Ammonites are the most popular fossil around the world. Their beautifully patterned shell are the most distinctive of all fossil groups. We also include Goniatites, and Nautilus's in this category.
Ammonites are now extinct, and were actually a type of mollusc, more closely related to living squid, and cuttlefish. The earliest Ammonites appear during the Devonian, and the last species died out at the end of the Cretaceous.