the ammonites anct subgroup of cephalopods.

age ammonite ammonites ammonoidea anct animal animals archaeological archeology are background basic biology cambrian casing cephalopods closeup distance earth evolution excavation extinct fossil fossils geologic geological geology history increasing jurassic limestone logarithmic macro manner mineral minerals nautilus old opening paleontology period prehistoric rock rolled science seashell shape shell skeleton snail spiral stone subgroup tapering time trilobites tube which