This is a gorgeous 4.5" wide Jeletzkytes spedeni ammonite specimen collected from the Fox Hills Formation of South Dakota. The shell is still in excellent condition. It has mostly been prepped free from the rock it was found in, though much of the rock has been left in place for presentation purposes.
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.
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.