Fossil Ammonites (Jeletzkytes & Sphenodiscus) - South Dakota

This is a 4.2" wide rock nodule that contains a 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 ago and they barely survived several major extinction events. The last lineages disappeared 65 million years ago at the end of the Cretaceous.

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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