Evolution (IMAGE) University of Bristol Caption Ichthyosaurs rapidly evolved a large range of forms and sizes early in their evolution, but after a bottle neck at the end of the Triassic, show much slower rates and more restricted variety. Credit Ben Moon 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.