Brachiopods are marine animals that secrete a shell consisting of two parts called valves.
Their fossils are common in the Pennsylvanian and Permian limestones of eastern Kansas. Shale slab containing numerous brachiopods belonging to the genus Hystriculina, Americus Limestone Member, Foraker Limestone, Chase County, Kansas. Brachiopods have an extensive fossil record, first appearing in rocks dating back to the early part of the Cambrian Period, about 545 million years ago. They were extremely abundant during the Paleozoic Era, reaching their highest diversity during the Devonian Period, roughly 400 million years ago. At the end of the Paleozoic, however, about 250 million years ago, they were decimated in the mass extinction that marks the end of the Permian Period.