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Reptiles and Birds
Reptiles
Reptiles
What is a reptile?
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A reptile is a vertebrate that has dry,
scaly skin, lungs, and terrestrial
eggs with several membranes.
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These characteristics enable reptiles to
live their entire lives out of water.
What is a reptile?

Reptilian skin is dry and covered with
thick, protective scales.

This prevents the loss of body water in
dry environments.
The scaly layer of skin doesn’t grow,
so it must be shed periodically as the
reptile increases in size.
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Evolution of Reptiles
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Reptiles were the first vertebrates that
were not dependent on water for
reproduction.
The first reptile fossil dates back to the
Carboniferous Period.
Evolution of Reptiles
Dinosaurs
 During the late Triassic and Jurassic
periods, a great adaptive radiation of
reptiles took place.
adaptive radiation – a single species or a small
group of species has evolved into diverse forms that
live in different ways

The Mesozoic Era is often called the Age of
Reptiles.
Triassic Reptiles
Evolution of Reptiles

Dinosaur structure and behavior
varied:
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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.
Some may have had feathers.
Evolution of Reptiles
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All of dinosaurs belonged to one of two
major groups:
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Ornithischia, or “bird-hipped” dinosaurs
Saurischia, or “lizard-hipped” dinosaurs
At the end of the Cretaceous, a mass
extinction occurred that killed the
dinosaurs as well as other plant and
animal groups.
Form and Function: Reptiles

Tough, scaly skin and the ability to
control body temperature are two
adaptations to terrestrial life.
Form and Function: Reptiles

Adaptations that have contributed to
the success of reptiles on land are:
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well-developed lungs
a double-loop circulatory system
a water-conserving excretory system
strong limbs
internal fertilization
shelled, terrestrial eggs
Body Temperature Control

Reptiles are ectotherms.

Ectotherms are animals that rely on
behavior to control body temperature.
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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.
Feeding
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Reptiles eat a wide range of foods.
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Iguanas eat plants.
Snakes eat small animals, bird eggs, or other snakes.
Crocodiles and alligators eat fish and land animals.
Chameleons eat insects.
Respiration
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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.
Circulation

Reptiles have a double-loop circulatory
system:
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One loop brings blood to and from the
lungs.
One loop brings blood to and from the
rest of the body.
Circulation
Liver
Kidney
Cloaca
Bladder
Digestive
tract
Lung
Heart
Circulation

Reptile hearts have two atria and
either one or two ventricles.
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Most reptiles have one ventricle with a
partial septum that separates oxygen-rich
and oxygen-poor blood.
Crocodiles and alligators have two atria
and two ventricles.
Circulation
To
body
Right
atrium
From
lungs
To
lungs
Left atrium
From
body
Incomplete division
Ventricle
Excretion

Urine is produced in the kidneys.
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In some reptiles, urine flows in tubes
directly into a cloaca.
In others, a bladder stores urine before it
is expelled.
Excretion

Other reptiles convert ammonia into
uric acid.
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In the cloaca, urine is reduced to crystals
of uric acid that form a pasty white solid.
By eliminating solid wastes, a reptile can
conserve water.
Response
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Reptilian brains are similar to
amphibians.
Their cerebrum and cerebellum are
more developed than other parts of the
brain.
Response
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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 sensory organs in the
mouth that detect chemicals when
reptiles flick their tongues.
Response
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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.
Movement

Reptiles with legs have large strong
limbs.
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Some have legs that are rotated further
under the body, enabling them to carry
more body weight.
Movement
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The legs and feet of many aquatic
turtles have developed into flippers.

Reptiles’ backbones help accomplish
much of their movement.
Reproduction
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Most reptiles are oviparous, laying eggs
that develop outside the mother’s body.
All reptiles reproduce by internal
fertilization, in which the male deposits
sperm inside the female’s cloaca.
Reproduction

After fertilization, the female’s reproductive
system covers the embryo with several
membranes and a leathery shell.
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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.
The Amniotic Egg
Allantois
Amnion
Chorion
Yolk sac
The Amniotic Egg
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The amnion is a fluid-filled sac that
surrounds and cushions the
developing embryo.
The chorion regulates the transport of
oxygen and carbon dioxide between
the surface of the egg and the embryo.
The Amniotic Egg
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The yolk sac contains the yolk that
serves as a nutrient-rich food supply
for the embryo.
The allantois stores the waste
produced by the embryo.
Groups of Reptiles

The four surviving groups of reptiles
are:
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lizards and snakes
crocodilians
turtles and tortoises
tuatara
Lizards
Lizards and Snakes
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Most lizards have four legs and clawed
toes.
Most lizards have external ears and
movable eyelids.
Some lizards have evolved into highly
specialized forms.
Snakes
Lizards and Snakes
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Snakes have no legs.
Snakes have immovable eyelids and
no external ear openings.
Snakes are efficient predators.
Crocodilians
Crocodilians
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Crocodilians have long, broad snouts
and a squat appearance.
They 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.
Crocodilians
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Crocodilians live only where it is warm yearround.
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.
Turtles and Tortoises
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Turtles live in water.
Tortoises live on land.
A terrapin is a turtle that lives in water
that is somewhat salty.
Turtles and Tortoises
Turtles and Tortoises
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Turtles and tortoises have a two-part
shell built into the skeleton:
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a dorsal part, or carapace
a ventral part, or plastron
The head, legs, and tail emerge from
holes where the carapace and plastron
join.
Tortoises and most turtles pull into their
shells for protection.
Tuataras
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Tuataras are found only on a few
islands off New Zealand.
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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.
Tuataras
Ecology of Reptiles
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Many reptiles are in danger because of
habitat destruction.
Humans hunt reptiles for food, for pets,
and for their skins.
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Laws protect some species, but more
conservation efforts are needed to
counteract their dwindling numbers.