These bivalve fossils were found in the Niobarra and Pierre formations of the Western Interior Seaway. The Inoceramus sp. clams were one of the more common fossils found from the Cretaceous Period (Mesozoic Era). Some clams could grow over a meter in diameter.
|Cretaceous Period Map from Wikipedia.org|
These specimens were on display in July 2011 at the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania. See my write up of that trip: CLICK HERE.