Here is a picture of a Placenticeras meeki ammonite fossil at
the Museo di Paleontologia at Sapienza University of Rome Italy.
Creatures like this existed in the western interior seaway at the time
of the upper/late Cretaceous Period (ICS geological timescale:
Maastrichtian; 70 million years ago). Fossil was found in Cheyenne River of South Dakota USA.
Image taken in June 2014.