Slender Oncoceratidae

Last updated

Slender Oncoceratidae
Temporal range: M Ord- U Sil
Oocerina plebeia.JPG
Oonocerina plebeia, Barrande from Slivenec, Prague, (Czech Republic) at the National Museum (Prague)
Scientific classification
Kingdom:
Animalia
Phylum:
Mollusca
Class:
Cephalopoda
Subclass:
Nautiloidea
Order:
Oncocerida
Family:
Oncoceratidae

Hyatt, 1884
Genera

See text

Slender Oncoceratidae are those in the family Oncoceratidae, (Nautiloidea, Oncocerida) which have slender, commonly curved, shells. Some like Oocerina are gently curved, almost straight, and with only slight expansion. Others like Dunleithoceras are strongly curved with a more notable rate of expansion. Inclusion in this somewhat arbitrary category is based on illustrations in the Treatise Part K, 1964.

Contents

Included genera

Loganoceras and Romingoceras from the Middle Ordovician of North America have strongly curved shells. Loganoceras, named by Foerste in 1921, (K284) has a circular cross section and an empty siphuncle ventral of the center. The genotype, L. regulare, comes from Ontario. Romingoceras, also named by Foerste in 1932, differs in having a depressed, ovoid, cross section. Romingoceras expands slowly and like Loganoceras is strongly curved, may even be gyroconic (openly coiled). The ventral siphuncle is small, with oblong segments. The genotype, R. josephianum also comes from Ontario.

Also from the Middle Ordovician of North America is the long, slightly curved Ehlersoceras (K284), named by Foerste, 1932. Ehlersoceras has a small subventral siphuncle, depressed cross section and almost no expansion. As with Longanoceras and Romingoceras, the genotype of Ehlersoceras, E. huronense comes from Ontario. Ehlersoceras differs from Longanoceras and Romingoceras in having a much gentler exogastric curvature.

Richardsonoceras (K288), named also by Foerste in 1932, and Dunleithoceras (K284), named by him in 1924, come from both the Middle and Upper Ordovician of North America. Both are strongly curved with a notable rate of expansion; ventral sides, as with the previous genera, are on the outside, convex curvature, making them, again, exogastric.

Dunleithoceras has a subcircular cross sections with a rounded longitudinal ridge on the venter. Richardsonoceras, has a sharply rounded, keel-like, venter. Richardsonoceras is less rapidly expanding and not as strongly curved as Dunleithoceras. The genotype of Dunleithoceras, D. dunleithense, comes from the Middle Ordovician of Illinois, that of Richardsonoceras, R. simplex, is from the Middle Ordovician of Ontario.

Oonoceras (K288), from the Middle Ordovician to Middle Silurian of Europe and North America named by Hyatt in 1884, has a slender compressed exogastrically curved shell with a gradual expansion. The genotype, O. acinaces, is from Middle Silurian of central Europe. The sutures in Oonoceras form lateral lobes. The camerae (chambers) and body chamber are short. The siphuncle, which is close to the venter, is cyrtochoanitic, empty, with expanded segments. Oocerina (K288), named by Foerste, 1926, is a slender, exogastric genus, like Oonoceras, from the Upper Silurian of Europe, Russia and possibly North America. Oocerina differs primarily in having an actinosiphonate siphuncle composed of numuloidal (beaded) segments. Paroocerina (K288), named by Zhurevleva in 1961, is a slender oncoceratid from the Middle and Upper Silurian of eastern Europe and ex-USSR (Russia), similar to Oocerina, but with a hyponomic sinus. The genotypes of Oocerina and Paroocerina, respectively O.lentigratum and P. podolskensis, are from the Upper Silurian of central Europe and Russia

Relationships

A close relationship can be inferred between Loganoceras and Romingoceras and between Dunleithoceras and Richardsonoceras from the Middle and Upper Ordovician of North America as they are respectively from the same area from the same time. Ehlersoceras seems to stand more alone. A close relationship may also be inferred between the primarily Silurian genera from Europe, including Russia; Oonoceras, Oocerina and Paroocerina, which are very similar in overall form.

The slender type oncoceratids give way to the strongly compressed Digenuoceras with sharply acute dorsum and venter, and to the more conical Miamiceras and Rizoceras .

Related Research Articles

<span class="mw-page-title-main">Oncocerida</span> Extinct order of nautiloids

The Oncocerida comprise a diverse group of generally small nautiloid cephalopods known from the Middle Ordovician to the Mississippian, in which the connecting rings are thin and siphuncle segments are variably expanded. At present the order consists of some 16 families, a few of which, such as the Oncoceratidae, Brevicoceratidae, and Acleistoceratidae contain a fair number of genera each while others like the Trimeroceratidae and Archiacoceratidae are represented by only two or three.

The Lowoceratidae is a small family of discosorids, early nautiloid cephalopods, from the Middle Silurian in which the characteristic bullette is found only in early growth stages. Lowoceratids were first found in Southampton Island in the Canadian arctic.

<span class="mw-page-title-main">Acleistoceratidae</span> Extinct family of molluscs

The Acleistoceratidae is a family of oncocerids that contains genera characterized by depressed exogastric brevicones and cyrtocones that range from the Middle Silurian to the Middle Devonian. The siphuncle is broadly expanded, and in some actinosiphonate.

Osbornoceras is a genus of Lower Silurian cyrtoconic nautiloid cephalopods known from Ohio and possibly Manitoba, one of five general currently included in the oncocerid family Karoceratidae.

Winnipegoceras is an extinct nautiloid genus from the Ordovician belonging to the Order Discosorida.

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 Graciloceratidae is a family of nautiloid cephalopods from the Middle and Upper Ordovician belonging to the Oncocerida, characterized by exogastric cyrtocones that expand slightly or moderately and have thin walled, orthochoanitic marginal or subventral, tubular siphuncles.

<span class="mw-page-title-main">Oncoceratidae</span> Extinct family of nautiloids

Oncoceratidae is a family of nauatiloid cephalopods in the order Oncocerida established by Hyatt, 1884, that range from the Middle Ordovician to the Upper Silurian.

The Tripteroceratidae is a family of depressed, straight to slightly curved nautiloid cephalopods from the middle and upper Ordovician with generally flattened venters and empty siphuncles with straight to inflated segments included in the Oncocerida.

<span class="mw-page-title-main">Phragmoceratidae</span> Extinct family of molluscs

The Phragmoceratidae is a family of extinct nautiloid cephalopods from the Order Discosorida that lived during the latter part of the Silurian.

<span class="mw-page-title-main">Armenoceratidae</span> Extinct family of molluscs

The Armenoceratidae are a family of early Paleozoic nautiloid cephalopods belonging to the order Actinocerida.

Oonoceras is an extinct genus of fossil cephalopods included in the nautiloid order Oncocerida and the family Oncoceratidae from the Middle Ordovician to Middle Silurian of North America and Europe, arbitrarily included in the Slender Oncoceratidae.

Pentameroceras is a straight to slightly exogastric breviconic oncocerid from the middle Silurian of North America and Europe belonging to the Trimeroceratidae.


Blakeoceras is a nautiloid cephalopod from the Oncocerida family Nothoceratidae with a curved shell that lived in shallow seas from the Silurian to the Middle Devonian in what has become Europe.

<i>Oocerina</i>

Oocerina is an extinct genus of nautiloid cephalopods that lived during the Late Silurian of Europe, Russia, and North America.

Minganoceras is a genus in the oncocerid family, Valcouroceratidae, named by Foeste, 1938, from the Middle Ordovician of Quebec, found on Mingan Island.

Augustoceras is a genus of nautiloid cephalopods included in the order Oncocerida and family Valcouroceratidae. It is known form the Middle and Upper Ordovician of Kentucky and Ohio in the US.

Galtoceras is a cyrtoconic nautiloid from the Middle Silurian of North America, named by Foerste in 1934.

Kentlandoceras is a genus of middle Ordovician Oncocerids. Its shell is curved exogastrically, such that the ventral margin is longitudinally convex, but less so than in Loganoceras, and with a submarginal ventral siphuncle instead. The siphuncle in Loganoceras is subcentral. The related Romingoceras is more curved, also with a ventral siphuncle.

Maelonoceras is a Late Ordovician - early Silurian oncocerid found in Ontario.

References

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.