What is the difference between turtles, terrapins, and tortoises?
11 July 1997
Turtles, terrapins, and tortoises are members of the order Testudines, a division of the class Reptilia. The primary difference between the three has more to do with where they live than how they look. In fact, use of the three terms varies in different parts of the world.
In the United States, all freshwater, marine and most land Testudines are known as turtles. The species of Testudines found only in the brackish waters of marshes and river inlets along the coast is called a terrapin. Totally terrestrial Testudines are tortoises.
Turtles are the most ancient of all living reptiles. They first appeared on earth some 200 million years ago and have remained relatively unchanged. Their survival is most likely due to one of nature’s most successful designs – the shell.
The shell is actually fused bone, consisting of the rib cage and spinal cord. The shells of water turtles are much flatter and more streamlined than land turtles, creating less water resistance when swimming. All aquatic turtles have webbed feet that help them displace water with each stroke.
More than 200 modern species of turtles live in the warmer parts of the world, populating every continent except Antarctica and occurring in every ocean except the Arctic. More than two-thirds of all turtle species live in freshwater.
Twenty species of turtles have been recorded in North Carolina; all but one, the box turtle, are chiefly aquatic. North Carolina’s turtle population includes both the smallest and largest species in the world. The bog turtle, found in western North Carolina, is a rare turtle reaching a mere 3-4 inches in length. The leatherback sea turtle is also rare and can have a shell length of more than 72 inches and weigh up to 1,500 pounds.
Terrapins, often called diamondbacks because of the angular rings on their shells, are the only turtles in the world that live exclusively in brackish water. They have a light colored neck with small dark markings, a yellow plastron (lower shell) and webbed feet like freshwater turtles. Female terrapins are much larger than males, more so than any other North American turtle.
Tortoises are strictly terrestrial. Their blunt, clubbed-shaped feet are well designed for walking on land. Most of the nearly 50 tortoise species live in hot, dry regions of the southern parts of the world. Their dome-shaped shells and elephant-like feet with short toes and no webbing differentiate them from aquatic turtles and terrapins. The only tortoise native to the U.S. is the gopher tortoise found in sandysoil regions of southern South Carolina, Georgia, Florida and Louisiana.
Whether aquatic or land dwellers, almost half of the world’s Testudines are at risk because of habitat degradation, hunting and environmental pollution. In North Carolina, seven species native to the state, including all five sea turtles, are considered threatened, endangered or at risk of extinction.