Waiting to Exhale (IMAGE) Brown University Caption When they moved from water to land, animals needed to rid themselves of CO2 to avoid acid buildup. Some, like Eryops, used bone in skin and scalp to neutralize the acid, an approach still used by some modern animals. Credit Christine Janis and Museum of Natural History, Paris 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.