Orthoceras fossil map
Where fossils of Orthoceras have been found, shown on the Earth as it looked about 420 million years ago and on today’s map.
Dots are fossil collections recorded in the Paleobiology Database. The “then” view moves today’s fossil sites back to their positions 420 million years ago (the time slice nearest the median age of the fossils) using the Merdith et al. (2021) plate model; positions are approximate. Open on the timeline map →
| Group | Ammonites & nautiloids |
|---|---|
| Lived | 483.4–205.7 million years ago (Tremadocian to Norian) |
| Periods | Ordovician, Silurian, Devonian, Carboniferous, Permian, Triassic |
| Family | Orthoceratidae |
| Named by | Breynius 1832 |
| Fossil records | 570 occurrences at 355 locations (PBDB) |
| Found in | United States, UK, China, Italy, Canada, Morocco, Czechia, Sweden, South Africa, Germany … |
| Rock formations | txn:103321, Skaneateles, Geneseo, Gydo, Overton, Moscow |
About Orthoceras
Orthoceras, from Ancient Greek ὀρθός (orthós), meaning "straight", and κέρας (kéras), meaning "horn", 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 and misspelled as Orthocera, Orthocerus, or Orthoceros.
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 (orthocone) 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. Many other very similar species are included under the genus Michelinoceras.
Text in “About” is quoted from the Wikipedia article Orthoceras (revision 1368001467), licensed under CC BY-SA 4.0; introduction excerpted verbatim, formatting removed. Ages, family, authority and fossil records: Paleobiology Database, accessed 22 October 2026. Ages are those of the rock layers the fossils were found in.
