Evolution of <I>Oblitacythereis</I> from <I>Paleocosta</I> (Ostracoda: Trachyleberididae) during the Cenozoic in the Mediterranean and Atlantic

Abstract

A new ostracode genus <I>Oblitacythereis</I> containing two new subgenera (the nominotypical form and the older <I>Paleoblitacythereis</I>) containing two new species (<I>O.</I> (<I>O.</I>) <I>mediterranea</I> and <I>O.</I> (<I>P.</I>) <I>luandaensis</I>) and one old species (new designation, <I>O.</I> (<I>P.</I>) <I>ruggierii</I> (Russo)) have been demonstrated to have descended from a common ancestral stock (new genus <I>Paleocosta</I>) of the genus <I>Costa</I>, the nominate form of the tribe Costini.<br/>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 <I>Paleoblitacythereis</I> 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 <I>Paleoblitacythereis</I> was eradicated in the Mediterranean region but survived in the Atlantic, where it lives today. Its descendant subgenus <I>Oblitacythereis</I> invaded the newly formed Mediterranean in the Early Pliocene, structurally modified to live in cooler water.<br/>The history of <I>Oblitacythereis</I> was traceable because of a detailed analysis of structural and form homology, substantiated by quantitative Theta-Rho test.