File:Productid brachiopod (Lower Mercer Limestone, Middle Pennsylvanian; Rock Cut railroad cut, south-southeast of Dresden, Ohio, USA).jpg

English: Productid brachiopod from the Pennsylvanian of Ohio, USA. (3.8 cm across at its widest)

The Lower Mercer Limestone is a Middle Pennsylvanian-aged, laterally persistent, marine fossiliferous limestone unit in the Pottsville Group of eastern Ohio, USA. It is richly fossiliferous, principally dominated by brachiopods and crinoid stems. The fossil shown above is a productid brachiopod. Brachiopods are sessile, benthic, filter-feeding, marine invertebrates. They first appear in the Cambrian and are still alive in modern oceans. They all have two shells - most have shells of calcite (CaCO3 - calcium carbonate). Brachiopods dominated Paleozoic shallow seafloors. They were also fairly common in Mesozoic oceans. They are scarce in modern seas.

Eleven different productid brachiopods have been reported from the Lower Mercer Limestone: Kozlowskia haydenensis, Desmoinesia muricatinta muricatina, Desmoinesia muricatina missouriensis, Echinaria semipunctata knighti, Antiquatonia costellata, Antiquatonia portlockiana quadratia, Juresania nebrascensis inflatia, Linoproductus planiventralis, Linoproductus echinatus, Cancrinella bonnensis, and Krotovia paucispina.

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

Stratigraphy: Lower Mercer Limestone, Pottsville Group, Atokan Stage, lower Middle Pennsylvanian

Locality: Rock Cut railroad cut - outcrop along the southern side of Ohio Central Railroad tracks (west of milepost 134), ~southwest of Copeland Island & south-southeast of the town of Dresden, northern Muskingum County, eastern Ohio, USA (~vicinity of 40° 04’ 24.41” North latitude, ~81° 59’ 11.25” West longitude)