Reptile Species and Habitats

Reptiles include more than 9,300 species that range from the marine plesiosaurs and ichthyosaurs to the plant-eating dinosaurs to today’s snakes, lizards and crocodiles. The environment where a reptile is found can provide a big clue to the correct identification.


All reptiles, including crocodiles, snakes and lizards, are cold-blooded. Without fur or feathers to retain heat, they cannot regulate their internal body temperature and must depend on sun or shade to change the temperature of their skin.


Turtles are unique among reptiles in that they are the only vertebrates to have evolved a shell. They also have the distinction of being the oldest living reptiles. Some, like the leatherback sea turtle (Dermochelys imbricata), can live up to 100 years! Unlike other reptiles, most turtles are opportunistic omnivores and some, such as the green turtle (Chelonia mydas), migrate long distances to lay their eggs on a specific favored beach.

For over a century, turtles have puzzled scientists because morphological and molecular data have yielded conflicting conclusions about their relationship to other reptile species. Some morphological analyses positioned turtles as basal to all reptiles, while others placed them closer to lepidosaurs such as lizards, snakes and tuatara. Molecular analyses typically grouped them with crocodiles and birds.

In the new study, researchers from BU used genomic data to resolve this ancient question. They obtained samples of blood from four turtle species (Phrynops hilarii, Caretta caretta, Chelonoidis nigricans and Emys orbicularis), representing the suborders Pleurodira and Cryptodira.

Using single-copy nuclear loci dispersed throughout the genome, they analyzed 1145 ultraconserved elements, which are highly conserved and serve as a proxy for distant evolutionary relationships. The results confirmed that turtles are more closely related to crocodiles and birds than to lizards, snakes or tuatara. This resolves a long-standing dispute about the placement of turtles in the reptile tree and is at odds with most morphological and paleontological data.


Lizards are found all over the world, inhabiting deserts, beaches, forests and many other habitats. They vary in size from tiny geckos to large marine iguanas, and they can be adapted for almost any environment.

Most lizards use their tongues to catch scent particles in the air and then transfer them to their noses where special sensory cells can detect them. This allows lizards to smell, which is especially useful for finding food and potential mates. They also have a wide variety of color patterns that warn predators they are poisonous, help attract prey and display social information.

Unlike mammals, reptiles don’t sweat and need to rely on external heat sources to regulate their body temperatures. They are also cold-blooded, which means they eat less food than their warm-blooded cousins. Their dry scaly skin does not grow with them, but instead they shed it, or molt, in large flakes to make room for new skin growth underneath.

A number of lizards, such as skinks, can drop their tails and keep moving, distracting predators while they escape. These lizards can also regenerate their tails, though the new ones don’t look exactly like the old ones. In addition, some lizards (like geckos) have pads on their feet that allow them to climb vertical surfaces, and others (like snakes) can crawl up walls or trees with ease.


Snakes, a suborder of Reptilia called Squamata, are found on every continent but Antarctica. Their bodies are long and slender, their eyes fixed in their head (without eyelids), and they lack external ears or vocal cords. They focus 70% of their solitary lives on hunting, capturing, and digesting their living prey.

Most snakes are carnivorous, feeding on lizards, frogs, birds, mammals, eggs, fish, snails, worms, and other invertebrates. Unlike most reptiles, they cannot tear their food into bite-sized pieces so they swallow it whole. Their slender bodies are used to move themselves across the ground, and their scales have been designed with the same purpose as a tire tread, to grip the surface they crawl over.

Like lizards, snakes are cold-blooded and must rely on external sources of heat to regulate their internal body temperature. During hot weather, they might seek out a rock or roadside to warm themselves; to cool their bodies, they might sun themselves or find shade. Snakes can also use a special system of circulation to control their core body temperature by moving warmed blood to the center of the body and pushing cooler blood toward the edges. Moreover, they can also generate their own thermal energy through muscular contraction and by shedding their skin.


Crocodiles are semi-aquatic and live in wetlands of the tropics. They are members of the order Crocodilia, which also includes alligators and caimans.

These animals are apex predators of their habitats, stalking and ambushing prey from their hiding places under the water’s surface or near the edge of the river bank. Using their powerful tails, they can drag their victims underwater and hold them there until they drown. Their large jaws are capable of crushing even a fully grown human!

They are the most feared predators on the planet and have been for millions of years. The crocodile’s elongated snout and dark green or yellow skin are a terrifying sight for any creature they come across.

Despite being fierce predators, crocodiles are quite intelligent creatures with some advanced cognitive abilities. For example, they can recognize patterns of when prey visit the water to drink. University of Tennessee scientist Vladimir Dinets observed that crocodiles bait birds with twigs that they place on their snouts, partly submerge themselves and then catch the bird when it flies into the area to retrieve the stick.

Researchers have found that crocodiles, alligators and gharials experience sharp declines in their population during the most recent ice age. This is probably due to a combination of factors including habitat loss, illegal hunting and public perception of these animals as man-eaters.