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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.
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.
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.
Paraloxoceras is a genus of straight shelled, orthoconic nautiloid cephalopods, now extinct, that lived during the Early Carboniferous. Fossils have been found in Europe and central Asia; the type, P. konincki, named by Flower, came from Belgium.
Murchisoniceras is an extinct genus of cephalopod Nautiloid, that lived during the Silurian from 425 to 416 mya, in what would be Europe, existing for approximately 9 million years.
Homaloceras is an extinct nautiloid cephalopod from the Middle Devonian with a strongly curved shell, included in the nautilid family Centroceratidae.
Jovellania is a genus of extinct prehistoric nautiloids from the order Oncocerida known from the Lower Devonian of Europe. Nautiloids form a broad group of shelled cephalopods that were once diverse and numerous but are now represented by only a handful of species in two genera.
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.
Brevicoceras is an extinct nautiloid genus from the order Oncocerida with wide distribution in the Middle Devonian in Eastern North America, Russia and Morocco. Nautiloids form a broad group of shelled cephalopods that were once diverse and numerous but are now represented by only a handful of species in two genera.
Ankyloceras is a genus of Early Devonian cephalopods included in the oncocerid family Karoceratidae. The type species, Ankyloceras nesnayamiense named by Zhuravleva, 1974, comes from Nova Zemlya in Russia. Other species have been found in Japan, Morocco, and Russia.
Streptoceras is a genus in the extinct oncocerid family Acleistoceratidae that plied the shallow sea floor from the Middle Silurian to the Middle Devonian. Streptoceras is characterized by a shell that is large but short in proportion (breviconic) with the ventral profile convex and dorsal profile concave in the posterior part, convex over the body chamber, then concave toward the front, like Amphycertoceras, but with a triangular shaped aperture. Streptoceras is found in the Middle Silurian of North America, in Ontario.
Shuranoceras is a genus in the extinct oncocerid family Karoceratidae that plied the shallow sea floor from the Early Silurian to the Early Devonian. Shuranoceras is characterized by a smooth, compressed, slowly enlarging orthoconic shell with a ventral submarginal siphuncle composed of complex segments. Shuranoceras was found in middle Silurian strata in Ferghana, central Asia.
Pseudorthoceratidae is an extinct family of actively mobile aquatic carnivorous cephalopods belonging to the subclass Orthoceratoidea endemic to what would be North America, Asia, and Europe during the Silurian living from 460.5—251 Ma, existing for approximately 209.5 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.
Leurocycloceras is an extinct genus of actively mobile carnivorous cephalopod, essentially a Nautiloid, that lived in what would be North America, Europe, and Asia during the Silurian from 443.7—418.7 mya, existing for approximately 25 million years.
Neosichuanoceras is an extinct genus of actively mobile carnivorous cephalopod, essentially a Nautiloid, that lived in what would be Asia during the Silurian from 436.0—428.2 mya, existing for approximately 7.8 million years.
Orthocycloceras is an extinct genus of actively mobile carnivorous cephalopods, essentially a Nautiloid, that lived in what would be Europe during the Silurian to Devonian from 428.2—412.3 mya, existing for approximately 15.9 million years.
Paradnatoceras is an extinct straight-shelled cephalopod genus that lived in what would become China during the Ordovician from 478.6 to about 461 mya, existing for approximately 17.6 Ma.
Protobactrites is an extinct nautiloid cephalopod belonging to the Orthoceratoidea that lived in what would be Europe and Asia during the Ordovician and Silurian from 466–421.3 mya, existing for approximately 44.7 million years.
Vericeras is an extinct genus of actively mobile carnivorous cephalopod, essentially a Nautiloid, that lived in what would be Europe during the Silurian from 421—418.7 mya, existing for approximately 2.3 million years.
References
- ↑ "Parasphaerorthoceras". The Paleobiology Database. Retrieved 16 July 2012.
- ↑ J. J. Sepkoski. 2002. A compendium of fossil marine animal genera. Bulletins of American Paleontology 363:1-560
- 1 2 Björn Kröger, 2008. Nautiloids Before and During the Origin of Ammmonoids in a Siluro-Devonian Section of the Tafilalt, Anti-atlas, Morocco. Special Papers in Palaeontology; the Palaeontological Association, London.
