Ammonites & Goniatites - Shoplivepages::jquery();?>
Ammonites are invertebrates and extinct members of the subclass Ammonoidea, class Cephalopoda. Modern members include the nautilus, squid, cuttlefish and octopus. Ammonites first appeared during the Middle Devonian Period around 400 million years ago. They became especially abundant and widespread in the seas of the Jurassic and Cretaceous periods, 175 million to 65 million years ago. Ammonites were so plentiful throughout various stages of geologic history that scientists use them as INDEX FOSSILS whereby the presence of certain types in a rock layer can denote a specific time period.