5.7" Iridescent Fossil Ammonite (Sphenodiscus) - South Dakota

This is a 5.7" Sphenodiscus sp. ammonite specimen that was collected from the Fox Hills Formation of South Dakota. The shell is still intact and exhibits excellent iridescence. It's been wonderfully prepared free from the hard concretion it was found in.

There is a calcite seam that runs through the ammonite and one side has been coated in a layer of sealant/epoxy. Comes with an acrylic display stand.

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. Ammonites appeared in the fossil record about 240 million years. The last lineages disappeared 65 million years ago at the end of the Cretaceous.

Sphenodiscus sp.
South Dakota
Fox Hills Formation - Trail City Member
Ammonite 5.7" Wide
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