Published online by Cambridge University Press: 14 July 2015
Ecphora is one of the most easily recognized gastropod genera in late Oligocene, Miocene, and Pliocene marine formations in the southeastern United States. Its generally large size, strong spiral ribs, and brown, calcitic exterior are much prized by fossil collectors. However, despite speculations by Petuch (1988), its evolutionary origins have remained obscure. The present shell microstructural and mineralogical evidence suggests that the earliest ecphoras were entirely aragonitic and that the thick calcitic outer layer of the later Miocene and Pliocene species originated as a thin calcitic crust on the crests of the ribs of a latest Oligocene or earliest Miocene species.