Flexi Says: Ammonites are a group of extinct marine cephalopods that first appear in the fossil record around 450 million years ago and were very common in time of the dinosaurs. Most ammonites also became extinct around the same time as most dinosaurs at the end of the Cretaceous, 66 million years ago. Nautilus are the closest living relatives to ammonites. Ammonites are excellent index fossils, and it is often possible to link the rock layer in which they are found to specific geological time periods.
