Endocerida is an extinct nautiloid order, a group of cephalopods from the Lower Paleozoic with cone-like deposits in their siphuncle. Endocerida was a diverse group of cephalopods that lived from the Early Ordovician possibly to the Late Silurian. Their shells were variable in form. Some were straight (orthoconic), others curved (cyrtoconic); some were long (longiconic), others short (breviconic). Some long-shelled forms like Endoceras attained shell lengths close to 6 metres (20 ft). The related Cameroceras is anecdotally reported to have reached lengths approaching 9 metres (30 ft), but these claims are problematic. The overwhelming majority of endocerids and nautiloids in general are much smaller, usually less than a meter long when fully grown.
Cameroceras is an extinct genus of endocerid cephalopod which lived in equatorial oceans during the entire Ordovician period. Like other endocerids, it was an orthocone, meaning that its shell was fairly straight and pointed. It was particularly abundant and widespread in the Late Ordovician, inhabiting the shallow tropical seas in and around Laurentia, Baltica and Siberia.
Cassinoceras is a genus of nautiloids belonging to the endocerid family Piloceratidae that comes from the late Early Ordovician of eastern North America and adjacent territories.
The Proterocameroceratidae were the first of the Endocerida. They began early in the Ordovician with Proendoceras or similar genus which had developed endocones, replacing the diaphragms of the ellesmerocerid ancestor.
Clitendoceras is a genus of cephalopods in the order Endocerida from the Lower Ordovician with an elongate shell with a slight downward, endogastric, curvature and a siphuncle that lies along the ventral margin. Common for endocerids, the chambers are short and the septa close spaced with sutures sloping forward across the back of the shell. Septal necks are short in the young, lengthening in the adult. Endocones are simple, but with the ventral side of the last formed projecting forward. The endosiphotube running down the middle is arched on top and somewhat flat on the lower side.
Mcqueenoceras is an extinct genus of early endocerid, a nautiloid from the Floian epoch of the late early Ordovician period. It was similar in overall form to Clitendoceras, from which it may have been derived. Mcqueenoceras, like Clitendoceras, has ventral siphuncle but the endocones are thicker on the ventral side and thinner on the dorsal. Also the sutures in Mcqueenoceras retreat rearward, forming lobes as they cross the venter. The type species is Mcqueenoceras jeffersonense, named by E.O. Ulrich and A.F. Foerste in 1935, and it is known from Missouri and New York. In 1956, Rousseau H. Flower named two other species, M. cariniferum and M. ventrale, both known from Maryland.
The Actinocerida are 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 canals and a narrow space along the inner side of the connecting ring known as a paraspatium. Septal necks are generally short and cyrtochoanitic, some being recumbent, some hook shaped. Most grew to lengths of about 60 to 90 cm but some, like the Huroniidae of the Silurian grew significantly larger.
Cyptendoceras is an extinct nautiloid cephalopod included in the family Ellesmeroceratidae that lived in what would be North and South America during the latter part of the Early Ordovician from about 475 – 472 mya, existing for approximately 3 million years.
Orthoceratoidea is a major subclass of nautiloid cephalopods. Members of this subclass usually have orthoconic (straight) to slightly cyrtoconic (curved) shells, and central to subcentral siphuncles which may bear internal deposits. Orthoceratoids are also characterized by dorsomyarian muscle scars, extensive cameral deposits, and calciosiphonate connecting rings with a porous and calcitic inner layer.
Endoceratidae is a family of large to very large straight shelled nautiloid cephalopods belonging to the order Endocerida that lived during the Middle and Late Ordovician. They include the largest known Paleozoic invertebrates, represented by Endoceras and Cameroceras.
Triendoceras is a genus of fairly large endocerid named by Flower (1958), included in the Endoceratidae by Teichert (1964), characterized by a holochoanitic ventral siphuncle in which the cross section through the endocones has an opening in the shape of an isosceles triangle with a sharp apex (corner) pointing down. Triendoceras is found in the upper Lower Ordovician of Quebec and New York in North America and possibly in Ohio, and in eastern Europe. The type species is T. montrealense.
Proterocameroceras is an early Endocerid from the upper Lower Ordovician belong to the Proterocameroceratidae, characterized by a rather large, straight, longiconic shell, short chambers, generally straight sutures, and large ventral siphuncle with short septal necks, thick complex connecting rings, and endocones with three endosiphuncular blades toward the apex.
Lobendoceras is a proterocameraceratid with a rather large, moderately expanded, straight shell with a large marginal siphuncle in which sutures have a broad, deep, ventral lobe and septal necks are subholochoanitic to holochoanitic.
Intejocerida is the name given to a group of generally straight shelled nautiloid cephalopods originally found in Lower and Middle Ordovician sediments in the Angara River basin in Russia; defined in the Treatise as an order, and combined there with the Endocerida in the Endoceratoidea.
Hectoceras is a genus in the nautiloid cephalopod order Discosorida from the Upper Ordovician of Australia (Tasmania), known from a few isolated siphuncle specimens.
Reedsoceras is a genus of large discosorids (Nautiloidea) in the family Westonoceratidae from the middle and upper Ordovician of North America.
Simardoceras is a genus in the discosorid family Westonoceratidae from the Middle Ordovician of Quebec.
Curt Teichert was a German-American palaeontologist and geologist, noted for his contributions to geology, paleozoic stratigraphy and paleontology, Cephalopoda, ancient and modern reefs, and correlation, the matching of strata of the same age in different locations.
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.
Selkirkoceras is a genus of armonoceratid cephalopods similar to Kochoceras of the Actinoceratidae, but with recumbent septal necks. The first siphuncular segment is large, broad, and blunt.
