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Reptiles have lived on earth for over 300 million years. Reptiles include snakes, alligators, crocodiles, caimans, lizards, and turtles. Only snakes, lizards, and turtles live in the Pacific Northwest. Reptiles are vertebrates, meaning they have an internal skeleton with a backbone. All reptiles are tetrapods (they all have 4 legs or in the case of snakes, their ancestors had 4 legs).
Reptiles evolved as terrestrial or land-dwelling creatures. They have thick skin that protects them from drying out and their toes have claws. Reptiles are amniotes. Their eggs have a waterproof shell and contain amniotic fluid. Amphibians such as salamanders may look like reptiles, but differ from them in that their skin is thin and moist, their toes have no claws, and their eggs are gelatinous and have no shell.
Most reptiles are ectotherms or cold-blooded. They use their environment to warm or cool their bodies. For example, some reptiles use the sun to regulate their body temperature. These reptiles (mostly lizards) are called heliotherms. They not only control the amount of time they spend in the sun, but also control their orientation to the sun and the amount of their body that is in the sun. Other reptiles (mostly snakes) derive heat from warm surfaces. These reptiles are called thigmotherms. Most reptiles probably use both methods of warming during their lives.
The fluctating temperature of most reptiles is closely tied in with their low energy requirements. The energy requirements of most reptiles is a tenth, a fifth or even less than those of a comparable sized endotherms (birds and mammals). Although a reptile is capable of short bursts of energy to capture prey or escape predators, they are incapable of sustaining long chases or long active escapes from danger. In other words, most of a reptile's life is slow moving.
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