Wutinoceras

Wutinoceras is a genus of now extinct nautiloid cephalopod of the Wutinoceratidae family. It exhibits orthoconic actinocerids with ventral siphuncles composed of broadly expanded segments (Flower 1957,^[1] 1968^[2])

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, components of the siphuncle that project from the back side of the septa, 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.^[2] The genotype Wutinoceras foerste, which comes from northeast China (Manchuria) 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)^[2] unless new species described in Flower 1976^[3] from elsewhere can be included.

Phylogeny

Wutinoceras may have its origin in the primitive actinoceroid Georgina from the upper Lower Ordovician of Northern Australia and east Asia (Wade 1988)^[4] although its exact ancestor remains elusive. Wutinoceras was once thought to be derived from Polydesmia^[1] from northern China, which was later)^[3] 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 with the development of a more narrow siphuncle.^[1][2] Wutinoceras is also the ancestor of the Armenoceratidae which gave rise in the later Middle Ordovician to Actinoceras and Gonioceras

References