2.55" Ammonite (Hoploscaphites) - South Dakota

This is a 2.55" ammonite (Hoploscaphities nicolletii) fossil collected from the Fox Hills Formation of South Dakota. It was left partially embedded in the concretion it was found in. The base of the rock has been cut flat making for an aesthetic 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.
What an ammonite would have looked like while alive.
Hoploscaphities nicolletii
Corson County, South Dakota
Fox Hills Formation - Trail City Member
Ammonite 2.55" Wide
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