Fossil Ammonite (Sphenodiscus) & Gastropod - South Dakota

This is a 1.6" ammonite (Sphenodiscus) and 1.3" unidentified gastropod, from the Fox Hills Formation of South Dakota. The outer shell is missing in some areas of this beautiful ammonite leaving the intricate pattern of the inner shell sutures. It has been wonderfully prepared on the hard concretion in which it was found. The gastropod is almost completely contained within the rock.

Comes with an acrylic stand

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.

What an ammonite would have looked like while alive.

More about ammonites