Fossil Ammonites (Hoploscaphites & Sphenodiscus) - South Dakota

This is a 4.2" wide rock nodule that contains a JHoploscaphites (Jeletzkytes) spedeni ammonite and a small Sphenodiscus lenticularis ammonite, collected from the Fox Hills Formation of South Dakota. The largest ammonite is Jeletzkytes spedeni and it measures 3" wide. A wide variety of complete and fragmented shells can also be found throughout the rock.

There is a repaired crack through the largest ammonite and through what remains of the surrounding rock.

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.

Hoploscaphites (Jeletzkytes) spedeni & Sphenodiscus lenticularis
North Central, South Dakota
Fox Hills Formation
Jeletzkytes ammonite 3" wide on 4.2 x 3.4" rock
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