Excellent 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 ammonites are a 2.15" Hoploscaphites nicolletti and a 1.7" Discoscaphites gulosus. The total height of this cluster is 4.3". There are a number of complete Hoploscaphites nicolleti ammonites, along with fragments of shells still partially concealed in the stone.

There are crack repairs through the Hoploscaphities nicolletii and both the Hoploscaphites spedeni and Discoscaphites gulosus ammonites were removed from the rock, prepped and then remounted to the original portion of the rock they were found in.

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.

More about ammonites