Isle Royale Moose Skull Collection (IMAGE) Michigan Technological University Caption The researchers observed around a 16 percent decrease in skull size over a four-decade period, which is about the difference between the middle two skulls. Credit Sarah Bird/Michigan Tech Usage Restrictions please 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.