3.2" Iridescent Fossil Ammonite (Discoscaphites) - South Dakota

Iridescent Fossil Ammonite (Discoscaphites) - South Dakota #189352

This is a 3.2" ammonite (Discoscaphites rossi) from the Fox Hills Formation of South Dakota. The iridescence of the fossil creates a colorful display. This specimen has been meticulously prepped to expose it from the hard concretion it was found in. One edge of the remaining rock has been cut flat to act as a display base.

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.

These 70 million year old ammonites lived when South Dakota was a shallow inland sea. It was found preserved in a concretion that was split open. It then had to be hand prepared to remove the hard rock surrounding it from the shell, a very time consuming task.

More about ammonites