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Chapter 41
Reptiles
Table of Contents
Section 1 Origin and Evolution of Reptiles
Section 2 Characteristics of Reptiles
Section 3 Modern Reptiles
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Chapter 41
Section 1 Origin and Evolution of
Reptiles
Objectives
• Summarize the factors that led to the rise of reptiles as the
dominant land vertebrates.
• Identify three factors that contributed to the success of
dinosaurs.
• Compare two hypotheses to explain the extinction of the
dinosaurs.
• Identify examples of the four modern orders of reptiles.
• Describe three characteristics of modern reptiles that make
them well adapted to life on land.
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Chapter 41
Section 1 Origin and Evolution of
Reptiles
History of Reptiles
Pangaea (the supercontinent formed by the joining
of all of Earth’s land masses) had a drier interior
climate than the coastal regions. Reptiles were
well suited to dry climates.
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Chapter 41
Section 1 Origin and Evolution of
Reptiles
History of Reptiles, continued
The Mesozoic era is often called the Age of Reptiles.
Reptiles flourished due to:
• An abundance of food
• A dry climate
• A mass extinction of other species
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Chapter 41
Section 1 Origin and Evolution of
Reptiles
Continental Drift (Pangaea)
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Chapter 41
Section 1 Origin and Evolution of
Reptiles
Evolution of Dinosaurs
Early in the Mesozoic era, Pangaea started to break
apart.
• The climate of the land masses started to change.
• Some species of reptiles could not adapt and
became extinct.
• Other species flourished.
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Chapter 41
Section 1 Origin and Evolution of
Reptiles
Breakup of Pangaea
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Chapter 41
Section 1 Origin and Evolution of
Reptiles
Evolution of Dinosaurs,
continued
The evolution of reptiles has
been marked by three mass
extinction events, shown to
the right.
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Chapter 41
Section 1 Origin and Evolution of
Reptiles
Evolution of Dinosaurs, continued
Triassic Dinosaurs
• The oldest known dinosaur fossils date from the early
Triassic period, about 235 million years ago.
• These dinosaurs were small and carnivorous.
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Chapter 41
Section 1 Origin and Evolution of
Reptiles
Evolution of Dinosaurs, continued
Several factors contributed to the success of
dinosaurs:
• Legs positioned under the body made them faster
and more agile than other reptiles.
• Dinosaurs were well adapted to dry conditions.
• A mass extinction at the end of the Triassic
period reduced competition.
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Chapter 41
Section 1 Origin and Evolution of
Reptiles
Evolution of Dinosaurs, continued
Jurassic and Cretaceous Dinosaurs
• The Jurassic period is called the golden age of dinosaurs.
• Jurassic dinosaurs included the giant sauropods,
carnivorous theropods, and large herbivores like triceratops.
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Chapter 41
Section 1 Origin and Evolution of
Reptiles
Evolution of Dinosaurs, continued
Dinosaur Diversity
• Dinosaurs were not
limited to terrestrial
habitats.
• Some dinosaurs, such
as pterosaurs, flew.
• Others, such as
ichthyosaurs, inhabited
the oceans.
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Chapter 41
Section 1 Origin and Evolution of
Reptiles
Extinction of Dinosaurs
• Dinosaurs became extinct about 65 million years
ago.
• Evidence suggests that environmental conditions
over many years endangered dinosaur survival.
• Either a single asteroid or multiple asteroid
impacts might have triggered a mass extinction
event that killed the dinosaurs.
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Chapter 41
Section 1 Origin and Evolution of
Reptiles
Mass Extinction
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Chapter 41
Section 1 Origin and Evolution of
Reptiles
Success of Reptiles
There are four modern orders of reptiles:
• Chelonia (turtles and tortoises)
• Crocodilia (alligators and crocodiles)
• Squamata (snakes and lizards)
• Rhynchocephalia (tuataras)
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Chapter 41
Section 1 Origin and Evolution of
Reptiles
Phylogenetic Diagram of
Reptiles, Birds, and Mammals
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Section 1 Origin and Evolution of
Reptiles
Success of Reptiles, continued
Three characteristics contribute to the success of
reptiles on land:
• The amniotic egg
• Watertight skin
• Efficient respiration and excretion
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Section 1 Origin and Evolution of
Reptiles
Success of Reptiles, continued
The amniotic egg:
• contains a large amount of yolk which nourishes
the developing embryo
• is usually surrounded by a leathery or hard shell
within which the embryo develops
• the embryo is surrounded by several membranes
which protect the embryo and exchange gases
and wastes
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Section 1 Origin and Evolution of
Reptiles
Success of Reptiles, continued
Parts of the amniotic egg:
• amnion - the thin membrane including the fluid in which
the embryo floats
• yolk sac - encloses the yolk, the fat-rich food supply for the
developing embryo
• allantois - stores the nitrogenous wastes produced by the
embryo
• chorion - surrounds all other membranes and helps protect
the developing embryo
• albumen - fluid containing protein and water needed by
the embryo
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Chapter 41
Section 1 Origin and Evolution of
Reptiles
Amniotic Egg
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Chapter 41
Section 1 Origin and Evolution of
Reptiles
Parts of an Amniotic Egg
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Chapter 41
Section 1 Origin and Evolution of
Reptiles
Success of Reptiles, continued
Watertight skin
• Amphibians are able to exchange gases and water
through their skin. As a result, they risk dehydration
through evaporation and must live in moist
environments.
• Reptiles have thick, dry, scaly skin that prevents water
loss. As a result, they are able to live in dry
environments.
• The scaly covering of reptile skin is made of keratin, a
tough fibrous protein that makes up scales, hair, and
fingernails.
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Chapter 41
Section 1 Origin and Evolution of
Reptiles
Comparing Amphibian and Reptile Skin
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Chapter 41
Section 1 Origin and Evolution of
Reptiles
Success of Reptiles, continued
Respiration and excretion
• Modern reptiles have developed efficient respiratory
and excretory systems that help them conserve
water.
• Respiratory organs (lungs) located inside the body
reduce water loss through evaporation.
• Nitrogenous wastes secreted in the form of uric
acid, which requires little water for dilution, allows
reptiles to lose only small amounts of water in
their urine.
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Chapter 41
Section 1 Origin and Evolution of
Reptiles
Key Features of Reptiles
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Chapter 41
Section 1 Origin and Evolution of
Reptiles
Characteristics of Reptiles
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Chapter 41
Section 2 Characteristics of
Reptiles
Objectives
• Identify advantages associated with the structure of a
reptile’s heart.
• Describe the respiratory system of reptiles.
• Describe four methods reptiles use to sense their
environment.
• Explain how reptiles regulate their body temperature.
• Compare oviparity, ovoviviparity, and viviparity as
reproductive strategies.
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Chapter 41
Section 2 Characteristics of
Reptiles
Circulatory System
The reptile circulatory system consists of two
loops:
•
Pulmonary loop - carries blood from the heart to
the lungs and then back to the heart
•
Systemic loop - carries blood from the heart to
the body and then back to the heart
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Chapter 41
Section 2 Characteristics of
Reptiles
Circulatory System, continued
• Most reptiles have a three-chambered heart.
• The single ventricle is partially divided by a wall
of tissue called a septum.
• Reptiles can divert blood from the lungs to
conserve energy and warm their bodies.
• Crocodiles have a four-chambered heart.
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Chapter 41
Section 2 Characteristics of
Reptiles
Turtle Heart
Structure
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Chapter 41
Section 2 Characteristics of
Reptiles
Reptile Heart
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Chapter 41
Section 2 Characteristics of
Reptiles
Respiratory System
• The lungs of reptiles are large, and the lining may
be folded into numerous small sacs called alveoli
that increase the internal surface area.
• Reptiles inflate their lungs by expanding their
ribs. This lowers pressure in the chest cavity and
draws air in.
• When the ribs relax, air is forced out.
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Chapter 41
Section 2 Characteristics of
Reptiles
Alveolus/Alveoli
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Chapter 41
Section 2 Characteristics of
Reptiles
Nervous System
• A reptile’s brain has a large cerebrum, a welldeveloped olfactory lobe, and large optic lobes.
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Chapter 41
Section 2 Characteristics of
Reptiles
Nervous System
Reptile senses:
• Sight - Reptiles have large, well-developed eyes.
• Hearing - Sound waves strike the tympanum (eardrum) and
are transmitted by the columella to the inner ear.
• Vibrations - Snakes lack a tympanum and can sense only
low-frequency sounds and ground vibrations.
• Smell - Smell is important for most reptiles. Snakes have a
special structure called the Jacobson’s organ, located in
the roof of the mouth, that also detects odors.
• Heat detection - Pit vipers have a heat-sensitive pit below
each eye that detects prey.
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Chapter 41
Section 2 Characteristics of
Reptiles
Thermoregulation
• The control of body temperature is called
thermoregulation.
• All living reptiles are ectotherms. Ectotherms
warm their bodies by absorbing heat from their
environment.
• Endotherms generate heat internally to maintain
their body temperature.
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Chapter 41
Section 2 Characteristics of
Reptiles
Thermoregulation, continued
Advantages and limitations of ectothermy:
• Ectotherms have a slow metabolism and require
very little energy. They need about one-tenth as
much food as an endotherm of the same size.
• Ectotherms cannot live in very cold climates.
• Ectothermic metabolism cannot provide enough
energy for sustained exertion.
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Chapter 41
Section 2 Characteristics of
Reptiles
Changes in Lizard Body Temperature
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Chapter 41
Section 2 Characteristics of
Reptiles
Comparing Endotherms and Ectotherms
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Chapter 41
Section 2 Characteristics of
Reptiles
Reproduction and Parental Care
There are three patterns of reproduction among
reptiles:
• Oviparity - Eggs are laid in a tough protective
shell.
• Ovoviviparity - Eggs have shells but develop
within the female’s body.
• Viviparity - Eggs have no shells, develop within
the female’s body, and are nourished through a
structure called the placenta.
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Chapter 41
Section 2 Characteristics of
Reptiles
Reproduction and Parental Care, continued
• Many species of reptiles provide no parental care
for their young.
• Some species of lizards and snakes guard and
warm the eggs until they hatch.
• Crocodiles and alligators provide the most
parental care of any reptile. They build a nest,
guard the nest, and carry the hatched young to
the water. A mother crocodile may protect her
young for a year or more.
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Chapter 41
Section 2 Characteristics of
Reptiles
External Structures of a
Timber Rattlesnake
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Chapter 41
Section 2 Characteristics of
Reptiles
Internal Structures of a
Timber Rattlesnake
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Chapter 41
Section 3 Modern Reptiles
Objectives
• Compare the anatomy of turtles with that of other
reptiles.
• Describe the structure that allows crocodilians to
swallow prey under water.
• Explain three antipredator defenses of lizards.
• Describe two ways snakes subdue their prey.
• Identify two reasons that tuataras are rarely seen.
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Chapter 41
Section 3 Modern Reptiles
Order Chelonia
• Chelonia includes turtles and tortoises.
• Turtles generally refers to chelonians that live in water.
• Tortoises generally refers to chelonians that live on land.
• Turtles and tortoises have a shell made out of bony plates.
• The carapace is the top part of the shell. The plastron is the
lower part of the shell.
• The vertebrae and ribs are fused to the interior surface of
the carapace.
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Chapter 41
Section 3 Modern Reptiles
Characteristics of Turtles
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Chapter 41
Section 3 Modern Reptiles
Carapace and Plastron
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Chapter 41
Section 3 Modern Reptiles
Order Crocodilia
• Crocodilians are large, aquatic or semiaquatic
carnivores.
• Order includes crocodiles, alligators, caimans,
and gavials.
• A valve in the oral cavity covers the esophagus
and windpipe, allowing crocodilians to capture
and swallow prey underwater.
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Chapter 41
Section 3 Modern Reptiles
Characteristics of Crocodiles and Alligators
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Chapter 41
Section 3 Modern Reptiles
Order Squamata
Lizards
• Most lizards rely on speed, agility, and
camouflage to elude predators.
• Some lizards can detach their tail to distract
predators. This ability is called autotomy.
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Section 3 Modern Reptiles
Order Squamata, continued
Snakes
• Some snakes kill their prey by wrapping their
body around the prey and suffocating it. This is
called constriction.
• Other snakes kill their prey by injecting venom.
• Prey must be swallowed whole. A snake’s jaw and
skull are joined by a ligament that allows the
snake’s head to stretch around its prey.
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Section 3 Modern Reptiles
Order Squamata, continued
Snakes can inject venom in three different ways:
• Snakes may have grooved fangs at the back of
the mouth that guide poison into puncture.
• Elapid snakes inject poison through two small,
fixed fangs in the front of the mouth.
• Vipers inject venom through large, hinged fangs
in the front of the mouth.
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Chapter 41
Section 3 Modern Reptiles
Characteristics of Snakes and Lizards
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Chapter 41
Section 3 Modern Reptiles
Anatomy of a Snake
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Chapter 41
Section 3 Modern Reptiles
Order Rhynchocephalia
• The order Rhynchocephalia contains only the
tuataras, iguana-like reptiles with a spiny crest
down their backs.
• Tuataras hide in burrows during the day and feed
at night.
• The arrival of humans and new predators in New
Zealand has reduced the number of tuataras.
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Chapter 41
Section 3 Modern Reptiles
Types of Reptiles
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Chapter 41
Standardized Test Prep
Multiple Choice
1. Which is an adaptation that made reptiles the
dominant species in the Mesozoic era?
A. They were endotherms.
B. They could live in Antarctica.
C. They were all large predators.
D. They were well adapted to dry areas.
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Standardized Test Prep
Multiple Choice
1. Which is an adaptation that made reptiles the
dominant species in the Mesozoic era?
A. They were endotherms.
B. They could live in Antarctica.
C. They were all large predators.
D. They were well adapted to dry areas.
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Standardized Test Prep
Multiple Choice, continued
2. What are the two basic parts of a turtle’s shell?
F. septum and amnion
G. chorion and allantois
H. keratin and columella
J. carapace and plastron
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Multiple Choice, continued
2. What are the two basic parts of a turtle’s shell?
F. septum and amnion
G. chorion and allantois
H. keratin and columella
J. carapace and plastron
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Multiple Choice, continued
3. What is the purpose of a lizard’s ability to lose its tail
and grow a new one?
A. to capture prey
B. to hide from predators
C. to escape from predators
D. to reduce its need for food
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Multiple Choice, continued
3. What is the purpose of a lizard’s ability to lose its tail
and grow a new one?
A. to capture prey
B. to hide from predators
C. to escape from predators
D. to reduce its need for food
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Multiple Choice, continued
4. Long legless bodies may have arisen as an
adaptation that helped snakes do what?
F. catch prey
G. swallow large animals
H. absorb oxygen through their skin
J. burrow and move through thick vegetation
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Multiple Choice, continued
4. Long legless bodies may have arisen as an
adaptation that helped snakes do what?
F. catch prey
G. swallow large animals
H. absorb oxygen through their skin
J. burrow and move through thick vegetation
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Multiple Choice, continued
The graph below shows changes in air temperature and
changes in the body temperature of a lizard. Use the
graph below to answer the question that follows.
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Multiple Choice, continued
5. In order for the lizard to raise its internal temperature
it must do which of the following?
A. rest in the shade
B. bask in sunshine
C. increase its internal temperature through activity
D. decrease its internal temperature through activity
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Multiple Choice, continued
5. In order for the lizard to raise its internal temperature
it must do which of the following?
A. rest in the shade
B. bask in sunshine
C. increase its internal temperature through activity
D. decrease its internal temperature through activity
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Multiple Choice, continued
6. Ectotherm : reptiles :: endotherm
F. fishes
G. insects
H. mammals
J. amphibians
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Multiple Choice, continued
6. Ectotherm : reptiles :: endotherm
F. fishes
G. insects
H. mammals
J. amphibians
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Multiple Choice, continued
The illustration below shows a cross section of a turtle’s
heart. Use the illustration to answer the question that
follows.
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Multiple Choice, continued
7. Which feature of a turtle’s heart structure is different
from that of a crocodile’s?
A. 1
B. 2
C. 3
D. 4
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Multiple Choice, continued
7. Which feature of a turtle’s heart structure is different
from that of a crocodile’s?
A. 1
B. 2
C. 3
D. 4
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Standardized Test Prep
Short Response
A reptile can redirect blood flow through the heart to
send some deoxygenated blood back to the body
instead of to the lungs.
What is the advantage to the lizard of redirecting
blood flow in this manner?
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Short Response, continued
A reptile can redirect blood flow through the heart to
send some deoxygenated blood back to the body
instead of to the lungs.
What is the advantage to the lizard of redirecting
blood flow in this manner?
Answer: By redirecting warmed blood from the skin
back to the body, for example, a lizard can heat
his body much more quickly.
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Chapter 41
Standardized Test Prep
Extended Response
Base your answers to parts A & B on the information below.
There are three patterns of reproduction among reptiles. They
differ in how long eggs remain in the female and how the
developing young are provided with nutrition.
Part A With these differences in mind, compare oviparity,
ovoviviparity, and viviparity.
Part B In which pattern of reproduction is a placenta present?
Explain the function of the placenta.
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Extended Response, continued
Answer:
Part A Oviparous animals lay eggs. In viviparity
young are born without shells. Reptiles whose
eggs hatch inside their bodies or shortly after
being laid exhibit ovoviviparity.
Part B The placenta is present in viviparity. It is a
highly vascularized structure that provides a
link for the diffusion of nutrients and gases
between the mother and embryo.
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