Abstract:
A new ostracode genus Oblitacythereis containing two new subgenera (the nominotypical form and the older Paleoblitacythereis) containing two new species (O. (O.) mediterranea and O. (P.) luandaensis) and one old species (new designation, O. (P.) ruggierii (Russo)) have been demonstrated to have descended from a common ancestral stock (new genus Paleocosta) of the genus Costa, the nominate form of the tribe Costini.
This genus contains heavily costate species whose history has been one of invasion of the greater depths of Tethys, which became thermospheric in the middle Miocene. Species of subgenus Paleoblitacythereis became adapted to upper slope and warm basinal habitats and underwent considerable modification of its carapace structure. When Tethys became extinct as a marine environment at the end of the Miocene, subgenus Paleoblitacythereis was eradicated in the Mediterranean region but survived in the Atlantic, where it lives today. Its descendant subgenus Oblitacythereis invaded the newly formed Mediterranean in the Early Pliocene, structurally modified to live in cooler water.
The history of Oblitacythereis was traceable because of a detailed analysis of structural and form homology, substantiated by quantitative Theta-Rho test.
