Westonoceras
Encyclopedia
Westonoceras is an extinct nautiloid genus from the Discosorida
that lived during the Middle and Late Ordovician that has been found in North America, Greenland, and Northern Europe. It is the type genus for the Westonoceratidae
The siphuncle
is located close to the ventral wall. Segments are box-shaped and strongly expanded. Septal necks are strongly recumbent; connecting rings thick, with inflated bullettes. Parietal deposits grow forward from the septal foremina, commonly forming a continuous internal lining. Cameral deposits are common.
by loss of the initial endogastric curvature of the latter. It have rise to Winnipegoceras
in becoming more slender and compressed.
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...
that lived during the Middle and Late Ordovician that has been found in North America, Greenland, and Northern Europe. It is the type genus for the 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...
Description
The shell of Westonoceras forms a humped exogastric cyrtocone with its greatest height (gibbosity) at the anterior part of the mature phragrocone and posterior body chamber. The early juvenile portion is slender, gently exogastric or straight and rapidly increasing in size. Curvature increases during development. The dorsum, on the longitudinally concave side, is broadly rounded. The venter, on the longitudinally convex side, is narrow.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...
is located close to the ventral wall. Segments are box-shaped and strongly expanded. Septal necks are strongly recumbent; connecting rings thick, with inflated bullettes. Parietal deposits grow forward from the septal foremina, commonly forming a continuous internal lining. Cameral deposits are common.
Phylogeny
Westonoceras is derived from TeichertocerasTeichertoceras
Teichertoceras is a discosorid genus in the family Westonoceratidae characterized by an endogastric curvature to the early portion of the phragmocone....
by loss of the initial endogastric curvature of the latter. It have rise to 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...
in becoming more slender and compressed.
See also
- List of nautiloids
- Sepkoski, J.J. Jr. 2002. A compendium of fossil marine animal genera. D.J. Jablonski & M.L. Foote (eds.). Bulletins of American Paleontology 363: 1–560. Sepkoski's Online Genus Database (CEPHALOPODA)