The shell of a hatchling turtle is flexible, because it had to curl up inside the egg. The flexibility comes from bands of soft material (sutures) where the bones join. As the hatchling grows, the soft material stiffens or disappears, and the edges of the bones get jagged like interlocking teeth, making the shell rigid. The scales of material on the top of the shell (scutes), which are made of keratin like fingernails, do not grow. Instead, new scutes are formed under the old ones. Because a turtle grows faster during warm seasons than cooler ones, the scutes form growth rings like a tree that can be counted to estimate age. Depending on the species, the count is not necessarily reliable, since many turtles shed off old scutes. Regardless, turtles are famous for their long lives, with many species living more than 100 years.

Walking is challenging for turtles because of their sprawled limbs on wide bodies that are close to the ground. Any tilting from side to side may cause their shells to scrape the ground. A typical walking gait of a four-legged animal (quadruped) is a regular sequence of left hind leg, right front leg, right hind leg, and left front leg. Three legs are on the ground at once, making a stable tripod, except during the transitions when weight shifts from one leg to the next. What walking turtles do is take their next step, making a new tripod, before moving a leg from the previous tripod. This makes for a slow walk. When turtles make a run for it, you can see their shells tilting back and forth during the weight transitions, even banging on the ground. Perhaps that is why many turtles swim, propelling themselves with movements of front and hind limbs.