FEATURE | TORTOISE SHELLS While tortoises and turtles may be well protected from predators in their shells, this protection has come at a price. The original ancestors of turtles had a flexible rib cage, just as we do, and they took in atmospheric air in a similar fashion, with their rib cage expanding and contracting as they breathed in and out.
Yet this situation has now altered significantly, because the ribs of chelonians (as tortoises and turtles are collectively known) have become locked into the shell, providing structural support but sacrificing their flexibility as a result.
Tracking this development
The question that has long fascinated scientists is how and when this transition occurred. Until recently, the oldest known fossil turtles, dating back about 215 million years, had fully developed shells,…