Two Iridescent Fossil Ammonites (Discoscaphites) - South Dakota

This is a 7" wide section of rock that contains what appears to be two Discoscaphites conradi ammonites, collected from the Fox Hills Formation of South Dakota. These ammonites were expertly prepared before being remounted to the rock in which they were found. There are a couple bonus, partially exposed gastropods within the rock, however they are unidentified.

The bottom of the rock is cut flat for ease of display.

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.

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