Orthoceras

What an orthocone was

Orthocones were nautiloid cephalopods, relatives of today's nautilus, with a straight, cone-shaped shell divided into chambers. The animal lived in the last chamber at the wide end; the others held gas and fluid to control buoyancy, linked by a tube called the siphuncle.

For a long time every straight nautiloid was filed under Orthoceras, a wastebasket name used across the Palaeozoic and Triassic. Later study of the internal structures split them into many groups. Today the genus Orthoceras means Orthoceras regulare and a few close species from Middle Ordovician limestones of the Baltic States and Sweden, about 470 to 458 million years old.

What Moroccan 'orthoceras' are

The fossils sold in Morocco are genuine orthocone nautiloids in dark limestone, usually listed as Devonian and from around Erfoud. They are cut and polished to show the chambers, and set in plates, bowls and tables, often with goniatites (early coiled ammonoids). Calling them orthoceras is a trade name, not a precise identification, and honest sellers say so.

What orthoceras cost: price data from October 2026

Asking prices read on 28 October 2026.

How to judge a polished orthoceras piece

Large plates are made from slabs of fossil-rich limestone. Look at how they are finished.

• The cones should be part of the rock, with chambers visible along their length. Cones that look stuck on, or that have no internal chambers, are carved or set.
• Many decorative plates have cones partly carved or deepened to stand out. It is normal practice, but it should be disclosed.
• A fine piece shows long cones, clear chambers and a clean polish without fills.

Care

The limestone is calcite: avoid acids, vinegar and lemon, which dull the polish. Clean with a damp cloth and dry. Large plates are heavy and break across thin sections, so support them flat.

Questions collectors ask