DISARTICULATED SHELLS OF LATE ORDOVICIAN BRACHIOPODS - INFERENCES ON STRENGTH OF HINGE AND VALVE ARCHITECTURE

More than 5000 specimens of 9 species of articulate brachiopods from the Waynesville-Liberty Formation of southeastern Indiana were analyzed for the percentage of specimens disarticulated and the ratio of pedicle to brachial valves. Among biconvex species, the rhynchonellid Hiscobeccus capax displayed the highest ratio (2.66) of articulated to disarticulated specimens, an observation attributed to its cyrtomatodont hinge. Platystrophia clarksvillensis has the highest percentage of articulated specimens among the orthids, a fact attributed to the hydrodynamic stability of this species and the interlocking of the valves by the plicae around the commissure. The largest of the three concavo-convex taxa, Rafinesquina ponderosa, has the highest ratio of articulated to disarticulated specimens (3.03) and requires the fastest current velocities to transport the shells based on flume experiments. -from Author