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. They were found preserved in concretions when split open. They then had to be hand-prepared to remove the hard rock surrounding them from their shells, a very time consuming task.

Ammonites were predatory cephalopod mollusks that resembled squids with spiral shells. They are more closely related to living octopuses, though their shells resemble that of nautilus species. True ammonites appeared in the fossil record about 240 million years ago during the Triassic Period. 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