Sphenodiscus lenticularis
Ammonite
Late Cretaceous
Fox Hills Formation
Corson County, Montana, USA

Nice 0.7” ammonite. Colorful sutures.

Cephalopod.

Sphenodiscus is an ammonite genus that appeared near the end of the Cretaceous Period.  It was widespread in the last 5 million years of that period – known from North America, Brazil, Europe, Jordan, and Nigeria.

Here’s a cool little Sphenodiscus with the mother-of-pearl shell layer still present.