Polar Front in the Oligocene (IMAGE) University of South Carolina Caption The boundary between the easterly and westerly prevailing winds (the polar front) during the Oligocene epoch (yellow line) was determined from fossil data. Credit Image: adapted from <I>Nature</I>. Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.