There are about 250 species of turtles, about 50 of which live in North America north of Mexico. Some turtles live only on land, but others spend almost their entire life in the sea. Most other species dwell mainly in fresh water or live about equally on land and in fresh water. Many turtles live their entire life within a few miles or kilometers of where they were hatched. But large numbers of sea turtles migrate thousands of miles or kilometers from their birthplace.
Turtles vary greatly in size.
Sea turtles, all of which swim rapidly, rank as the fastest turtles. On land, many kinds of turtles are slow, lumbering creatures. But some land turtles can move with surprising speed. For example, the smooth softshell turtle, a freshwater species of North America, often can outrun a human being on level ground. The first turtles lived more than 185 million years ago.