A Mass Extinction's Effect on Body Size (VIDEO) University of Pennsylvania This video is under embargo. Please login to access this video. Caption Penn paleontologist Lauren Sallan explains her research on how a mass extinction event 359 million years ago had a huge and lasting impact on the body sizes of vertebrates. Credit University of Pennsylvania Usage Restrictions In context of reporting 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.