Credit: Credit: Blair Lyons (Stroma Studios) and Emma R. Schachner
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.
New research has shown that the modern tortoise breathing apparatus was already in place in the earliest fossil tortoise, Eunotosaurus africanus. This animal lived in South Africa 260 million years ago and shares many unique features with modern day tortoises, but lacked a shell.
Eunotosaurus bridges the morphological gap between the early reptile body plan and the highly modified body plan of living tortoises, making it the Archaeopteryx of turtles. PR