Deer Mouse Body Mass Decreasing Over Time (IMAGE) Florida Museum of Natural History Caption Museum specimens, such as these deer mice in the National Museum of Natural History's division of mammals, provide invaluable records of how animals have changed over time. Credit Bryan McLean Usage Restrictions Please credit Bryan McLean. 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.