TAXONOMY AND PALAEOECOLOGY OF PINNA (P.) CRETACEA (SCHLOTHEIM, 1813) FROM THE UPPER CRETACEOUS OF THE SERGIPE BASIN, BRAZIL

The bivalve species Pinna (Pinna) cretacea (Schlotheim, 1813) is redescribed from Turonian and presumed lower Coniacian beds of the Sergipe Basin, north-eastern Brazil, with the description of the new subspecies P. (P.) cretacea brevis from the upper Turonian and/or lower Coniacian. Some of the specimens of P. (P.) cretacea show predation scars of different types. As these bivalves lived with their posterior end of the valves projecting above the sediment surface, they were at a constant risk of damage by predators, although able to repair their shells relatively easily. The subspecies P. (P.) cretacea brevis shows a higher repair frequency than the nominotypical subspecies, which is explained mainly by morphological features (e.g. size, outline, inflation and ornamentation) and by its ability to repair the damaged shell. Thus, the wide, less convex, strongly ribbed shells of the subspecies brevis display a higher percentage of predation scars. In addition, different life habits of the two subspecies may have caused differences in repair frequency. As both subspecies possess thin shells, shell thickness does not appear to be significantly correlated with repair frequency.