File:Leptaena sp. (fossil brachiopod) (Delaware Limestone, Middle Devonian; Olentangy River at Lazarus Run, Delaware County, Ohio, USA).jpg

English: Leptaena sp. - fossil brachiopod in limestone from the Devonian of Ohio, USA.

The Delaware Limestone is a significant carbonate unit in the Devonian of central and northern Ohio. It's actually part of a much more widespread sheet of Devonian carbonates that extends from New York State to the Midwest. The Delaware Limestone represents deposition in a subtropical, shallow-water, carbonate platform environment. The rocks are principally micritic limestones, fossiliferous wackestones, and fossiliferous packstones. Fossils are typical Paleozoic shallow marine invertebrates.

The thin-bedded Delaware Limestone is underlain by the thick-bedded Columbus Limestone (also Devonian). The contact is a prominent disconformity (a type II sequence boundary). Biostratigraphic studies have shown that one conodont biozone is missing at the Columbus-Delaware contact in central Ohio, probably representing ~1 to 3 million years. The Delaware Limestone is overlain by soft gray clayshales of the Olentangy Shale (lower Upper Devonian).

The fossil seen here is a distinctive strophomenid brachiopod called Leptaena. It is characterized by having prominent concentric wrinkles on both the dorsal and ventral valves. This genus has been reported from the Ordovician to the Mississippian.

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), Strophomenida, Rafinesquinidae

Stratigraphy: basal Delaware Limestone, upper Eifelian Stage, upper Middle Devonian

Locality: riverside sample along the eastern banks of the Olentangy River, immediately north of the mouth of Lazarus Run, west of Chapman Road & north of Winter Road, northeastern Liberty Township, southern Delaware County, central Ohio, USA (vicinity of 40° 13' 59.4" North latitude, 83° 03' 40.05" West longitude)