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Reptiles

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Reptiles

What does this chameleon have in common with a snake?

Though they are both reptiles and seem very different, chameleons and snakes actually share several traits. For example, they both have skin covered in scales and are cold-blooded animals. But notice the distinct eyes and "horns" on the chameleon. Snakes don't have these. And some chameleons have the ability to change color.

Characteristics of Reptiles

What reptiles can you name? Snakes, alligators, and crocodiles are all reptiles. Modern reptiles live on every continent except Antarctica. They range in size from the newly-discovered Jaragua Sphaero (a dwarf gecko), at 0.6 inches, to the saltwater crocodile, at up to 23 feet.

There are four living orders of reptiles:

  1. Squamata, which includes lizards, snakes, and amphisbaenids (or “worm-lizards”).
  2. Crocodilia, which includes crocodiles, gharials ( Figure below ), caimans, and alligators.
  3. Testudines, which includes turtles and tortoises.
  4. Sphenodontia, which includes tuatara ( Figure below ).

A gharial crocodile and tuatara

A gharial crocodile ( left ). A tuatara ( right ).

Traits of Reptiles

Reptiles are tetrapods (four-legged) and ectothermic , meaning their internal temperature depends on the temperature of their environment. This is why you may see reptiles sunbathing as they use the energy from the sun to warm their bodies. Usually the sense organs of reptiles, like ears, are well developed, though snakes do not have external ears. All reptiles have advanced eyesight. Reptiles also have a sense of smell. Crocodilians, turtles, and tortoises smell like most other land vertebrates. But, some lizards, and all snakes, smell with their tongues, which is flicked out of the mouth to pick up scent molecules from the air.

Reptiles also have several adaptations for living on land. They have a skin covered in scales to protect them from drying out. All reptiles have lungs to breathe air. Reptiles are also amniotes , which means their embryos are surrounded by a thin membrane. This membrane protects the embryo from the harsh conditions of living on land. Reptile eggs are also surrounded by a protective shell, which may be either flexible or inflexible.

How Do Reptiles Reproduce?

Most reptiles reproduce sexually, meaning there are two parents involved. In some families of lizards and one snake family, however, asexual reproduction is possible. This is when only one parent is involved in creating new life. For example, the gecko females can make tiny clones of themselves without the aid of a male.

All reptiles have a cloaca , a single exit and entrance for sperm, eggs, and waste, located at the base of the tail. Most reptiles lay amniotic eggs covered with leathery or hard shell. These eggs can be placed anywhere as they don't have to be in a moist environment, like the eggs of amphibians. However, not all species lay eggs, as certain species of squamates can give birth to live young.

Unlike the amphibians, there are no larval stages of development. The young reptiles look like miniature versions of the adult. The young reptiles are generally left to fend for themselves. However, some reptiles provide care for their young. For example, crocodiles and alligators may defend their young from predators.

Vocabulary

  • amniote : Embryos are surrounded by a thin, protective membrane.
  • asexual reproduction : Reproduction involving only one individual.
  • cloaca : External opening that serves as the exit (and entrance) for the intestinal, reproductive, and urinary tracts.
  • ectothermic : Having an internal temperature that depends on the temperature of their environment.

Summary

  • Reptiles are also amniotes, which means their embryos are surrounded by a thin membrane.
  • Reptiles typically reproduce sexually and lay eggs.

Practice

Use the resources below to answer the questions that follow.

Practice I

  1. Which continent does not have any reptiles?
  2. Compare the amount of food eaten by reptiles and birds and mammals.
  3. Name three poisonous snakes found in the United States.
  4. What is the largest venomous snake anywhere?

Practice II

  1. How does the stance of reptiles compare to the stance of birds?
  2. Compare and contrast modern reptiles to modern birds. Include as many characteristics for both groups as you can.
  3. Do ancient "reptiles" have all the same characteristics as present day reptiles? Explain your answer fully.

Review

  1. Name four examples of reptiles.
  2. What is ectothermic?
  3. What are the reptilian adaptations for life on land?
  4. Compared to the amphibian egg, what is special about the reptile egg?

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