Wutinoceras, orthoconic actinocerids

Actinocerida

The Actinocerida comprise an order of generally straight, medium to large cephalopods that lived during the early and middle Paleozoic, distinguished by a siphuncle composed of expanded segments that extend into the adjacent chambers, in which deposits formed within contain a system of radial...

 with ventral 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...

s composed of broadly expanded segments.and the type genus of the Wutinoceratidae

Wutinoceratidae

The Wutinoceratidae is a family of early actinocerids defined by Shimazu and Obata in 1938 for actinocerids with thick connecting rings and a complex irregular canal system...

. (Flower 1957, 1968)

Distinguishing Characters

Wutinoceras, as with its family the Wutinoceratidae, has a reticulate canal system within the siphuncle, distinguishing it from later forms with arcuate canal systems. Septal necks are cyrtochoanitic (outwardly curved) and may be recumbent. Connecting rings are thick, reflective of the ancestral form.

Varieties

There are three varieties of Wutinoceras, based on the form of the siphuncle and each containing a number of species. These have not be ascribed to subgenera. There are those with broad segments and strongly recumbent brims to the septal necks; those with large segments and rings free ventrally; and those with small segments in which the brims on the dorsal side are sometimes free. The genotype Wutinoceras foerste, which comes from northeast China (Manchuria

Manchuria

Manchuria is a historical name given to a large geographic region in northeast Asia. Depending on the definition of its extent, Manchuria usually falls entirely within the People's Republic of China, or is sometimes divided between China and Russia. The region is commonly referred to as Northeast...

) is of the second variety.

Distribution

Wutinoceras of the broad segment variety are found in Newfoundland, Oklahoma, and Tasmania; of the large segment variety in Utah, Nevada, Newfoundland, and Manchuria. Those of the small segment variety have only been found in Nevada. (Flower 1968) unless new species described in Flower 1976 from elsewhere can be included.

Phylogeny

Wutinoceras may have its origin in the primitive actinoceroid Georgina from the upper Lower Ordovician of Northern Australia

Australia

Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

 and east Asia (Wade 1988) although its exact ancestor remains elusive. Wutinoceras was once thought to be derived from Polydesmia

Polydesmia

Polydesmia is a genus of fungi within the Hyaloscyphaceae family. The genus contains 7 species.-External links:* at Index Fungorum...

from northern China, which was later) found to come from beds that overly those with Wutinoceras, thereby precluding the possibility.

Wutinoceras gave rise to Cyrtonybyoceras with the development of a curved, cyrtoconic shell and to Adamsoceras

Adamsoceras

Adamsoceras is an actinocerid of the family Wutinoceratidae, with spheroidal siphuncle segments like Ormoceras but having a reticular canal system like Wutinoceras. Adamsoceras has a slender, gently expanding, orthoconic shell that is slightly broader than high, i.e...

with the development of a more narrow siphuncle. Wutinoceras is also the ancestor of the Armenoceratidae

Armenoceratidae

Armenoceratidae is a family of early Paleozoic nautiloid cephalopods belonging to the Order Actinocerida.The Armenoceratidae, established by Troedsson is characterized by large, straight or slightly curved shells and large siphuncles with strongly expanded segments between the septa. Septal necks...

 which gave rise in the later Middle Ordovician to Actinoceras

Actinoceras

Actinoceras is the principal and root genus of the Actinoceratidae, a major family in the Actinocerida, that lived during the Middle and Late Ordovician.- Morphology:...

and Gonioceras

Gonioceras

Gonioceras is an actinocerid with a broad, low shell; flattened ventrally, convexly rounded dorsally; top and bottom meeting at an acute angle along the sides. In most the shell is rather thin, especially along the lateral portion. The aperture is contracted...