In short: ammonites were extinct marine cephalopods, relatives of today’s squid and octopus, with coiled chambered shells. They lived for more than 300 million years, from the Devonian until the end of the Cretaceous, and disappeared in the same extinction event as the dinosaurs.
What was an ammonite?
An ammonite lived in the last chamber of its shell, with tentacles extending from the opening. The older chambers behind it were filled with gas and fluid, letting the animal control its buoyancy. The walls between chambers created intricate lines on the shell, called sutures, which are one of the most beautiful features of polished specimens.
Ammonite, nautilus or orthoceras?
- Ammonites: extinct; usually complex, wavy sutures.
- Nautilus: still alive today; simple, gently curved sutures.
- Orthoceras: straight-shelled nautiloids, not ammonites, commonly sold from Morocco.
Why geologists love ammonites
Ammonite species evolved quickly and spread widely across the oceans. Each species lived for a relatively short time, so finding one helps geologists date the rock it came from. They are classic “index fossils.”
Ammonites from Morocco
Morocco produces ammonites of several ages, from Devonian goniatites of the Anti-Atlas to Jurassic and Cretaceous species. Perisphinctes, with its ribbed, evolute shell, is a Jurassic genus popular with collectors.
Natural or polished?
Some ammonites are presented natural, in their rock matrix. Others are cut and polished to reveal the internal chambers and sutures. Both are genuine fossils; the choice depends on whether you prefer a geological look or a decorative finish.
Tips for choosing an ammonite
- Look for a clear identification and size.
- Check that the coil and ribs are well defined.
- On polished pieces, look for sharp, visible sutures.
- Ask whether any part has been filled or repaired.