Reptile Structure and Function
Douglas Wilkin, Ph.D.
Jean Brainard, Ph.D.
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Printed: December 22, 2015
AUTHORS
Douglas Wilkin, Ph.D.
Jean Brainard, Ph.D.
www.ck12.org
C HAPTER
Chapter 1. Reptile Structure and Function
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Reptile Structure and
Function
• Give examples of reptiles.
• Give an overview of form and function in reptiles.
• Describe ectothermy in reptiles.
Why did amphibians evolve into reptiles?
It probably has to do with food and land. Having to live close to water limits the resources available to a species.
Having the ability to live away from water allowed reptiles to search for additional food.
Structure and Function in Reptiles
Reptiles are a class of tetrapod vertebrates that produce amniotic eggs. They include crocodiles, alligators, lizards,
snakes, and turtles. The reptile class is one of the largest classes of vertebrates. It consists of all amniotes except
birds and mammals. Reptiles have several adaptations for living on dry land that amphibians lack. For example,
as shown in Figure 1.1, the skin of most reptiles is covered with scales. The scales, which are made of very tough
keratin, protect reptiles from injury and prevent them from losing water.
Reptile Respiration
The scales of reptiles prevent them from absorbing oxygen through their skin, as amphibians can. Instead, reptiles
breathe air only through their lungs. However, their lungs are more efficient than the lungs of amphibians, with more
surface area for gas exchange. This is another important reptile adaptation for life on land.
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FIGURE 1.1
Crocodile Scales. These crocodiles are
covered with tough, waterproof scales.
Reptiles have various ways of moving air into and out of their lungs. Lizards and snakes use muscles of the chest
wall for this purpose. These are the same muscles used for running, so lizards have to hold their breath when they
run. Crocodiles and alligators have a large sheet of muscle below the lungs, called a diaphragm, that controls their
breathing. This is a structure that is also found in mammals.
Ectothermy in Reptiles
Like amphibians, reptiles are ectotherms with a slow metabolic rate. Their metabolism doesn’t generate enough
energy to keep their body temperature stable. Instead, reptiles regulate their body temperature through their behavior.
For example, the crocodile in Figure 1.2 is soaking up heat from the environment by basking in the sun. Because
of their ectothermy, reptiles can get by with as little as one tenth the food needed by endotherms such as mammals.
Some species of reptiles can go several weeks between meals.
FIGURE 1.2
Heat Transfer to an Ectothermic Reptile.
This crocodile is being warmed by the
environment in three ways. Heat is radiating directly from the sun to the animal’s
back. Heat is also being conducted to
the animal from the rocks it rests on. In
addition, convection currents are carrying
warm air from surrounding rocks to the
animal’s body.
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Chapter 1. Reptile Structure and Function
Other Reptile Structures
Like amphibians, most reptiles have a heart with three chambers, although crocodiles and alligators have a fourchambered heart like birds and mammals. The reptile brain is also similar in size to the amphibian brain, taking into
account overall body size. However, the parts of the reptile brain that control the senses and learned behavior are
larger than in amphibians.
Most reptiles have good eyesight and a keen sense of smell. Snakes smell scents in the air using their forked tongue
(see Figure 1.3). This helps them locate prey. Some snakes have heat-sensing organs on their head that help them
find endothermic prey, such as small mammals and birds. Staring into the Beautiful Cold-Blooded Eyes of Reptiles
at http://www.environmentalgraffiti.com/news-reptile-eyes is a pictorial display of numerous reptile eyes.
FIGURE 1.3
Snake “Smelling” the Air. A snake flicks
its tongue in and out to capture scent
molecules in the air.
See Reptiles at http://www.youtube.com/watch?v=TAtGDQkZzZ8 for an introduction to these animals.
Summary
• Reptiles are a class of ectothermic, tetrapod vertebrates.
• Reptiles have several adaptations for living on dry land, such as tough keratin scales and efficient lungs for
breathing air.
• Reptiles have a three-chambered heart and relatively well-developed brain.
Explore More
Use this resource to answer the questions that follow.
• http://www.hippocampus.org/Biology → Non-Majors Biology → Search: Reptiles
1.
2.
3.
4.
5.
6.
List the groups of animals that comprise the reptiles and describe their general characteristics.
List specialized characteristics of reptiles.
What was the outcome of the terrestrial specializations of reptiles?
Describe amniotic eggs.
Compare and contrast snakes and lizards.
What are the testudines?
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Review
1.
2.
3.
4.
Describe reptile scales and the functions they serve.
What is a diaphragm? What does it do?
Describe two senses that snakes may use to locate prey.
Pretend you are a reptile such as a lizard. Explain how you might stay warm on a cold day.
References
1. Image copyright OlegD, 2014. Crocodile scales . Used under license from Shutterstock.com
2. Karunakar Rayker. Heat transfer to an ectothermic reptile . CC BY 2.0
3. Linda Cronin. Snake “smelling” the air . CC BY 2.0
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