Nautiloids are a group of marine cephalopods (Mollusca) which originated in the Late Cambrian and are represented today by the living Nautilus and Allonautilus. Fossil nautiloids are diverse and speciose, with over 2,500 recorded species. They flourished during the early Paleozoic era, when they constituted the main predatory animals. Early in their evolution, nautiloids developed an extraordinary diversity of shell shapes, including coiled morphologies and giant straight-shelled forms (orthocones). Only a handful of rare coiled species, the nautiluses, survive to the present day.
Discosorida are an 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 camerae (chambers) in cephalopods, which unlike those in other orders is zoned longitudinally along the segments rather than laterally. Siphuncle structure indicated that the Discosorida evolved directly from the Plectronoceratida rather than through the more developed Ellesmerocerida, as did the other orders. Finally and most diagnostic, discosorids developed a reinforcing, grommet-like structure in the septal opening of the siphuncle known as the bullette, formed by a thickening of the connecting ring as it draped around the folded back septal neck.
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.
Franklinoceras is an extinct gensu of cephalopods from the nautiloid order, Discosorida. Nautiloids comprise a subclass of shelled cephalopods that were once diverse and numerous but are now represented by only a handful of species.
Kionoceras is an extinct nautiloid cephalopod genus included in the orthocerid family Kionoceratidae with scattered worldwide distribution from the Middle Ordovician to the Lower Permian. Kionoceratids are orthocerids with prominent longitudinal ornamentation on their shells, sometimes augmented by secondary transverse ornamentation. Orthocerids are, of course, prehistoric nautiloides with generally straight and elongate shells, mostly with central or subcentral siphuncles.
Hoeloceras is an extinct orthoconic nautiloid cephalopod from the upper Ordovician, generally included in the Actinocerida. Nautiloids are a subclass of shelled cephalopods that were once diverse and numerous but are now represented by only a couple of genera, Nautilus and Allonautilus.
Winnipegoceras is an extinct nautiloid genus from the Ordovician belonging to the Order Discosorida.
Ulrichoceras is recognised as the basal cyrtogomphoceratid genus, which is the source for the rest of the Cyrtogomphoceratidae as well as for the Westonoceratidae. The Cyrtogomphoceratidae are endogastric, the Westonoceratidae, exogastric.
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
Donacoceras is an extinct genus of actively mobile carnivorous cephalopod, essentially a Nautiloid that lived in what would be North America during the Ordovician from 460.5—443.7 mya, existing for approximately 16.8 million years.
Hemicosmorthoceras is an extinct genus of actively mobile carnivorous cephalopod, essentially a Nautiloid, that lived in what would be present day Europe during the Silurian to Devonian from 422.9—412.3 mya, existing for approximately 10.6 million years.
Hemiphragmoceratidae is a family of endogastrically brevconic oncocerids characterized by elaborately visored apertures in which the hyponomic sinus in mature specimens is on a spout-like process and there may be lateral and dorsal salients.. Shells are compressed with the apical portion curved and the anterior straight. Siphucles are nummuloideal with expanded spheroidal segments and continuously actinosiphonate interiors.
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.
The Phragmoceratidae is a family of extinct nautiloid cephalopods from the Order Discosorida that lived during the latter part of the Silurian.
Mandaloceratidae is a family in the nautiloid cephalopod order Discosorida, from the Middle and Upper(?) Silurian characterized by short, essentially straight shells referred to as breviconic, typically with a faintly exogastric shape produced by the profile of the body chamber.
Sinclairoceras is a nautiloid cephalopod in the discosorid family Westonoceratidae from the Middle Ordovician Simard Limestone of Quebec. The shell is laterally compressed, upwardly curved, and short; an exogastric brevicone with the venter narrowly and dorsum broadly rounded. The dorsum, at the upper surface, is only slightly concave longitudinally. The venter, at the lower surface, is more strongly convex longitudinally, drawing away from the dorsum and forming a hump at the anterior end of the phragmocone where Sinclairoceras reaches its greatest width.
Paleontology in Wisconsin refers to paleontological research occurring within or conducted by people from the U.S. state of Wisconsin. The state has fossils from the Precambrian, much of the Paleozoic, and the later part of the Cenozoic. Most of the Paleozoic rocks are marine in origin. Because of the thick blanket of Pleistocene glacial sediment that covers the rock strata in most of the state, Wisconsin’s fossil record is relatively sparse. In spite of this, certain Wisconsin paleontological occurrences provide exceptional insights concerning the history and diversity of life on Earth.
Cyrtogomphoceras is a genus of nautiloid cephalopods, recognized by its large breviconic shell with a notable endogastric curvature. The shell is fusiform in profile, reaching maximum width at or near the base of body chamber, which narrows toward the aperture. The siphuncle is large and slightly removed from the ventral side, that with the concave longitudinal profile. Siphuncle segments are short, as are chambers; septal necks recurved, connecting rings thick, bullettes at the apical end of the rings swollen. Cameral deposits are lacking.
Kayoceras is a genus of middle Silurian nautiloid cephalopods, known from Iowa and Illinois, belonging to the Discosoridae. Related genera include Discosorus, Endodiscosorus, and Stokesoceras. Kayoceras has a short, breviconic shell, like Discosorus, but with a more central siphuncle. Derivation is probably from Discosorus, through an evolutionary shifting of the siphuncle position, which has its origin in the Lowoceratidae, possibly through Tuyloceras.
