EVOLUTIONARY MORPHOLOGICAL-CHANGES IN THE NEW GENUS DUOFORISA - IMPLICATION FOR CLASSIFICATION AND HABITAT OF THE UNILOCULAR FORAMINIFERA

Unlike other unilocular foraminifera, the new genus Duoforisa from the Late Oligocene to Early Miocene possesses a kidney-shaped test with t wo apertures on its distal ends. It contains two distinct and successi onal species, both new, and differentiated by their apertural details. In Duoforisa rima the apertures are slit-like, and become radial in t he descendant D. diducta. Intermediate forms have transitional apertur al configurations between the slit type and radial type. accompanied a lso by a change of the test outline from subtriangular to compactly U- shaped. The evolution of the lineage occurred during a period of enhan ced upwelling in the Early Miocene and it was terminated just before t he global warming at the Early-Middle Miocene boundary. This example s uggests evolution of the unilocular foraminifera through successional morphological changes in test shape and in the aperture. Unilocular ta xa have tended to flourish or speciate in cool or upwelling environmen ts. Their contraction in the latest Early Miocene to early Middle Mioc ene was probably due to global warming and well oxygenated conditions which were widespread in the neritic domains of southern Australia.