Fossil Ammonites (Hoploscaphites & Sphenodiscus) - South Dakota

This is a 3.45" wide section of rock that contains a Hoploscaphites nicolletii ammonite and a small, partially exposed Sphenodiscus lenticularis ammonite, collected from the Fox Hills Formation of South Dakota. The Hoploscaphites ammonite measures 2.7" wide and has some minor restoration along one edge.

The base of the rock has been cut flat to facilitate aesthetic presentation of the fossils without the need for a 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. 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.

Hoploscaphites nicolletti & Sphenodiscus lenticularis
North Central, South Dakota
Fox Hills Formation
Jeletzkytes ammonite: 2.7" wide, Rock: 3.45 x 2.9" rock
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