Taxonomy and stratigraphy of Early Cretaceous species of Debrunia Masse and Fenerci-Masse (Hippuritida, Monopleuridae) of the Mediterranean region

Abstract

The genus Debrunia is characterized by its myophoral organisation: the left valve posterior myophore is an erect plate, the anterior is a bulge or a crest, myophores of right valve are on shell wall, the ligament groove is inconspicuous and the cardinal apparatus tends to be shifted posteriorly. Shell habit varies from low conical to elongated cylindrical, and the shape of the left valve ranges from capuloid to flat. The taxonomic revision of Debrunia species of the Mediterranean regions reveals the presence of thirteen species, among which seven are described as new. Multiple Component Analysis and Cluster Analysis document the existence of five groups of species in correspondence with the height of the left valve and the commissural diameter. The longevity of Debrunia is high, 32 Myr, whereas its species have shorter durations which account for a significant biostratigraphic potential within the Valanginian–Albian time span. Debrunia has its FO (First occurrence) in the lower Valanginian and its LO (Last occurrence) in the Albian. Its developmental phase starts in the Hauterivian, marked by an increasing species diversity and a biogeographic expansion; and peaks in the late Barremian, followed by a collapse in diversity and a specific turnover, coeval with the “Agriopleura extinction event”. The mid-Aptian crisis is expressed by a drastic decline in species diversity, controlled by the overall restriction or demise of carbonate platforms in European regions. As elevators, Debrunia species tend to build dense monospecific aggregations and some of them possess a remarkable bioconstructional potential. The contribution of Debrunia to rudist communities is significant throughout the history of the genus.