An international paleontological research team recently reported that the True South Turtle, which lived in South Africa 280 million years ago, is the ancestor of modern turtles who survived large-scale species extinctions from Permian to Triassic. At that time, in order to avoid the harsh natural environment, they tried to dig down the hole, and in order to ensure that the digging movement of the forelimbs was strong enough, the body needed a stable support, which led to the widening of the ribs. It can be seen that turtles have shells to adapt to the environment, but not for protection, but to dig holes in the ground.
The front legs of True South Turtles are strong enough that they do not need shell protection can be added as a prerequisite.