Fossil Ammonites (Hoploscaphites & Sphenodiscus) - South Dakota

This is a 5.5" wide section of rock that contains a Hoploscaphites (Jeletzkytes) spedeni ammonite and a small Sphenodiscus lenticularis ammonite, collected from the Fox Hills Formation of South Dakota. The largest ammonite is Hoploscaphites and it measures 3" wide, while the Sphenodiscus ammonite measures 1.3" wide. Both ammonites exhibit some iridescence, though the Sphenodiscus ammonite has the most color-play of the two. The Hoploscaphites was removed from the rock it was found in, prepared and then remounted to this rock.

It is accompanied by an acrylic display stand to assist with presentation.

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.

What an ammonite would have looked like while alive.
What an ammonite would have looked like while alive.
Hoploscaphites (Jeletzkytes) spedeni & Sphenodiscus lenticularis
North Central, South Dakota
Fox Hills Formation
Jeletzkytes ammonite: 3" wide, Rock: 5.5 x 3.7" rock
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