This Specimen has been sold.
1.9" Iridescent Discoscaphites Ammonite - South Dakota
This is a rather nice 1.9" wide Discoscaphites conradi ammonite specimen from the Fox Hills Formation of South Dakota. It's been wonderfully prepared from the hard concretion in which it was found. The rock has been cut flat to allow for aesthetic presentation.
Ammonites were predatory mollusks that resembled a squid with a shell. These cephalopods had eyes, tentacles, and spiral shells. They are more closely related to a living octopus, though the shells resemble that of a nautilus. True ammonites appeared in the fossil record about 240 million years ago. The last lineages disappeared 65 million years ago at the end of the Cretaceous.