File:Megastrophia concava (fossil brachiopod) (Silica Formation, Middle Devonian; quarry at Sylvania, Ohio, USA) 1 (36697604723).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 upper part of the fossil, the shell is covered with a pitted structure. That is an encrusting sheet-like bryozoan. Bryozoans, or "moss animals", are colonial lophophorates that are common in the Paleozoic and Mesozoic fossil records. They are still alive in modern oceans. Many make a hard, calcareous skeleton that is readily preserved as a fossil, although usually in a fragmented state. Encrusting bryozoans on shells and hardgrounds usually allow for examination of complete colonies. Some encrusting bryozoans consist of a just a holdfast with the upright portion of the colony detached (broken away).

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

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