Sea Cow Quadruped (IMAGE) Duke University Caption The 43 million-year-old fossil skeleton of Pezosiren, an amphibious quadruped of the sea cow family tree. Credit Thesupermat via Creative Commons Usage Restrictions Credit must be given to the creator. License CC BY 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.