Dr. Chiari thought the shells on the saddlebacks, with their edges and corners, had evolved to make it easier for these tortoises to get back up, and set out to test her hypothesis in a study that was published Thursday in Scientific Reports. She was wrong, but her research offered additional insights into the anatomies of these endangered creatures and how they may have evolved to get back on their feet.

To test her idea, Dr. Chiari and her team first made digital 3D models of both types of shells using 89 tortoises, some in the wild and some at the California Academy of Sciences.

The researchers also determined centers of mass for the two different types of tortoises by placing them on an unstable platform and photographing them. The scientists were then able to calculate which shell would require a tortoise to expend more energy when rolling off its back.

The results suggested that a tortoise with a saddleback shell would have to work harder to get back on its feet. In general, the study found, the rounder the shell, the easier it is for the animal to right itself — seemingly an advantage for the domed tortoise.