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Reptiles and Birds
• A spur-thighed
tortoise hatches from
its egg, ready to face
life as a young reptile
Reptiles and Birds
Reptiles
• Humans have always been fascinated by—
and sometimes frightened of—reptiles
• Some people fear snakes because of their
venomous bites or the way they crawl
• Explorers' encounters with lizards and crocodiles
inspired images of dragons in European folk
tales
• Turtles, too, are the subject of many a fable
• The truth about reptiles is that they are as
astonishing as any creatures of human
imagination
REPTILES
• First Vertebrates to make the complete
transition to life on land
– Two factors probably lead to this transition
• An increase in competition for food and space
among all the life forms in aquatic environments
• Limited competition for the insects and plants that
could be used as food on land
• Dominated the Earth for 160 million years
• Evolved from amphibians
Iguana
• Like all petiles, this
green ignuana has
lungs and dry, scaly
skin
• These
characteristics help
the iguana live on
land
Iguana
What Is a Reptile?
• The basic body plan of a reptile is
typical of land vertebrates: a welldeveloped skull, a backbone and tail,
two limb girdles, and four limbs
• Two types of reptiles have slightly
different body plans:
– Snakes are mostly limbless
– Turtles have hard shells that are fused to
their vertebrae
What Is a Reptile?
• What characteristics do snakes, turtles,
and other reptiles share?
• 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, unlike
their amphibious relatives
What Is a Reptile?
• Reptilian skin is dry and often covered with
thick, protective scales
– These scales may be smooth or rough
• A reptile's body covering helps prevent the
loss of body water in dry environments
– But dry, waterproof skin can also be a disadvantage
to reptiles
– Because the tough, scaly layer of skin does not
grow when the rest of a reptile grows, it must be
shed periodically as the reptile increases in size
What Is a Reptile?
• Today, reptiles are widely distributed on
Earth
• Temperate and tropical areas contain
populations of reptiles that are remarkably
diverse in appearance and lifestyle
• The only places on Earth that most
reptiles cannot live in are very cold
areas
– The reason for this will soon be apparent.
Evolution of Reptiles
• To colonize dry habitats, animals needed a way to reproduce
that did not require depositing eggs into water
– Reptiles, which evolved from amphibianlike ancestors, were the first
vertebrates to develop this adaptation
• The fossil of the first known reptile dates back to the Carboniferous
Period, some 350 million years ago
• As the Carboniferous Period came to a close and the Permian
Period began, Earth's climate became cooler and less humid
– Many lakes and swamps dried up, reducing the available habitat
for water-dependent amphibians
– Under these drier conditions, the first great adaptive radiation of
reptiles began
– These environmental pressures had a negative impact on the
survival of many amphibian populations
PHYLOGENETIC TREE
LIMBS
REPTILE EVOLUTION
• Arose from a group of ancestral reptiles
(Cotylosaurs) about 310 million years ago
– Resembled lizards with teeth for eating
insects (Insectivores)
– Gave rise to many diverse forms
– Dinosaurs:
• Two groups: based on pelvic structures
– Saurischians: hip structures like modern lizards
– Ornithischians: hip structures similar to modern birds
BRONTOSAURUS:A SAURISCHIAN
IGUANODON: A ORNITHISCHIAN
REPTILIAN EVOLUTION
Mammal-like Reptiles
• By the end of the Permian Period, about 245 million
years ago, a great variety of reptiles roamed Earth
• One early group was the mammal-like reptiles, which
displayed a mix of reptilian and mammalian
characteristics
• These chordates eventually came to dominate many
land habitats
• Toward the end of the Triassic Period, about 215
million years ago, another group of reptiles that had
remained in the background for millions of years—
the dinosaurs—became dominant
THECODONT
Enter the Dinosaurs
•
During the late Triassic and Jurassic
periods, a great adaptive radiation of
reptiles took place
– The vast diversity and abundance of
reptiles during that time are the main
reasons why 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
• And dinosaurs were everywhere
– The figure two dinosaurs,
Plateosauras and
Coelophysis
– The illustration also shows
another kind of reptile,
Teratosaurus
» In the Triassic Period,
reptiles such as these
lived in the forests
Triassic Reptiles
• The herbivorous Plateosaurus
(left), nibbling on leaves, was a
dinosaur, as were the group
of carnivorous Coelophysis
(center)
• The large carnivorous
Teratosaurus (right) was a
reptile but not a dinosaur
• What characteristics did these
reptiles have in common with
modern reptiles?
Triassic Reptiles
Enter the Dinosaurs
•
•
•
•
•
Dinosaurs ranged in size from small to enormous
They ran on two legs or lumbered along on four
Some, like Plateosaurus, ate leafy plants
Coelophysis and other hunters traveled in herds
Others, such as duckbilled Maiasaura, lived in small family groups,
caring for their eggs and young in carefully constructed nests
• Certain dinosaurs may even have had feathers, which may have
evolved as a means of regulating body temperature
• All of the dinosaurs, however, belonged to one of two major
groups:
– Ornithischia, or “bird-hipped” dinosaurs
– Saurischia, or “lizard-hipped” dinosaurs
• From one of these two branches of dinosaurs, probably the Saurischia,
came the earliest members of evolutionary lines that would lead to
modern birds
Exit the Dinosaurs
• At the end of the Cretaceous Period, about 65 million
years ago, a mass extinction occurred worldwide
• This extinction was caused by a dramatic series of
natural disasters
– These disasters probably included a string of massive
volcanic eruptions and lava flows, the dropping of sea level,
and a huge asteroid or comet smashing into what is now the
Yucatán Peninsula in Mexico
• The asteroid or comet collision produced major forest fires and
enormous dust clouds
• After these events, dinosaurs, along with many other
animal and plant groups, became extinct
– The disappearance of these organisms during the late
Cretaceous Period provided opportunities for other kinds of
organisms to evolve on land and in the seas
ICHTHYOSAUR
PLESIOSAUR
PTERANODON
REPTILE ADAPTATIONS
•
Amniote Egg:
– New reproductive structure that evolved allowing reproduction on land
– An egg with a protective membrane and a porous shell enclosing the developing embryo
– Provides an internal aquatic environment that enables the embryo to survive a dry
environment
– Four specialized membranes:
• Amnion:
– Thin membrane enclosing the salty fluid in which the embryo floats
– Acts like a shock absorber and protects the embryo
• Yolk sac:
– Encloses the yolk, a protein-rich food supply for the developing embryo
• Allantois:
– Stores the nitrogenous wastes produced by the embryo until the egg hatches
• Chorion:
– Lines the outer shell and thus encloses the embryo and all the other membranes
– Regulates the exchange of oxygen and carbon dioxide between the egg and the
outside environment
– Surrounded by a leathery shell that may be hard in some species because of the presence of
calcium carbonate
– Waterproof but allows gases to flow between the environment and the chorion
EGG
EGG
Form and Function in Reptiles
• Most reptiles have adapted to a fully terrestrial life
• Tough, scaly skin is one adaptation to this type of life
• Well-developed lungs; a double-loop circulatory
system; a water-conserving excretory system;
strong limbs; internal fertilization; and shelled,
terrestrial eggs are the other adaptations that have
contributed to the success of reptiles on land
• In addition, reptiles can control their body temperature by
moving to a different place
REPTILE ADAPTATION
• Waterproof skin:
– Dry body covering of horny scales or plates
– Scaly covering develops as surface cells filled
with keratin (same protein that forms human
fingernails and bird feathers)
– Prevents water loss and protects reptiles from
wear and tear associated with living in rugged
terrestrial environments
– Some molt periodically
Body Temperature Control
• The ability to control their body temperature is an
enormous asset for active animals
• All the animals that you have read about so far are
ectotherms
• Ectotherms rely on behavior to help control body
temperature
• Turtles, snakes, and other modern reptiles are all
ectotherms
• To warm up, they bask in the sun during the day or
stay under water at night
• To cool down, they move to the shade, go for a
swim, or take shelter in underground burrows
REPTILE ADAPTATIONS
• Temperature regulation:
– Ecothermic (cold blooded): body temperature
is determined by the environment
– Cannot generate and regulate body heat
internally
• Can eat low caloric foods
• Can go for long period without eating
REPTILE ADAPTATIONS
• Limbs have toes with claws
– Snakes rely on their scaly skin and highly developed skeletal
and muscular systems for movement
• Respiration: lungs
• Circulatory System:
– Partially divided ventricle separates the deoxygenated blood
flowing from the body from the oxygenated blood returning from
the lungs
• Alligators and Crocodiles have four separate chambers allowing
total separation of oxygenated and deoxygenated blood
• Excretory System:
– land dwelling reptiles conserve water by excreting nitrogenous
wastes in a dry or pasty form as crystals of uric acid
Feeding
• Reptiles eat a wide range of foods
• Iguanas, which are herbivores, tear plants into shreds and swallow
the tough, fibrous chunks
– Their long digestive systems enable them to break down plant
material
• Many other reptiles are carnivores
– Snakes, for example, prey on small animals, bird eggs, or even other
snakes, grabbing them with their jaws and swallowing them
– Crocodiles and alligators eat fish and even land animals when they can
catch them
• Most reptiles eat insects
• Chameleons have sticky tongues as long as their bodies that flip out
to catch insects
Gaboon Viper
• The gaboon viper, like
all snakes, is entirely
carnivorous
• It eats mice and other
small mammals by
stretching its jaws
wide and swallowing
its prey whole
Gaboon Viper
Respiration
• The lungs of reptiles are spongy, providing more gas-exchange
area than those of amphibians
– This isn't surprising, because most reptiles cannot
exchange gases through their skin the way many moistskinned amphibians do
• Many reptiles have muscles around their ribs that expand the chest
cavity to inhale and collapse the cavity to force air out
• Several species of crocodiles also have flaps of skin that can
separate the mouth from the nasal passages, allowing these
crocodiles to breathe through their nostrils while their mouth remains
open
• To exchange gases with the environment, reptiles have two
efficient lungs or, in the case of certain species of snakes, one
lung
Circulation
• Reptiles have an efficient double-loop circulatory
system
– One of the loops brings blood to and from the lungs, and
the other loop brings blood to and from the rest of the body
• Reptile hearts contain two atria and either one or two
ventricles
– Most reptiles have a single ventricle with a partial septum,
or wall, that helps separate oxygen-rich and oxygen-poor
blood during the pumping cycle
• Crocodiles and alligators, however, have the most
developed hearts of living reptiles
– The heart consists of two atria and two ventricles—an
arrangement that is also found in birds and mammals
CIRCULATORY SYSTEM
Circulation in a Turtle
• The internal organs
of most reptiles
include a threechambered heart
with two atria and
one partially divided
ventricle
• According to the
diagram, how does
blood flow through a
turtle’s heart?
Circulation in a Turtle
Excretion
• Urine is produced in the kidneys
• In some reptiles, urine flows through
tubes directly into a cloaca similar to
that of amphibians
• In others, a urinary bladder stores urine
before it is expelled from the cloaca
Excretion
• Reptiles' urine contains either ammonia or uric acid
• Reptiles that live mainly in water, such as crocodiles and
alligators, excrete most of their nitrogenous wastes in the form
of ammonia, a toxic compound
– Crocodiles and alligators drink a large amount of water, which
dilutes the ammonia in the urine and helps carry it away
• In contrast, many other reptiles—especially those that live
entirely on land—do not excrete ammonia directly
– Instead, they convert ammonia into a compound called uric acid
• Uric acid is much less toxic than ammonia, so it does not have to be
diluted as much
• In these reptiles, excess water is absorbed in the cloaca,
reducing urine to crystals of uric acid that form a pasty white
solid
• By eliminating wastes that contain little water, a reptile can
conserve water
Response
• The basic pattern of a reptile's brain is similar to that of an
amphibian, although the cerebrum and cerebellum are
considerably larger compared to the rest of the brain
• Reptiles that are active during the day tend to have complex
eyes and can see color well
• Many snakes also have an extremely good sense of smell
• In addition to a pair of nostrils, most reptiles have a pair of sensory
organs in the roof of the mouth that can detect chemicals when
the reptiles flick their tongues
• 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, such as a viper, have the extraordinary ability to
detect the body heat of their prey
Movement
• Compared with most amphibians, reptiles with legs
tend to have larger, stronger limbs that enable them
to walk, run, burrow, swim, or climb
• The legs of some reptiles are also rotated further
under the body than those of amphibians, enabling
reptiles to carry more body weight
• The legs and feet of many aquatic turtles have
developed into flippers
• As with amphibians, the backbones of reptiles help
accomplish much of their movement
Reproduction
• All reptiles reproduce by internal fertilization,
in which the male deposits sperm inside the
body of the female
• Most male reptiles have a penislike organ
that allows them to deliver sperm into the
female's cloaca
• After fertilization has occurred, the female's
reproductive system covers the embryos with
several membranes and a leathery shell
Reproduction
• Most reptiles are oviparous, laying eggs that develop
outside the mother's body
• Some species, such as the box turtle, lay their eggs in
carefully prepared nests, then abandon them
• Alligators also lay their eggs in nests, but they guard the
eggs until they hatch, and provide some care after
hatching
• Some snakes and lizards are ovoviviparous, and the
young are born alive
– By carrying her eggs within her body, the female can
protect the eggs and keep them warm
REPTILE ADAPTATIONS
• Internal Fertilization:
– Evolution of the penis (sperm is placed inside the
body of the female)
• Waterproof skin:
– Dry body covering of horny scales or plates
– Scaly covering develops as surface cells filled with
keratin (same protein that forms human fingernails
and bird feathers)
– Prevents water loss and protects reptiles from wear
and tear associated with living in rugged terrestrial
environments
– Some molt periodically
Turtle Laying Eggs
• After a female box turtle
digs a hole in the ground
for her nest, she lays her
eggs, dropping them one
by one and gently
lowering them into the
hole with her hind feet
• When she finishes, she
will cover up her nest and
leave without a backward
glance
Turtle Laying Eggs
Amniotic Egg
• Unlike an amphibian egg, which almost always
needs to develop in water, the shell and membranes
of a reptilian egg create a protected environment in
which the embryo can develop without drying out
• This type of egg is called an amniotic egg, named after
the amnion, one of the four membranes that
surrounds the developing embryo
• The other three membranes are the yolk sac, the
chorion, and the allantois
• The amniotic egg, also seen in birds, is one of the
most important adaptations to life on land
Amniotic Egg
• An amniotic egg contains
several membranes and an
external shell
• Although it is waterproof,
the egg shell is porous,
allowing gases to pass
through
• The shell of reptile eggs is
usually soft and leathery
• The amniotic egg is one of the
most important adaptations to
life on dry land
Amniotic Egg
Groups of Reptiles
• Since the dinosaurs disappeared, modern
reptiles have had plenty of time and space
to diversify
• The four surviving groups of reptiles
are:
– Lizards and snakes
– Crocodilians
– Turtles and tortoises
– Tuatara
CLASSIFICATION
• Class: Reptilia
– Order: Rhynchocephalia
– Order: Chelonia
– Order: Crocodilia
– Order: Squamata
ORDER SQUAMATA
•
•
•
•
•
5,640 Species of snakes and lizards
Upper jaw loosely joined to the skull
Paired reproductive organs in male
More structurally diverse than other Orders
Lizards:
– Limbs (a few species are limbless)
– Only two species are venomous (Gila monster of
southwest US and beaded lizard of western Mexico)
Lizards and Snakes
• Modern lizards and snakes belong to the
order Squamata, or scaly reptiles
• Most lizards have legs, clawed toes, external
ears, and movable eyelids
• Some lizards have evolved into highly
specialized forms
• For example, Gila monsters—large, stocky
lizards that live in the southwestern United
States and Mexico—have glands in the lower
jaw that produce venom for defense against
predators
LIZARD: GECKO
GECKO
LIZARD: IGUANA
LIZARD: IGUANA
LIZARD: GILA MONSTER
CHAMELEON
LIZARD: SKINK
ORDER SQUAMATA
• Snakes:
– Evolved from lizards
– Many vertebrae with attached ribs provide framework for muscle
attachment
• Muscles manipulate the skeleton and the skin
• Interaction of bones, muscles, and skin enables a snake to move
– Feeding:
• Most poor vision and hearing
• Sense of smell is highly developed
– Forked tongue gathers chemical from the environment
» Tongue transfers the chemicals to two pits in the roof of the mouth
(Jacobson’s Organ: nerves highly sensitive to chemicals)
» Can stalk prey by following a chemical trail
– Killing:
• Small prey just swallow
• Some constriction
• Some venom (rear fanged, elapids (small fanged like hypodermic needles),
vipers (hinged fangs that swing forward)
Lizards and Snakes
• Snakes have lost both pairs of legs during the
course of their evolution
• Although they are legless, snakes are highly efficient
predators, even in the ocean
• Some snakes are so small that they resemble
earthworms
• Others, such as some species of python, can grow to
more than 8 meters in length
• The ability of certain snakes to produce venom has
caused some people to harbor an unjustified fear of
all snakes
– More people in the United States die from bee stings than
from snakebites
• In fact, snakes tend to avoid people, not confront
them!
SNAKE MOUTH
SNAKE FANGS
SNAKE VERTEBRAE
MOVEMENT
SNAKE: INTERNAL ANATOMY
SNAKE: INTERNAL ANATOMY
SNAKE
SNAKE
ORDER SQUAMATA
• Snakes:
– Swallowing:
•
•
•
•
Small mouths
Can unhinge the jaws allowing the mouth to open extremely wide
Swallow animal whole
Saliva initiates digestion
– Defense:
• Camouflage, change body shape, or sound (hiss)
– Reproduction:
• Most are oviparous: female lays eggs that hatch outside body
• Some are ovoviviparous:
– Female carries the eggs in her body throughout development
– Eggs hatching inside her
– The young are born live
SNAKE JAW AND SWALLOWING
Diversity of Reptiles
• The four orders of living
reptiles are:
–
–
–
–
Squamata
Crocodilia
Testudines
Sphenodonta
• The common names of
these modern reptile
groups are lizards and
snakes, crocodilians,
turtles and tortoises, and
the tuatara
Diversity of Reptiles
ORDER CROCODILIA
•
•
•
•
•
•
•
•
•
•
•
•
•
23 species
Crocodiles, alligators, caimans, and gavials
Many species have remained unchanged for 200 million years
All live in or near water
Largely nocturnal
All are carnivorous
Valve in back of the mouth prevents water from entering the air passage when
feeding under water
Heart: 4 chambered
Parental care in some species
Crocodiles:
– Africa, Asia, Americas, South Florida
Alligators:
– China, Southern USA
Caimans:
– Central America and becoming established in Florida
Gavials:
– India, Burma
Crocodilians
• Any member of the order Crocodilia—including
alligators, crocodiles, caimans, and gavials—can easily
be recognized by its long and typically broad snout
and its squat appearance
• Crocodilians are fierce carnivores that prey on animals
such as fishes, deer, and even humans
• Crocodilians are very protective of their young
• The females guard their eggs from predators
• After the eggs are hatched, the mother gently carries her
young to a nursery area and watches over them
Crocodilians
• Crocodilians live only in the tropics and
subtropics, where the climate remains warm
year-round
• Alligators, and their relatives the caimans, live
only in fresh water and are found almost
exclusively in North and South America
• Crocodiles, on the other hand, may live in either
fresh or salt water and are native to Africa, India,
and Southeast Asia
ORDER CROCODILIA
CROCODILE: SNOUT LONG AND TAPERED
ALLIGATOR: SNOUT ROUNDED
ORDER CHELONIA
• 265 species of turtles and tortoises
– Turtles: aquatic
• Must return to land to lay their eggs
• Freshwater: terrapins
– Tortoises: terrestrial
• Evolutionary stability
• Shell: hard plates or tough leathery skin
– Carapace: dorsal
• In most species, fused with vertebrae and ribs
– Plastron: ventral
Turtles and Tortoises
• Turtles and tortoises are members of
the order Testudines
• The name turtle usually refers to
members of this order that live in water;
the name tortoise refers to those that
live on land
• A terrapin is a turtle that is found in
water that is somewhat salty
Turtles and Tortoises
• Turtles and tortoises have a shell built into
the skeleton, although in a few species the
shell is not very hard
• The shell consists of two parts: a dorsal part, or
carapace, and a ventral part, or plastron
– The animal's backbone forms the center of the
carapace
• The head, legs, and tail stick out through holes
where the carapace and plastron join
• Tortoises and most turtles pull into their shells to
protect themselves
Turtles and Tortoises
• Several other adaptations allow turtles and
tortoises to live in a wide range of habitats—dry,
wet, and in-between
• Lacking teeth, these reptiles have horny ridges
that cover the upper and lower jaws
– The jaws are often powerful enough to deliver a
damaging bite
• All possess strong limbs that lift their body off
the ground when walking or, in the case of sea
turtles, to drag themselves across a sandy shore
to lay eggs
Tuataras
• The tuatara is the only surviving member of the
order Sphenodonta
– It is found only on a few small islands off the
coast of New Zealand
• Tuataras resemble lizards, but they differ from lizards in
many ways
• For example, they lack external ears and retain
primitive scales
• Tuataras also have a legendary “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
SEA TURTLE
CARAPACE STREAMLINED
SEA TURTLE
CARAPACE STREAMLINED
DOMED CARAPACE
GALAPAGOS TORTOISE
Ecology of Reptiles
• Many reptiles are in danger because their habitats have been,
and are being, destroyed
• In addition, humans hunt reptiles for food, to sell as pets, and for
their skins, from which bags, boots, and combs are made
• Laws now protect some species, such as sea turtles, which were
once numerous in both the Atlantic and Pacific oceans
• Sea turtle recovery programs give many young turtles a head start
on survival
• Although there are many other programs in place that protect
reptiles, more conservation efforts are needed worldwide to
counteract their dwindling numbers
ORDER RHYNCHOCEPHALIA
•
•
•
•
Ancient Order
One species tuatara
Islands off coast of New Zealand
Third eye ( parietal eye) that seems to
function as a thermostat
• Nocturnal (rare for reptiles)
TUATARA
TUATARA
Birds
• Whether they are greeting the dawn with
song or coloring the air with brilliant
feathers, birds are among the most
obvious and welcome of all animals
• From common robins to the spectacular
and rare quetzal of Central America, the
nearly 10,000 modern bird species seem
to live everywhere
What Is a Bird?
• In a group this diverse, it is difficult to find many
characteristics that are shared by all members.
But we can identify the features that most birds
have in common
• Birds are reptilelike animals that maintain a
constant internal body temperature. They
have an outer covering of feathers; two legs
that are covered with scales and are used for
walking or perching; and front limbs
modified into wings
• Most of these features are adaptations for flight
What Is a Bird?
•
•
•
•
•
The single most important
characteristic that separates birds
from living reptiles, and from all
other living animals, is feathers
Feathers are made mostly of protein
and develop from pits in the birds'
skin
Feathers help birds fly and also
keep them warm
The figure at right shows the two
main types of feathers:
– Contour feathers
– Down
Herons and some other birds that live
on or in water also have powder down,
which releases a fine powder that
repels water
Feathers
• Birds have different
types of feathers that
vary in structure and
function
• An outer covering of
feathers is the main
characteristic that
sets birds apart from
other animals
BIRDS
• Adapted for flight (most are capable of flight)
– Body covered with feathers: aerofoil, insulation
– Bones thin and hollow with cross struts reduces weight
– Limbs:
• Most the forelimbs function as wings
• Hindlimbs, with toes, support the body
– Toothless, horny beak
– Endothermic: warm blooded ( body temperature 400 C to 450 C)
• Body heat is generated and regulated internally
– Four chambered heart has a single right aortic arch
– Amniote eggs are encased in hard, calcium containing shells
– Most species incubate eggs in a nest
CLASSIFICATION
• Class: Aves
– Orders: 27
– Species: 9,000
Feathers
• Birds have different
types of feathers that
vary in structure and
function
• An outer covering of
feathers is the main
characteristic that
sets birds apart from
other animals
Feathers
Evolution of Birds
• Paleontologists agree that birds evolved from extinct
reptiles
• Evidence for this hypothesis is provided by many
embryological, anatomical, and physiological
characteristics shared by modern birds and living reptiles
• For example, the embryos of birds and reptiles develop
within amniotic eggs
• Birds, like most reptiles, excrete nitrogenous wastes in
the form of uric acid
• The bones that support the front and hind limbs, and
several other parts of the skeleton, are similar in both
groups
Evolution of Birds
• Most paleontologists think that birds evolved directly from
dinosaurs
• Part of the evidence consists of Archaeopteryx, the first birdlike
fossil discovered
• This fossil dates from the late Jurassic Period, about 150 million
years ago
• Archaeopteryx looked so much like a small, running dinosaur
that it would be classified as a dinosaur except for one
important feature: It had well-developed feathers covering most
of its body
– Those feathers led to the classification of Archaeopteryx as an
early bird
– Unlike modern birds, however, this creature had teeth in its beak, a
bony tail, and toes and claws on its wings
– Thus, Archaeopteryx can be seen as a transitional species with
characteristics of both dinosaurs and birds
Evolution of Birds
• However, other fossil evidence leads some
researchers to hypothesize that birds and
dinosaurs both evolved from an earlier
common ancestor
• The origin of birds is still not completely
resolved
• New fossils of ancient birds are being found all
the time
• So watch for new discoveries and discussions
on the subject!
Bird Evolution
• The diagram at the topshows
the evolutionary tree of modern
birds
• None of the animals shown
are direct ancestors of
modern birds
• But fossils such as
Archaeopteryx (above) do
show a mixture of
characteristics of birds and
dinosaurs
• Based on the diagram, what
are the two alternative
explanations for the evolution
of modern birds?
EVOLUTION
• Evolved from reptiles
– Archaeopteryx: shows link between reptiles and birds
• 150 million years old
• Reptile characteristics:
–
–
–
–
Large skull with teeth
Solid bones
Claws on forelimbs
Long tail
• Bird characteristics:
– Feathers
– Furculum: fused collarbones (wishbone)
• Probably a glider
ARCHAEOPTERYX
ARCHAEOPTERYX
Bird Evolution
• The diagram at the topshows
the evolutionary tree of modern
birds
• None of the animals shown are
direct ancestors of modern
birds
• But fossils such as
Archaeopteryx (above) do
show a mixture of
characteristics of birds and
dinosaurs
• Based on the diagram, what
are the two alternative
explanations for the evolution
of modern birds?
Bird Evolution
Form, Function, and Flight
• One reason for the evolutionary success of birds
is found in the adaptations that allow them to fly
• Birds have a number of adaptations that
enable them to fly
• These adaptations include highly efficient
digestive, respiratory, and circulatory
systems; aerodynamic feathers and wings;
strong, lightweight bones; and strong chest
muscles
• Most birds have these characteristics, even
though some birds cannot fly
Form, Function, and Flight
• The ways in which birds carry out their life
functions, such as obtaining food and
oxygen, contribute to their ability to fly
• For example, flight requires an
enormous amount of energy, which
birds obtain from the food they eat
• Birds also require energy to maintain
their body temperature
Body Temperature Control
• Unlike reptiles, which must draw body warmth from their
environment, birds can generate their own body heat
• Animals that can generate their own body heat are called
endotherms
• Endotherms, which include birds, mammals, and some other
animals, have a high rate of metabolism compared to ectotherms
such as reptiles
• Recall that metabolism is the sum of chemical and physical
processes that go on inside the body
• Metabolism produces heat
• A bird's feathers insulate its body enough to conserve most of
its metabolic energy, allowing the bird to warm its body more
efficiently
• The body temperature of most birds is about 41°C even on cold
winter days
BIRDS
INTERNAL ANATOMY
• Endothermic:
– Generate and regulate body temperature internally
– Most birds body temperature ranges from 400 C to
450 C
– Enables birds to inhabit both warm and cold climates
– Rapid breathing and the digestion of large quantities
of high caloric foods produce the high metabolic rate
necessary to generate heat
• Must eat constantly
– Insulation:
• Feather
• Thin layer of fat (aquatic birds)
BIRDS
EXTERNAL ANATOMY
•
Feathers:
– Modified scales of keratin
– Aerofoil
– Insulation
– Types:
• Down: closest to the body
– Cover the body of young nestling birds
– Insulating undercoat in adults
• Contour:
– Give adult birds a streamline shape for flight
– Coloration
– Additional insulation
• Quill Flight:
– Specialized contour feathers giving lift, balance, and steering capibilities
– Wings and tails
• Filoplumes (pinfeathers):
– Hairlike
• Bristles:
– Dust-filtering bristles near the nostrils
FEATHER
DOWN FEATHER
CONTOUR FEATHERS
QUILL FEATHERS
BIRDS
EXTERNAL ANATOMY
• Feather:
– Structure: combines maximum strength with minimum weight
– Develop from tiny pits in the skin called Follicles
• Shaft develops from the follicle with two vanes on opposite
sides
– Each vane has many branches called barbs (that grow
from the shaft)
» Projections of the Barbs called Barbules have
microscopic hooks that connect and give the feather
its sturdy but flexible shape
– Preen Gland:
• Base of the tail
• Birds use their beaks and rub their feathers with oil from this
gland
– Periodically molt
FEATHER
Feeding
• Any body heat that a bird loses must be
regained by eating food
• The more food a bird eats, the more heat energy
its metabolism can generate
• Because small birds lose heat relatively faster
than large ones, small birds must eat more,
relative to their body size
• In fact, the phrase “eats like a bird” is quite
misleading, because most birds are
voracious eaters!
Feeding
• Birds' beaks, or bills, are adapted to the type of food
they eat
• Insect-eating birds have short, fine bills that can pick
ants and other insects off leaves and branches, or can
catch flying insects
• Seed-eaters have short, thick bills. Carnivorous birds,
such as eagles, shred their prey with strong hooked bills
• Long, thin bills can be used for gathering nectar from
flowers or probing soft mud for worms and shellfish
• Large, long bills help birds to pick fruit from branches,
while long, flat bills are used to grasp fish
BIRDS
EXTERNAL ANATOMY
•
•
•
•
•
•
Beaks:
–
Two nares (nostrils)
–
Toothless
–
Made of keratin various types according to their feeding patterns
• Size and shape are adaptations to the type of food it eats
Feet (hindlimbs):
–
Clawed and covered with keratin
• Typically four toes (3 pointing forward and one pointing backward)
– This arrangement permits easy perching
• Some webbed for swimming
• Some pointed talons for killing
–
Various types based on their life style
• Ability for flight or flightless life style
Wings:
–
Vary greatly in size and shape
• Long wings: long distance fliers
• Short wings: maneuverability
Eyes:
–
Most located on the side of the head
• Both eyes cannot look in the same direction at once
–
Some located at front of head (owls) permitting them to focus on a single object judging its distance
Ears:
–
Located directly behind the eyes
–
Hearing is acute
Smell and Taste: not well developed
BEAKS
FEET
RAPTOR
CARDINAL
BEAK: CRACKING SEEDS
FEET: PERCH
FALCON
BEAK: TEAR FLESH
FEET: TALONS TO GRIP AND KILL
HUMMINGBIRD
BEAK: LONG, THIN FOR NECTAR IN FLOWERS
DUCK
BEAK: FLAT TO SHOVEL MUD
FEET: WEBBED FOR SWIMMING
VULTURE
BEAK: TEARING FLESH
BLUEBIRD
SPOONBILL
OSTRICH
PUFFINS
Feeding
• Birds lack teeth, and therefore they
cannot break down food by chewing it
• However, many birds have specialized
structures to help digest food
• One such structure is the crop, which is
located at the lower end of the esophagus
• Food is stored and moistened in the
crop before it moves further in the
digestive tract
BIRDS
INTERNAL ANATOMY
•
Digestive System:
– Quick and efficient
– Crop:
• Enlargement at the base of the esophagus
• Stores and moistens food
– Stomach: two parts
• Proventriculus:
– Gastric juices begin breaking down the food
• Gizzard:
– Muscular organ that kneads and crushes the food
– Often contains small stones (gravel) that the bird has swallowed which
aid in the grinding process
– Function similar to that of teeth and jaws
– Food then passes through the pyloric sphincter to the small intestine
– Small Intestine:
• Bile and enzymes manufactured in the liver, pancreas, and intestine further
break down the food
• Digested food absorbed into the blood
Bird Digestive System
• Birds have a number
of adaptations that
enable them to fly,
including an efficient
digestive system
• Trace the path of food
through the digestive
system
Bird Digestive System
Bird Digestive System
• In some birds, such as pigeons, the
crop has a second function
• During nesting season, the breakdown of
cells in the crop produces a substance that
is rich in protein and fat
• Parent birds regurgitate this substance
and feed their newly hatched young with it
• This substance provides the young birds
with materials they need to grow
BIRD DIGESTIVE SYSTEM
BIRD DIGESTIVE SYSTEM
Bird Digestive System
• From the crop, moistened food moves into the stomach
• The form that a bird's stomach takes depends on the
bird's feeding habits
• Birds that eat meat or fish have an expandable area in
which large amounts of soft food can be stored
• Birds that eat insects or seeds, however, have a
muscular organ called the gizzard that helps in the
mechanical breakdown of food by grinding it
– The gizzard forms part of the stomach
– In many species of bird, the gizzard contains small pieces of
stone and gravel that the bird has swallowed
• The thick, muscular walls of the gizzard grind the gravel and food
together, crushing food particles and making them easier to digest
Bird Digestive System
• Food moves from the stomach to the small
intestine, where the breakdown of food is
completed and food is absorbed into the
body
• Digestive wastes leave the body through
the cloaca
• The activity at right tests your knowledge
of the parts of a bird's digestive system
Respiration
• Birds have a unique and highly efficient way
of taking in oxygen and eliminating carbon
dioxide
• When a bird inhales, most air first enters
large posterior air sacs in the body cavity
and bones
– The inhaled air then flows through the lungs
– Air travels through the lungs in a series of small
tubes
– These tubes are lined with specialized tissue,
where gas exchange takes place
Bird Respiratory System
• Birds have a unique
respiratory system
• Air sacs direct air
through the lungs in
an efficient, one-way
flow
Bird Respiratory System
Bird Respiratory System
• The complex system of air sacs and
breathing tubes ensures that air flows into
the air sacs and out through the lungs in a
single direction
– The one-way flow constantly exposes the lungs to
oxygen-rich air
• Contrast this to the system found in most
land vertebrates, in which oxygen-rich air is
inhaled, and oxygen-poor air is exhaled
– The air travels in two directions, in and out. In an
in-out system, the lungs are exposed to oxygenrich air only during inhalation
BIRDS
INTERNAL ANATOMY
•
Respiratory System:
– High metabolic rate requires large amount of oxygen
– Elaborate and highly efficient system
• Even at higher altitudes where oxygen levels are low
– Air enters the paired nostrils
• Passes down the trachea past the syrinx (song box) and enters the two
bronchii
• From the bronchii, air moves to the lungs
• 75% of the air bypasses the lings and flows directly to posterior air sacs
– 9 air sacs extend out from the lungs
» Connect with air spaces in the bones, filling hallow bones with air
» Function in respiration but also greatly reduce the bird’s density
• Exhalation:
– When a bird exhales carbon dioxide-rich air from the lungs, oxygen-rich
air is forced out of the posterior air sacs into the lungs via small tubes
– Thus, lungs receive oxygen rich air during Inhalation and Exhalation
Bird Respiratory System
• What advantage does the efficient
respiratory system of birds provide?
• The constant, one-way flow of oxygen-rich
air helps birds maintain their high metabolic
rate
• Birds need a high metabolism to maintain
body temperature and provide the large
amounts of energy required for flight
• In addition, the efficient extraction of oxygen
enables birds to fly at high altitudes where
the air is thin
BIRD RESPIRATORY SYSTEM
BIRD RESPIRATORY SYSTEM
Circulation
• Birds have four-chambered hearts and two separate
circulatory loops
– Unlike that of amphibians and most reptiles, birds have two
separate ventricles, the right ventricle and the left ventricle
– There is complete separation of oxygen-rich and oxygenpoor blood
– One half of the heart receives oxygen-poor blood from the body
and pumps this blood to the lungs
– Oxygen-rich blood returns to the other side of the heart to be
pumped to the rest of the body
• This double-loop system ensures that oxygen
collected by the lungs is distributed to the body
tissue with maximum efficiency
Bird Heart
• To keep blood moving
rapidly, a bird’s heart
beats quickly—from
150 to more than
1000 beats per
minute!
• Why is it important for
a bird’s heart to move
blood so rapidly?
Bird Heart
BIRDS
INTERNAL ANATOMY
• Circulatory System:
– Four chambered heart
• Right side receives deoxygenated blood from the
body and pumps it to the lungs
• Left side receives oxygenated blood from the lungs
and pumps it to the body
– Single right aortic arch (unlike amphibians
and reptiles)
– Rapid heartbeat
• Chickadee (1,000/minute); hummingbird
(600/minute); ostrich (70/minute)
BIRD CIRCULATORY SYSTEM
Excretion
• The excretory systems of many birds are
similar to those of most living reptiles
• Nitrogenous wastes are removed from
the blood by the kidneys, converted to
uric acid, and deposited in the cloaca
• There, most of the water is reabsorbed,
leaving uric acid crystals in a white,
pasty form that you may recognize as
bird droppings
Response
• Birds have well-developed sense organs, which are adaptations that
enable them to coordinate the movements required for flight
• Birds also have a brain that can quickly interpret and respond to a
lot of incoming signals
• A bird's brain is relatively large for its body size
• The cerebrum, which controls such behaviors as flying, nest
building, care of young, courtship, and mating, is quite large
• The cerebellum is also well developed, as you might expect in an
animal that uses precise, coordinated movements
• The medulla oblongata coordinates basic body processes, such as
the heartbeat
BIRDS
INTERNAL ANATOMY
• Nervous System
–
–
–
–
–
Large brain in relation to their size
Cerebrum controls navigation
Most have
good color vision
Eyes:
• Most birds: on the side of the head (giving a wide field of vision)
• Some birds: located near the front of the head have better binocular
vision (better depth perception)
– Ears:
• No external ears
• Feathers around the ear opening direct sound
– Smell: less developed except ducks and flightless birds
• Note: small Olfactory Lobes in diagram
– Taste: helps avoid bitter tasting or toxic foods
Bird Brain
• Compared to reptiles,
birds have an
enlarged cerebellum
that coordinates the
movements of wings
and legs.
Bird Brain
BIRD BRAIN
Response
• Birds have extraordinarily well developed eyes
and sizable optic lobes in the brain
• Birds see color very well—in many cases,
better than humans
• Most bird species can also hear quite well
• The senses of taste and smell, however, are
not well developed in most birds, and the
olfactory bulbs in a bird's brain are small
EYES/EARS
Movement
• Some birds cannot fly
• Instead, they get around mainly by walking
or running, like ostriches, or by swimming,
like penguins
• However, the vast majority of birds can fly
• The skeletal and muscular systems of
flying birds exhibit adaptations that enable
flight
WINGS
Movement
•
•
•
•
•
•
•
•
Observe a bird's skeletal system in the
figure at right
Although the bones in a bird's wings are
homologous to the bones in the front limbs
of other vertebrates, they have very different
shapes and structures
In flying birds, many large bones, such as
the collarbone, are fused together, making a
bird's skeleton more rigid than a reptile's
These bones form a sturdy frame that
anchors the muscles used for flight
The bones are strengthened by internal
struts similar to those used in the framework
of tall buildings and bridges
Air spaces make many bones lightweight
Birds also have large chest muscles that
power the upward and downward wing
strokes necessary for flight
The muscles attach to a long keel that runs
down the front of an enlarged breastbone, or
sternum
Bird Skeleton
•
•
•
•
Like most of its anatomy, a bird’s
skeleton is well adapted for flight,
providing a sturdy attachment
point for muscles
The long bones are
exceptionally strong and light
because of cross-bracing and
air spaces
In strong flying birds, such as
pigeons, the chest muscles may
account for as much as 30 percent
of the animal’s mass
If this pigeon has a mass of 200
grams, and 30 percent of its mass
is chest muscles, what is the mass
of its chest muscles?
Bird Skeleton
BIRDS
INTERNAL ANATOMY
•
Skeleton and Muscles
– Natural selection has favored a lightweight body, yet the powerful muscles give it
unusual strength
– Axial skeleton combines lightness and strength
• Bones are thin and hallow with cross struts
• Many bones fused making the skeleton more rigid
– Provides for stability in flight
– Sturdy framework for anchoring the powerful breast muscle during flight and supporting the leg
muscles when walking or at rest
– Furculum (wishbone) (fused collarbones)
– Sternum: keeled
• Supports the breast muscles
• Humerus, ulna, radius, pectoral girdle ,and the sternum support the wing
– Pygostyle: terminal verteba of the spine
• Supports the tail feathers which play an important role in flight providing additional lift
and aiding in steering and braking
– Flight:
• Air flows above and below the wing, creating lift (Bernoulli’s principle)
• Muscles in the skin move the feathers permitting precise flight maneuvers
BIRD SKELETON
BIRD SKELETON
MIGRATION PATTERNS
Reproduction
• In birds, both male and female reproductive
tracts open into the cloaca
– The sex organs often shrink in size when the
birds are not breeding
• As birds prepare to mate, the ovaries and
testes grow larger until they reach
functioning size
• Mating birds press their cloacas together to
transfer sperm from the male to the female
• Some male birds have a penis that transfers
sperm to the female's cloaca
Reproduction
• Bird eggs are amniotic eggs
– They are similar to the eggs of reptiles but have
hard outer shells
• Most birds incubate their eggs until the eggs hatch
• When a chick is ready to hatch, it uses a small tooth on
its bill to make a hole in the shell
• After much pushing, poking, and prodding by the chick,
the eggshell breaks open
• Once the exhausted bird has hatched, it collapses for a
while and allows its feathers to dry
• Both parents may be kept busy providing food for their
hungry offspring
BIRDS
INTERNAL ANATOMY
•
Reproductive System:
– Separate sexes
– Fertilization: internal
– Male:
• Two testes lie beneath the kidneys
• Sperm pass through small tubes called vasa deferentia into the cloca
– Mating:
• Male presses his cloaca to the female’s and releases sperm
– Female:
• Most have a single ovary on the left side
– Releases eggs into a long, funnel-shaped oviduct where fertilization takes place
– Fertilized eggs move down the oviduct, where they receive protective covering and a calcium
carbonate shell secreted from a shell gland
– Egg:
• Unfertilized consist of a nucleus, cytoplasm, and a yolk
• Fertilized:
– Embryo suspended in albumen (egg white)
– Chalaza:
» ropelike strand that support the liquid medium
» Attached to the shell membrane
BIRD MALE REPRODUCTIVE SYSTEM
BIRD FEMALE REPRODUCTIVE SYSTEM
BIRDS
INCUBATION
• Female birds usually lay eggs in nest
• Incubation:
– Either parent may sit on the eggs covering
them with a thickened, featherless patch of
skin on the abdomen called a brood patch
– Other varieties of brooding exist
BIRDS
DEVELOPMENT
• Embryo development begins when the zygote forms a plate of cells
on the surface of the yolk
– Plate forms the tissues and organs of the embryo
• Yolk sac membrane grows out of the embryo’s developing digestive
tract and surrounds the yolk like a net
– Produces digestive enzymes that dissolve proteins and lipids in the yolk
– Blood vessels in the membrane carry nutrients to the embryo
• Allantois: vascular, netlike sac
– Grows from the digestive tract
– Attaches to the chorion membrane lining the shell
– Allantois and chorion function in respiration and excretion
• Amnion: encases the embryo
• Egg tooth:
– Helps break crack the shell
– Falls off after hatching
BIRD EGG
Groups of Birds
• Birds fill the woods and fields with song. Imagine
how dull the world would be without the color,
song, and variety of birds
• With nearly 30 different orders, it is impossible
to present each type of bird here
• By far, the largest order of birds is the
passerines, or perching birds
– This group includes songbirds such as larks,
sparrows, and finches
– There are over 5000 species of perching birds
BIRD EGG
EMBRYONIC DEVELOPMENT
EMBRYONIC DEVELOPMENT
BIRDS
REARING YOUNG
• Two Methods: different degrees of parental care
– Precocial Young:
•
•
•
•
•
Lay many eggs
Incubate for long period
Young active at hatching
Quite advanced in their development
Young relatively independent
– Can feed themselves, walk, and swim
– Altricial Young:
• Lay a few eggs
• Hatch quickly
• Young blind, naked, and helpless
– Completely dependent on parents
• Depend on parents for weeks
BIRD NEST
HUMMINGBIRD: MUD
BIRD NEST
OSPREY: BRANCHES
BIRD NEST
WEAVER: GRASS
BIRD NEST
TREE
BIRD NEST
KINGFISHER: RIVERBANK
BIRD NEST
ALTRICIAL YOUNG
BIRD NEST
PRECOCIAL YOUNG
Diversity in Birds
• Birds show
remarkable diversity
and inhabit many
different
environments
• Some representative
groups are shown
• Which group of birds
is the largest?
Diversity in Birds
Ecology of Birds
• Because birds are so numerous and diverse, they
interact with natural ecosystems and human society
in many different ways
• For example, hummingbirds pollinate flowers in both
tropical and temperate zones
• Fruit-eating birds swallow seeds but may not digest
them, so their droppings disperse seeds over great
distances
• Insect-eating birds, such as swallows and chimney
swifts, catch great numbers of mosquitoes and other
insects, and therefore help control insect
populations
Ecology of Birds
• Many birds migrate long distances—often over
hundreds of kilometers of open sea
• Such migrations are usually seasonal
• It can be startling during a winter visit to a tropical
country to see Northern orioles or bright red cardinals
flitting around banana trees with parrots and toucans
• How do migrating birds find their way?
• Some species use stars and other celestial bodies
as guides
• Other species may use a combination of landmarks
and cues from Earth's magnetic field
MIGRATION PATTERNS
Ecology of Birds
• Because birds are highly visible and are an important part of
the biosphere, they can serve as indicators of environmental
health
• It is no accident that conservationist Rachel Carson chose
songbirds for the focus of her pioneering campaign in the
1960s against the careless use of DDT and other pesticides
• In her book Silent Spring, Carson described to the public for the
first time how pesticides that stay in the environment can
accumulate in food chains and cause harm to animals they were
never intended to affect
• Thanks to the efforts of Carson and other conservationists, many
birds—especially predators such as eagles and ospreys—have
returned from the brink of extinction