4.6" Fossil Ammonite (Placenticeras) - South Dakota

This is a 4.6" ammonite (Placenticeras) from the Fox Hills Formation of South Dakota. It has been wonderfully prepared on the hard concretion it was found in. The ammonite is iridescent on the back side, while the front shows the intricate suture pattern of the inner shell.

Ammonites were predatory cephalopod mollusks that resembled squids with spiral shells. They are more closely related to living octopuses, though their shells resemble that of nautilus species. True ammonites appeared in the fossil record about 240 million years ago during the Triassic Period. 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.
Placenticeras meeki
South Dakota
Fox Hills Formation
4.6", 4.9" total height
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