DECLINE AND CONTRACTION - THE HISTORY OF THE RELICTUAL GASTROPOD FAMILY PSEUDOLIVIDAE

The neogastropod molluscan family Pseudolividae is one of several clad es that have undergone a decline in diversity and a reduction in geogr aphical distribution during the Cenozoic. After originating in the Lat e Cretaceous (Campanian), the group peaked in number of species during the Paleocene. A drop in diversity after the early Eocene was followe d by successive contractions in geographical range at the end of the E ocene, during and at the end of the Miocene, and at the end of the Pli ocene. Like several other gastropod groups with a similar history, the Pseudolividae are almost absent from the rich Indo-West Pacific biota , with only two out of the sixteen living members of the family being known from the margins of the Indo-West Pacific region today. Relict g roups with a significant Neogene record in Europe, by contrast, typica lly occur in the living biota mainly or exclusively in the central Ind o-West Pacific. The decline and geographical contraction of the Pseudo lividae occurred despite the post-Eocene evolution of two morphologica l innovations, the parietal tooth or rib at the adapical end of the in ner lip, and lirae (spiral ribs) on the adaxial (inner) side of the ou ter lip.