Both tortoises and turtles are able to flip themselves over from a supine position. Adaptations such as tall, uneven shells assist in creating an imbalance that allows the turtle or tortoise to roll back to its feet.
Turtles and tortoises that feature smooth, flat shells usually have longer necks to compensate, allowing them to use their necks as pivots while pushing off with the legs in order to return to a right-sided position. Those that have more moderately shaped shells use a combination of those previous strategies and often have to thrash quite a bit to right themselves. Aggressive male tortoises often try to flip over opponents in territorial disputes.