Orthocone Cephalopod

Name Meaning: Straight horn

Geologic Era: Silurian-Devonian

Location Discovered: Probably near Erfoud, Morocco

Size: Most under 2 feet long

Estimated Range: Worldwide

Extinction: Early Triassic (new finds suggest possible survival into the early Cretaceous)

These specimens are fairly common in rock shops, and are often sold under the name “Orthoceras.” True Orthoceras are only found in Eastern Europe and Sweden, where these specimens are nearly all from Morocco. It certainly is a type of orthocerid nautiloid, however. Specimens like this tend to be fairly inexpensive (and attractive), unless one is in the market for the very large, sculpture-like items. Only a few of the animals on my specimen have been polished; a look at the underside shows several smaller orthocerids.

These orthocerids are so common in that area of Morocco that the range where they are found is called the “Orthoceras limestone.” It’s possible that these animals, once they died, blanketed the seafloor in such numbers that they became the seafloor. Orthocerids are thought to have died our in the early Triassic, but newer finds suggest they may have made it into the early Cretaceous. It is possible that these are not true orthocerids, but just similar looking animals. If they are true orthocerids, that would make them a ghost lineage. A ghost lineage is a group of organisms that seemingly goes extinct, only to reappear much later in the fossil record. This leaves a large gap in time where we know they existed, but haven’t been found yet. The coelocanth is an good example of a ghost lineage animal (thought to have gone extinct 66 million years ago, and then reappeared alive and well in 1938).

Image Credits:

Orthoceras reconstruction: By Nobu Tamura (http://spinops.blogspot.com) – Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=19460217