File:Megastrophia concava (fossil brachiopod) (Silica Formation, Middle Devonian; quarry at Sylvania, Ohio, USA) 2 (37320243366).jpg

Megastrophia concava (Hall, 1857) - fossil brachiopod from the Devonian of Ohio, USA. (centimeter scale)

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).

This is the exterior of a ventral valve of a moderately large strophomenid brachiopod called Megastrophia concave. It is a common species in the richly fossiliferous Silica Formation of northwestern Ohio and southeastern Michigan. This Middle Devonian unit consists of interbedded shales, calcareous shales, argillaceous limestones, and fossiliferous limestones. Common fossils include brachiopods, bryozoans, crinoids, trilobites, and other typical Paleozoic marine faunas.

Click on the above photo to zoom in and look around. In the center part of the fossil are partially eroded, tapering structures with subcircular openings. These are auloporids, an extinct group of tabulate corals. They consist of calcareous colonies of hard substrate-encrusting, trumpet-shaped corallites. They first appear in the Ordovician and go extinct in the Permian. The auloporids shown here are encrusting a moderately large strophomenid brachiopod from Ohio's famous Silica Formation, a richly fossiliferous unit.

Classification of host shell: Animalia, Brachiopoda, Articulata (a.k.a. Rhynchonelliformea), Strophomenata, Strophomenida, Strophodontidae

Stratigraphy: Silica Formation (a.k.a. Silica Shale), Middle Devonian