Tooth Marks Close-up (IMAGE) Yale University Caption This is a close-up of the tooth marks gouged in the rib bone of a large dinosaur by a mammal that lived 75 million years ago. Credit Nicholas Longrich/Yale University Usage Restrictions With credit. 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.