician of Quebec.
The shell of Simardoceras is a moderately expanding exogastric cyrtocone, said to resemble a rather large Oncoceras, but with a siphuncle that is definitely discosorid. The venter is almost uniformly convex in longitudinal profile. The dorsal profile changes from concave in the apical portion to straight, then slightly convex at the front of the phragmocone and back of the body chamber, the concave again near the aperture.
The siphuncle is ventral. Segments are subquadrate in outline and are longer than broad. Connecting rings are thick.
Although Simardoceras somewhat resembles Winnipegoceras
is the form of its siphuncle, it differs in its very broad cross section. The slender siphuncle segments also distinguish it from the apparently more closely related Sinclairoceras
and from its apparent derivative Reedsoceras
.
Sinclairoceras, Simardoceras, and Reedsoceras are found in beds of Black River age (Middle Ordovician) and seem to be closely related, and may even form a phylogenetic (evolutionary) series.
Discosorida
Discosorida is a unique order of cephalopods that lived from the beginning of the Middle Ordovician, through the Silurian, and into the Devonian. Discosorids are unique in the structure and formation of the siphuncle, the tube that runs through and connects the chambers in cephalopods, which unlike...
(nautiloid cephalopod) family Westonoceratidae
Westonoceratidae
Westonoceratidae are exogastric, mostly compressed, Discosorida of moderate size from the Middle Ordovician to the Lower Silurian.The siphuncle is typically close to the convexly curved outer margin of the phragmocone -the chambered part of the shell- taken to be ventral but may be more central in...
from the Middle Ordovician of Quebec.
The shell of Simardoceras is a moderately expanding exogastric cyrtocone, said to resemble a rather large Oncoceras, but with a siphuncle that is definitely discosorid. The venter is almost uniformly convex in longitudinal profile. The dorsal profile changes from concave in the apical portion to straight, then slightly convex at the front of the phragmocone and back of the body chamber, the concave again near the aperture.
The siphuncle is ventral. Segments are subquadrate in outline and are longer than broad. Connecting rings are thick.
Although Simardoceras somewhat resembles Winnipegoceras
Winnipegoceras
Winnipegoceras is an extinct nautiloid genus from the Ordovician belonging to the Order Discosorida.-Phylogeny:Winnipegoceras is included in the discosorid family Westonoceratidae and is derived from Westonoceras...
is the form of its siphuncle, it differs in its very broad cross section. The slender siphuncle segments also distinguish it from the apparently more closely related Sinclairoceras
Sinclairoceras
Sinclairoceras is a nautiloid cephalopod in the discosorid family Westonoceratidae from the Middle Ordovician Simard Limestone of Quebec. The shell is a compressed exogastric brevicone with venter narrowly and dorsum broadly rounded. The dorsum, at the upper surface, is only slightly concave...
and from its apparent derivative Reedsoceras
Reedsoceras
Reedsoceras is a large member of the discosorid family Westonoceratidae from the middle and upper Ordovician of North America....
.
Sinclairoceras, Simardoceras, and Reedsoceras are found in beds of Black River age (Middle Ordovician) and seem to be closely related, and may even form a phylogenetic (evolutionary) series.