Orthoceras
Orthoceras is a genus of extinct nautiloid cephalopod restricted to Middle Ordovician-aged marine limestones of the Baltic States and Sweden. This genus is sometimes called Orthoceratites. Note it is sometimes misspelled as Orthocera, Orthocerus or Orthoceros.
| Orthoceras | |
|---|---|
| Artist's reconstruction of O. regulare | |
| Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Cephalopoda |
| Order: | †Orthocerida |
| Family: | †Orthoceratidae |
| Genus: | †Orthoceras Bruguière, 1789 |
| Species: | †O. regulare |
| Binomial name | |
| †Orthoceras regulare (Schlotheim, 1820) | |
Orthoceras was formerly thought to have had a worldwide distribution due to the genus' use as a wastebasket taxon for numerous species of conical-shelled nautiloids throughout the Paleozoic and Triassic. Since this work was carried out and re cataloging of the genus, Orthoceras sensu stricto refers to Orthoceras regulare, of Ordovician-aged Baltic Sea limestones of Sweden and neighboring areas.
These are slender, elongate shells with the middle of the body chamber transversely constricted, and a subcentral orthochoanitic siphuncle. The surface is ornamented by a network of fine lirae (Sweet 1964:K224). Many other very similar species are included under the genus Michelinoceras.