Alongside trilobites, ammonites are far and away the most popular group of prehistoric invertebrates. These shelled cephalopods belong to the broader Ammonoidea, which evolved over 400 million years ago during the Devonian. Keep in mind that not all ammonoids are ammonites and actual ammonites from the Ammonitida clade lived during the Jurassic and Cretaceous, a time during which they flourished.
