8.6" Wide Fossil Ammonite Cluster - South Dakota

This is a fossil ammonite cluster from the Fox Hills Formation of South Dakota. It's been wonderfully prepared on the hard concretion it was found in. The largest ammonite is a 3.6" Jeletzkytes nebrascensis and the total width of this cluster is 8.6". There are a number of other complete ammonites in this rock including a Hoploscaphites nicolletii and multiple Scaphites ammonites, along with fragments of shells still partially concealed in the stone.

The Hoploscaphites nicolletii appears to have been removed from the rock, cleaned and remounted, though it is still in the exact location it was found.

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.
Jeletzkytes nebrascensis, Hoploscaphites nicolletii & Scaphites sp.
South Dakota
Fox Hills Formation
Largest ammonite 3.6" wide (J. nebrascensis). Entire specimen 8.6 x 6.5"
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