Hammerhead Shark (IMAGE) University of Colorado at Boulder Caption A new study led by the University of Colorado at Boulder indicates several species of small hammerhead sharks living today stemmed from one large ancestor living some 20 million years ago, evolving twice at different times and places. Credit Terry Goss 2008 Marine Photobank 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.