AN UNUSUALLY LARGE LATE DEVONIAN DISCINID BRACHIOPOD FROM FORT LEWIS MOUNTAIN, VIRGINIA
The Fort Lewis Mountain discinids most resemble O. grandis from the Late Devonian of New York but are more ovoid in shape. Other North American forms such as O. ampla and O. alleghania have very convex dorsal valves, a feature not seen in the present material, and O. magnifica has its pedicle openings in a different location. Gigadiscina lessardi from the Lower Devonian of Algeria are the same size as the Fort Lewis Mountain specimens and also have a tapering posterior margin, but are much broader with a very convex dorsal valve, but the geographic and temporal separation makes it unlikely they are closely related. All the Fort Lewis Mountain discinids were found as individual specimens rather than in clusters. Clustering, which has been observed in both fossil and extant discinids, has been interpreted as a defensive response to grazing predators such as chitons and gastropods. The lack of clustering in the Foreknobs discinids suggests that grazing predators may have been absent from the environment.