Fossil Ammonite (Sphenodiscus) & Gastropod - South Dakota

This is a 1.6" ammonite (Sphenodiscus) and 1.3" unidentified gastropod, from the Fox Hills Formation of South Dakota. The outer shell is missing in some areas of this beautiful ammonite leaving the intricate pattern of the inner shell sutures. It has been wonderfully prepared on the hard concretion in which it was found. The gastropod is almost completely contained within the rock.

Comes with an acrylic stand

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.
Sphenodiscus lenticularis, unidentified gastropod
South Dakota
Fox Hills Formation
1.6" ammonite, 1.3" gastropod, 1.6 x 1.4" rock
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