Title: Fossil Ammonite (Sphenodiscus lenticularis) 

Date: Cretaceous, Maastrichtian Age, 60 to 70 million years ago
Location: Fox Hill Formation (South Dakota, United States)
Size: 7” H x 18.25” L
Credit: Gift of Black Hills Institute for Geological Research, In Memory of Allen Graffham
On View: Yes

The Fox Hill Formation contains a number of well-preserved fossils, including ammonites with a mother of pearl shell. These shells, once polished, creates an opalized effect that shimmers in the light.

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