Early in the Evolution of the Turtle Body (IMAGE) University of the Witwatersrand Caption Early in the evolution of the turtle body plan a gradual increase in body wall rigidity produced a division of function where the abdominal muscles became specialized for breathing, which freed up the ribs to eventually (approximately 50 million years later) become fully integrated into the characteristic turtle shell. Credit Credit: Blair Lyons (Stroma Studios) and Emma R. Schachner 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.