EVOLUTION OF THE RUDIST BIVALVE AGRIOPLEURA KUHN (RADIOLITIDAE, HIPPURITIDA) FROM THE MEDITERRANEAN REGION

The genus Agriopleura (Radiolitidae) is restricted to the Lower Cretaceous of the Mediterranean region, including the Middle East, and this rudist is apparently absent from the New World. Agriopleura underwent a size increase from late Hauterivian to mid-late Barremian, matching Cope's rule, followed by a Lilliput phase in the early Aptian. The relative development of radial bands increased through time and represents a key evolutionary index. During its evolution, Agriopleura increased in species diversity and expanded geographically onto the European Mediterranean Tethyan margin from the late Hauterivian to Barremian, after which it disappeared from the region (pseudotermination). In the lower Aptian, after a Lazarus gap, the genus reappears in the southern Mediterranean Tethyan margin. Assuming that Archaeoradiolites is the direct descendant of Agriopleura, the disappearance of the genus in the mid-Aptian was a pseudoextinction and this coincided with a major crisis of shallow carbonate settings and their associated biota. The definition of Agriopleura species is based on a set of qualitative and quantitative external and internal characters. Five species are recognized: three Barremian species, Agriopleura blumenbachi, the type species, A.marticensis and A.carinata; one lower Aptian species A.libanica; and a new species A.sequana restricted to the upper Hauterivian. Principal component analysis is used to test the distinctiveness of the species and the pattern of relationships of some of their key quantitative characters.