Ammonite

An ammonite had a tightly coiled shell and belonged to an extinct group of shelled cephalopods, so none are alive today.

What the glossary says

Ammonoid — “A member of the subclass Ammonoidea, an extinct group of shelled cephalopods known from the Devonian to the end of the Cretaceous. Most but not all ammonoids had planispiral, tightly coiled shells. Ammonoids are also sometimes called “ammonites”, although that term more strictly applies to a subgroup of ammonoids.”

U.S. National Park Service, “Glossary of Paleontological Terms”. Quoted word for word. Courtesy of the National Park Service.

A coiled ammonite fossil exposed in a block of pale limestone, seen close up. — Real photographAn ammonite shell in a block of limestone. Ammonites lived in the sea for hundreds of millions of years; their coiled shells are among the commonest fossils a child can find on a British beach.ArtEvent ET/Shutterstock.com · Shutterstock Standard License · Licence record

Where this word appears on Triassic Water

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Sources

The definition: U.S. National Park Service, “Glossary of Paleontological Terms”, dated August 13, 2024 on the page itself, https://www.nps.gov/subjects/fossils/glossary-of-paleontological-terms.htm, read 23 September 2026. A work of the U.S. Government, in the public domain. Courtesy of the National Park Service.
How this page is made: The definition is quoted exactly. The one plain sentence under the word is ours, and it may not add a number, a date, a place or a living thing the definition does not already name. The picture carries its own credit.