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10.11: Reptiles

Difficulty Level: At Grade Created by: CK-12
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What does this chameleon have in common with a snake?

Though they are both reptiles, chameleons and snakes seem very different, but they 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. 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, 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).

An Indian 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. Usually their sense organs, like ears, are well developed, though snakes do not have external ears. All reptiles have advanced eyesight.

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.

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. However, 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.


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


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


Use the resources below to answer the questions that follow.

  1. What is the purpose of scales?
  2. Why can reptiles go for long periods of time without food?
  3. How are reptile teeth different than mammal teeth?
  4. How does this difference affect the types of food available to the two groups?
  5. Can you relate this difference to the metabolic requirements of the two groups? Explain your thinking fully.
  1. How does the stance of reptiles compare to the stance of birds? What other animals have stances similar to birds?
  2. Where do some birds still have scales?
  3. Compare and contrast modern reptiles to modern birds. Include as many characteristics for both groups as you can.
  4. Do ancient "reptiles" have all the same characteristics as present day reptiles? Explain your answer fully.


  1. Name some examples of reptiles.
  2. How do reptiles reproduce?

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Embryos are surrounded by a thin, protective membrane.

asexual reproduction

Reproduction involving only one individual.


External opening that serves as the exit (and entrance) for the intestinal, reproductive, and urinary tracts.


Having an internal temperature that depends on the temperature of their environment.

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Difficulty Level:
At Grade

Concept Nodes:

7 , 8
Date Created:
Nov 29, 2012
Last Modified:
Aug 30, 2016
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