Orthoceras, also known as Orthoceratites, is a genus of extinct marine invertebrates that lived during the Ordovician Period (485 million–443 million years ago). These creatures were relatives of ammonites and squid. Orthoceras fossils can be between a centimeter and over 14 feet long. You can find them commonly on a rock matrix, most of the time limestone. The best specimens come from Morocco, Scandinavia, Sweden, and the Baltic States.

Orthoceras have been used as a carving or sculpting material for many years. It can be carved into plates, spheres, palm stones, jewelry, lock boxes, and other little trinkets. The fossil and the marine rock it's attached to are so durable that they're often used to create furniture.