Description
This is an Ammonite from the BearPaw Formation.
Here is a nice and quite good size Fossil Ammonite. It is a Jeletzytes crassus and was found in Montana.
This Fossil Crystal Ammonite has some great detail. It has been broken in half but it reveals the wonderful crystals inside. And it can be put back together to sit on a desk or cabinet..
This ammonite is 3 3/4 inches across and the block is4 inches by 4 1/2 inches. It has great detail and it is quite showy. Because some of the internal chambers are still hollow it allowed crystals to form.
Ammonites are extinct spiral shelled cephalopod. They are more closely related to living octopus, squid and cuttlefish. But they are also related to shelled Nautilus but more distantly. The earliest ammonoids appeared during the Devonian but the last species vanishing during or soon after the Cretaceous. And the early ammonoids had different structural shells. Because they were more prevalent during the Jurassic Period, marine sediments contain large numbers of them. This ammonite does show good detail in the exterior shell.
This fossil crystal ammonite like all others had a hard external shell and so they fossilized well. Some shells were coiled but some were also straight. Today modern cephalopods do not have the external shell.
Ammonites are excellent index fossil and linking the rock layer in which a particular species or genus is found to specific time periods is often possible. And today many ammonites are cut and polished to reveal the intricate structure of the inside shell.
