File:Productid brachiopod (Lower Mercer Shale, Middle Pennsylvanian; Rock Cut, Muskingum County, Ohio, USA) 1 (23473015308).jpg

Productid brachiopod in shale in the Pennsylvanian of Ohio, USA.

The Pottsville Group is a Pennsylvanian-aged cyclothemic succession in eastern Ohio that contains nonmarine shales, marine shales, siltstones, sandstones, coals, marine limestones, and chert ("flint"). The lower Pottsville dates to the late Early Pennsylvanian. The upper part dates to the early Middle Pennsylvanian. The Lower-Middle Pennsylvanian boundary is apparently somewhere near the Boggs Member (?).

The rock shown above is gray shale from the Lower Mercer Shale, a marine unit that caps the Lower Mercer Limestone in the Pottsville Group. The fossil at center is a productid brachiopod. Brachiopods are sessile, benthic, filter-feeding, marine invertebrates. They first appear in Cambrian rocks and were abundant in Earth's oceans throughout the Paleozoic. They were also common in Mesozoic oceans, but are scarce in modern oceanic biotas. Brachiopods have two shells, called valves, that are usually calcareous (made of calcite - CaCO3 - calcium carbonate). Each shell of a brachiopod is bilaterally symmetrical, unlike each shell of a bivalve (clam).

Classification: Animalia, Brachiopoda, Articulata (a.k.a. Rhynchonelliformea), Strophomenata, Strophomenida, Productidae

Stratigraphy: Lower Mercer Shale (just above the Lower Mercer Limestone), Pottsville Group, lower Atokan Stage, lower Middle Pennsylvanian