31-1 Reptiles
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31-1 Reptiles
What Is a Reptile?
What Is a Reptile?
A reptile is a vertebrate that has dry, scaly skin, lungs,
and terrestrial eggs with several membranes.
These characteristics enable reptiles to live their entire
lives out of water.
Reptilian skin is dry and covered with thick, protective
scales.
Scales may be rough or smooth and prevent the loss
of body water in dry environments.
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31-1 Reptiles
What Is a Reptile?
The scaly layer of skin doesn’t grow, so it must be
shed periodically as the reptile increases in size.
Today, reptiles are widely distributed on Earth.
The only places on Earth that most reptiles cannot live
in are very cold areas.
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31-1 Reptiles
Evolution of Reptiles
Evolution of Reptiles
Reptiles were the first vertebrates that were not
dependent on water for reproduction.
The first reptile fossil dates back to the Carboniferous
Period.
Earth’s climate became cooler and less humid.
Lakes and swamps dried up, reducing the available
habitat for water-dependent amphibians.
Then the first great adaptive radiation of reptiles
began.
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31-1 Reptiles
Evolution of Reptiles
Mammal-like Reptiles
Displayed a mix of reptilian and mammalian
characteristics.
These chordates eventually came to dominate
many land habitats.
Toward the end of the Triassic Period, 215 mya,
dinosaurs began to become dominant.
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31-1 Reptiles
Evolution of Reptiles
Dinosaurs
During the late Triassic and Jurassic periods, a great
adaptive radiation of reptiles took place.
The Mesozoic Era is often called the Age of Reptiles.
Two separate groups of large aquatic reptiles swam in
the seas.
Ancestors of modern turtles, crocodiles, lizards, and
snakes populated many land habitats.
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31-1 Reptiles
Evolution of Reptiles
Dinosaur structure and behavior varied:
•
•
•
•
•
Ranged in size from small to enormous.
Ran on two legs or on four legs.
Ate leafy plants or other animals.
Some lived in small family groups and some in
large herds.
Some may have had feathers as a means of
regulating body temperature.
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31-1 Reptiles
Evolution of Reptiles
All of dinosaurs belonged to one of two major groups:
•
•
Ornithischia, or “bird-hipped” dinosaurs
Saurischia, or “lizard-hipped” dinosaurs
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Evolution of Reptiles
At the end of the Cretaceous, a mass extinction
occurred that killed the dinosaurs as well as other
plant and animal groups.
It was caused by a dramatic series of natural
disasters:
• string of massive volcanic eruptions
• lava flows
• dropping of sea level
• impact of huge asteroid or comet into the Yucatan
Peninsula in Mexico
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31-1 Reptiles
Form and Function in Reptiles
Form and Function in Reptiles
Tough, scaly skin and the ability to control body
temperature are two adaptations to terrestrial life.
Adaptations that have contributed to the success of
reptiles on land are:
•well-developed lungs
•a double-loop circulatory system
•a water-conserving excretory system
•strong limbs
•internal fertilization
•shelled, terrestrial eggs
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Form and Function in Reptiles
Body Temperature Control
Reptiles are ectotherms.
Ectotherms are animals that rely on behavior to
control body temperature.
To warm up, they bask in the sun or stay under water
at night.
To cool down, they move to the shade or take shelter
in underground burrows.
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31-1 Reptiles
Form and Function in Reptiles
Feeding
Reptiles eat a wide range of foods.
• Iguanas eat plants.
• Snakes eat small animals, bird eggs, or other
snakes.
• Crocodiles and alligators eat fish and land
animals.
• Most eat insects, such as the chameleon
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Form and Function in Reptiles
Respiration
Reptile lungs are spongy, allowing for a larger area
of gas-exchange.
Many reptiles have muscles around the ribs that
expand and collapse the chest cavity.
Most reptiles have two lungs, but certain species of
snakes have just one lung.
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31-1 Reptiles
Form and Function in Reptiles
Circulation
Reptiles have a double-loop circulatory system:
• One loop brings blood to and from the lungs.
• One loop brings blood to and from the rest of
the body.
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Form and Function in Reptiles
Reptile hearts have two atria and either one or two
ventricles.
•
Most reptiles have one ventricle with a partial
septum, or wall, that separates oxygen-rich and
oxygen-poor blood.
•
Crocodiles and alligators have two atria and two
ventricles.
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Form and Function in Reptiles
To
body
Right
atrium
From
lungs
To
lungs
Left atrium
From
body
Incomplete division
Ventricle
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31-1 Reptiles
Form and Function in Reptiles
Excretion
Urine is produced in the kidneys.
• In some reptiles, urine flows in tubes directly
into a cloaca.
• In others, a bladder stores urine before it is
expelled.
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Form and Function in Reptiles
Reptiles that live mainly in water excrete most of their
nitrogenous wastes as ammonia.
Other reptiles that live mainly on land convert
ammonia into uric acid.
•
•
Uric acid is much less toxic than ammonia.
•
By eliminating solid wastes, a reptile can
conserve water.
In the cloaca, urine is reduced to crystals of uric
acid that form a pasty white solid.
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Form and Function in Reptiles
Response
Reptilian brains are similar to amphibians.
Their cerebrum and cerebellum are more developed
than other parts of the brain.
Reptiles that are active in the day have complex eyes
and see color well.
Many snakes also have an extremely good sense of
smell.
Most reptiles have a pair of nostrils and sensory
organs in the roof of the mouth that detect chemicals
when reptiles flick their tongues.
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Form and Function in Reptiles
Reptiles have simple ears with an external eardrum
and a single bone that conducts sound to the inner
ear.
Snakes can also pick up vibrations in the ground
through bones in their skulls.
Some snakes can detect the body heat of their prey.
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Form and Function in Reptiles
Movement
Reptiles with legs have large strong limbs that enable
them to walk, run, burrow, swim, or climb.
Some have legs that are rotated further under the
body, enabling them to carry more body weight.
The legs and feet of many aquatic turtles have
developed into flippers.
Reptiles’ backbones help accomplish much of their
movement.
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Form and Function in Reptiles
Reproduction
All reptiles reproduce by internal fertilization, in which
the male deposits sperm inside the female’s cloaca.
Most reptiles are oviparous, laying eggs that develop
outside the mother’s body.
After fertilization, the female’s reproductive system
covers the embryo with several membranes and a
leathery shell.
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31-1 Reptiles
Form and Function in Reptiles
The shell and membranes protect the embryo and
prevent the egg from drying out.
This type of egg, an amniotic egg, is one of the most
important adaptations to life on land.
An amniotic egg has four membranes—the amnion,
the yolk sac, the chorion, and the allantois.
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31-1 Reptiles
Form and Function in Reptiles
The amnion is a fluid-filled sac that surrounds and
cushions the developing embryo.
Amnion
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Form and Function in Reptiles
The chorion regulates the transport of oxygen and
carbon dioxide between the surface of the egg and
the embryo.
Chorion
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Form and Function in Reptiles
The yolk sac contains the yolk that serves as a
nutrient-rich food supply for the embryo.
Yolk sac
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31-1 Reptiles
Form and Function in Reptiles
The allantois stores the waste produced by the
embryo.
Allantois
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31-1 Reptiles
Groups of Reptiles
Groups of Reptiles
The four surviving groups of reptiles are:
• lizards and snakes
• crocodilians
• turtles and tortoises
• tuatara
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31-1 Reptiles
Groups of Reptiles
Lizards
Modern lizards and snakes belong to the order
Squamata.
Most lizards have four legs and clawed toes, external
ears and movable eyelids.
Some lizards have evolved into highly specialized
forms.
For example, Gila monsters, large, stocky lizards of
the SW United States, have glands in the lower jaw
that produce venom for defense against predators.
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31-1 Reptiles
Groups of Reptiles
Snakes
Snakes have no legs.
They range in size beginning as small as an
earthworm up to an 8 meter long python.
They ability of snakes to produce venom has caused
some people to harbor unjustified fear of all snakes.
More people die from bee stings than snake bites.
Snakes have immovable eyelids and no external ear
openings.
Snakes are very efficient predators.
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Groups of Reptiles
Crocodilians
Order Crocodilia: alligators, crocodiles, caimans and
gavials
Crocodilians have long, broad snouts and a squat
appearance.
They are fierce carnivores and prey on animals such
as fishes, deer, and even humans.
Females guard their eggs from predators and watch
over their young after the eggs hatch.
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31-1 Reptiles
Evolution of Reptiles
Crocodilians live only where it is warm year-round.
Alligators and caimans live only in fresh water and
are found almost exclusively in North and South
America.
Crocodiles live in either fresh or salt water and are
native to Africa, India, and Southeast Asia.
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Groups of Reptiles
Turtles and Tortoises
Order Testudines
Turtles live in water, tortoises live on land.
A terrapin is a turtle that lives in water that is
somewhat salty.
Turtles and tortoises have a two-part shell built into
the skeleton: a dorsal part, or carapace and a ventral
part, or plastron.
The backbone forms the center of the carapace.
The head, legs, and tail emerge from holes where the
carapace and plastron join.
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Form and Function in Reptiles
Liver
Heart
Kidney
Cloaca
Bladder
Digestive
tract
Lung
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Groups of Reptiles
Tortoises and most turtles pull into their shells for
protection.
Lacking teeth, these reptiles have horny ridges that
cover the upper and lower jaws.
The jaws are often very powerful.
All possess strong limbs that lift their body off the
ground when walking or to propel the body when
swimming.
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31-1 Reptiles
Groups of Reptiles
Tuataras
Order Sphenodonta
Tuataras are the only surviving members of the order
and are found only on a few islands off New Zealand.
They resemble lizards in many ways but they lack
external ears and retain primitive scales.
They have a “third eye,” which is part of a complex
organ located on top of the brain.
This eye can sense the level of sunlight, but its
function is unknown.
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Ecology of Reptiles
Ecology of Reptiles
Many reptiles are in danger because of habitat
destruction.
Humans hunt reptiles for food, for pets, and for their
skins.
Laws protect some species, but more conservation
efforts are needed to counteract their dwindling
numbers.
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