Bivalves Click on photo to learn more about this fossil. Clams and their Relatives Boldfaced terms are linked to the Glossary. Lower or Middle Cambrian to Holocene. Of the fossils commonly found in Kansas rocks, clams may be the easiest to recognize because they closely resemble the shells scattered along modern seashores. Pennsylvanian bivalves in limestone, collected near Bonner Springs, Kansas.
Bivalves have a long history.
Their fossils first appear in rocks that date to the middle of the Cambrian Period, about 520 million years ago. Although the group became increasingly abundant about 400 million years ago during the Devonian Period, bivalves really took off following the massive extinction at the close of the Permian Period. Today bivalves are among the most successful occupants of the world's waterways. Nuculopsis, a Pennsylvanian clam from northeastern Kansas, from the Lawrence Shale, Douglas County. Inside the hard shell, the body of bivalves consists of two lobes, one lining each valve.