2.8" Fossil Ammonite (Hoploscaphites) - South Dakota
This is a 2.8" ammonite (Hoploscaphites) from the Fox Hills Formation of South Dakota. It has been wonderfully prepared on the hard concretion it was found in. Only a small portion of rock remains on the reverse side of the ammonite and acts as a stand. In addition to the ammonite, shell fragments of other ammonites and gastropods are visible imbedded in the rock.
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. Ammonites appeared in the fossil record about 240 million years. The last lineages disappeared 65 million years ago at the end of the Cretaceous.