Image of Mysterious Tissue 'Aspidin' (IMAGE) University of Manchester Caption By examining the microscopic structure of these skeletons, they were able to identify the mysterious tissue 'aspidin' and provide new insight into the evolution of our skeleton. Credit Image from Keating et al. 2018 Usage Restrictions None 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.