Amphibian literally means “having a double life,” and many amphibians are just as comfortable on land as they are living in the water. Amphibians may be the most familiar animals that often live on land and in the water, but several other animals thrive in both domains as well, including crocodilians, turtles and even some fish.
American alligators (Alligator mississippiensis) historically ranged throughout the coastal plain of the southeastern United States as far north as Virginia. Currently, the species is found in a much smaller range. These long-lived reptiles walk on land to travel between water sources, to lay eggs and access basking locations. When entering the water, alligators will lie on their bellies, push with their legs and slide into the water. Alligators are better swimmers than runners, but are capable of running 10 miles per hour or more for short bursts. Alligators aren't the only crocodilians suited to this dual lifestyle; all 23 crocodilian species are well adapted to walking on land and swimming in the water.
The pretty black-and-yellow spotted turtle (Clemmys guttata) is a North American native that are equally at home on land or in the water. Though not the accomplished swimmers that slider (Chrysemys sp.) or softshell (Apalone sp.) turtles are, they do swim well. Spotted turtles eschew deep water and typically inhabit wetlands and shallow ponds with mud or sand bottoms. Most food is consumed in the water and consists of fish, invertebrates and vegetation. While on land, the 4-inch spotted turtles are at high risk of predation, and -- when possible -- they will retreat to the water if frightened. Besides the spotted turtle, all aquatic species can walk on land; though some of the land-loving tortoises cannot effectively swim.
Southern two-lined salamanders (Eurycea cirrigera) inhabit most of the southeastern United States. These small amphibians deposit eggs in the water that hatch into fully aquatic larvae. Adults are quite capable on land, though they often flee to the water if threatened by a predator. As with all members of the family Plenthodontidae, two-lined salamanders don’t have lungs. Larvae breathe through their gills while in the water, and adults breathe through their moist skin. In addition to the two-lined and dozens of other salamander species, many frogs are equally comfortable walking or hopping on land and swimming in the water.
Six species of the superorder Dipnoi are called lungfish. Native to South America, Africa and Australia, these fish have better control of their fins than most fish and can use them to walk -- albeit awkwardly -- on land. Lungfish use a swim bladder to gulp air from the surface, though some species also have rudimentary gills for breathing underwater. Lungfish use their air-breathing and land-walking capabilities to aestivate in the dry mud when their pond dries up or travel to a new water source. Additionally, lungfish may gulp air from the surface when the oxygen levels in their pond drops too low.