Reptiles
Jessica Harwood
Douglas Wilkin, Ph.D.
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AUTHORS
Jessica Harwood
Douglas Wilkin, Ph.D.
EDITOR
Douglas Wilkin, Ph.D.
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Printed: November 12, 2015
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Jane Willan
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C HAPTER
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Chapter 1. Reptiles
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Reptiles
Describe the main features of reptiles.
Define ectothermic.
Identify reptilian traits for life on land.
Describe reptile reproduction.
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.
2.
3.
4.
Squamata, which includes lizards, snakes, and amphisbaenids (or “worm-lizards”).
Crocodilia, which includes crocodiles, gharials ( Figure 1.1), caimans, and alligators.
Testudines, which includes turtles and tortoises.
Sphenodontia, which includes tuatara ( Figure 1.1).
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FIGURE 1.1
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.
Summary
• Reptiles are also amniotes, which means their embryos are surrounded by a thin membrane.
• Reptiles typically reproduce sexually and lay eggs.
Explore More
Use the resources below to answer the questions that follow.
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Chapter 1. Reptiles
Explore More I
• Fun Facts About reptiles and Amphibians at http://nationalzoo.si.edu/animals/reptilesamphibians/facts/
1.
2.
3.
4.
Which continent does not have any reptiles?
Compare the amount of food eaten by reptiles and birds and mammals.
Name three poisonous snakes found in the United States.
What is the largest venomous snake anywhere?
Explore More II
• Greatest Misconception 1: Birds Evolved from Dinosaurs at http://www.youtube.com/watch?v=EUBcH
OYls20 (2:06)
MEDIA
Click image to the left or use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/117081
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.
2.
3.
4.
Name four examples of reptiles.
What is ectothermic?
What are the reptilian adaptations for life on land?
Compared to the amphibian egg, what is special about the reptile egg?
References
1. Crocodile: Francesco (Flickr:spaceodissey); Tuatara: User:Dumplestilskin/Wikipedia. A gharial crocodile
and tuatara . Crocodile: CC BY 2.0; Tuatara: Public Domain
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