Transcript Reptiles and Birds

Reptiles and Birds
Characteristics of Reptiles
• Members of the class Reptilia live
throughout the world in a wide variety of
habitats, except in the coldest regions, where
it is impossible for ectotherms to survive.
• Reptiles share certain characteristics, features
they retain
from the time when
reptiles replaced
amphibians as
the dominant
terrestrial vertebrates.
Characteristics of Reptiles
• Reptiles have a strong, bony skeleton,
and most have two pairs of limbs.
– Snakes and some lizards are legless.
• The legs of reptiles are positioned more directly
under their body than are the limbs of
amphibians.
• Reptiles have toes with
claws, which are used
for climbing and digging.
– Claws also enable reptiles
to get a good grip on the
ground, allowing many
reptiles to run quickly for short distances.
Characteristics of Reptiles
• The nervous system of a reptile is very similar
to that of an amphibian.
• Like their dinosaur
ancestors, modern
reptiles have a brain
that is small in relation to their body.
– An alligator about 2.5 m (8 ft) long has a brain
that is about the size of a walnut.
• Despite this small brain size, reptiles are
capable of complex behaviors, including
elaborate courtship.
Ectothermic Metabolism
• Reptiles’ ectothermic metabolism is too slow to
generate enough heat to warm their bodies, so they
must absorb heat from their surroundings.
• As a result, a reptile’s body temperature is largely
determined by the temperature of its environment.
• Many reptiles
regulate their
temperatures
behaviorally, by
basking in the
sun to warm up
or seeking shade
to cool down.
Ectothermic Metabolism
• At very low temperatures, most reptiles
become sluggish and unable to function.
• Intolerance of cold generally limits their
geographical range and, in temperate
climates, forces them to remain inactive
through the winter.
Water Retention
• Amphibians such as frogs cannot be
considered fully terrestrial because they lose
too much water through their skin.
• Amphibians must stay moist to avoid
dehydration, and
their method of
reproduction requires
a moist environment.
• Reptiles have evolutionary
adaptations that free them
from the water requirements of amphibians.
Watertight Skin
• Terrestrial animals face a serious
problem of water loss as water
evaporates through their skin.
• Modern reptiles have evolved
a skin made of light, flexible scales.
• These scales overlap
and form a protective,
almost watertight
skin that minimizes
water loss.
Watertight Eggs
• For a reptile living on dry land, reproduction
presents another serious water-loss problem.
• Without a watery environment, both sperm
and eggs will dry out.
• A reptile’s fertilized eggs need a moist
environment in which to develop.
• A reptile’s amniotic egg solves
the problem of a reptile
needing a moist environment
in which to develop.
Watertight Eggs
• An amniotic egg contains both a water
supply and a food supply and is key to a
reptile’s success as a terrestrial animal.
• Because the egg’s tough shell makes it
essentially watertight, it does not dry out,
even in very dry habitats.
• Most reptiles, all birds, and three species of
mammals reproduce by means of amniotic
eggs with shells.
• The formation of amniotic eggs with shells
suggest that these three groups of animals
evolved from a common ancestor.
The Amniotic Egg
• Both reptiles and birds have amniotic eggs,
which are very much alike internally.
• Although a reptile’s eggshell is leathery and a
bird’s is hard, both are almost watertight.
• However, the shells are porous enough to
allow oxygen to enter the egg and carbon
dioxide to leave.
• The shell and the albumen (egg white) protect
and cushion the developing embryo.
• The albumen is also a source of
protein and water for the embryo.
The Amniotic Egg
• Within the egg, four specialized membranes
(the amnion, yolk sac, allantois, and chorion)
play important roles in maintaining a stable
environment in which the embryo can develop.
• The amnion encloses the embryo within
a watery environment.
• This membrane creates
a little ‘pond’ that
substitutes for the water
in which amphibians
lay their eggs.
• This watery enclosure
protects the embryo by cushioning it.
The Amniotic Egg
• The yolk sac contains the yolk, the developing
embryo’s food supply.
• The embryo absorbs nourishment from the yolk
through blood vessels connecting its gut and the
yolk sac.
• The allantois is a sac that stores waste products
from the embryo.
• It also serves as the
embryo’s organ for
gas exchange.
• Blood vessels in the
walls carry oxygen
and carbon dioxide
from the embryo.
The Amniotic Egg
• Surrounding the amnion, yolk sac, and
allantois is a membrane called the chorion.
• The chorion allows oxygen to enter the egg
and carbon dioxide to leave.
Reptilian Lungs
• A reptile’s scaly skin does not permit gas
exchange, so reptiles cannot use their skin as an
additional respiratory surface.
• The lungs of most reptiles have many
respiratory folds.
• These folds greatly increase the respiratory
surface area of a reptile’s lungs.
• Reptiles also have strong muscles attached to
their rib cage.
• The action of these muscles
helps to move air into and
out of the lungs, increasing
the lungs’ efficiency.
Reptilian Heart
• In most reptiles, the septum which divides
the heart extends into the ventricle, partly
dividing it into right and left halves.
• The septum enables a much better, but still
incomplete separation of oxygen-rich and
oxygen-poor blood.
• As a result, oxygen is delivered
to the body cells more efficiently
than in amphibians.
Reptilian Heart
Reptilian Heart
• Unlike most reptiles, crocodilians have a
heart with a completely divided ventricle
that consists of two pumping chambers.
• This arrangement fully separates the lung
circulation from the body circulation.
• The delivery of oxygen
throughout the
crocodilian body
is further improved
in these animals.
Reptilian Reproduction
• Unlike the eggs of most amphibians, reptilian
eggs are fertilized within the female, during a
process called internal fertilization.
• The male reptile introduces his semen and
fluid sections.
• Internal fertilization protects the gametes
from drying out, even though the adult
animals are fully terrestrial.
Reptilian Reproduction
• Many reptiles are oviparous, meaning the
young hatch from eggs.
• In most cases, the eggs are not protected by
the parents.
• Most snakes and lizards, all turtles and
tortoises, and all
crocodilians are
oviparous.
• All birds and three
species of mammals
are also oviparous.
Reptilian Reproduction
• Some species of snakes and lizards are
ovoviviparous, which means the female
retains the eggs within her body until shortly
before hatching or the eggs may hatch within
the female’s body.
• Although the embryos receive water and
oxygen from the female, their nourishment
comes from the yolk sac.
• In ovoviviparous reptiles, the eggs are less
vulnerable to predators.
Modern Reptiles
Lizards and Snakes
• Snakes and lizards belong to the order
Squamata.
• A distinguishing characteristic of this order is a
lower jaw that is only loosely
connected to the skull.
• This allows the mouth to open
wide enough to accommodate
large prey and explains how an
anaconda (the world’s largest
snake) can swallow a jaguar.
• This ability is a contributing
factor to the success of snakes
and most lizards as predators.
Lizards
• Common lizards include iguanas,
chameleons, geckos, anoles, and horned
lizards (often mistakenly called “horny toads”).
• A few species of lizards are herbivores,
but most are carnivores.
• Most lizards are small, measuring less than 30 cm (1 fl) in
length, but lizards that belong to the
monitor family can be quite large.
• The komodo dragon of Indonesia
is the largest monitor lizard.
– It can be up to 3 m (10 ft) in length
and weigh up to 125 kg (275 lbs).
• The tail of some species of lizards, such as the gecko breaks
off easily when seized by a predator,
allowing the lizard to escape.
– Lizards can regenerate a new tail,
but it does not have any vertebrae in it.
Snakes
• Snakes probably evolved
from lizards during the Cretaceous period.
• The close relationship between lizards and
snakes is reflected in their many similarities.
– It is often difficult to distinguish the legless
species of lizards from snakes.
• Snakes lack movable eyelids and external
ears, as do several species of lizards.
• Both snakes and lizards
molt periodically, shedding
their outer layers of skin.
Snake Body Structure
• The skeleton of snakes is unique.
• Most snakes have no trace of a pectoral girdle
(the supporting bones for the bones of the
forelimbs), which is found even in legless lizards.
• The snake’s jaw is very flexible because it has
five points of movement.
– Human jaws have only one movement point.
• One of these points is the chin,
where the halves of the lower jaw
are connected by an elastic ligament.
• This ligament permits the
lower jaw to spread apart
when a large meal is
being swallowed.
Snake Feeding
• While many snakes simply seize their prey and swallow
it whole, some snakes use other methods to subdue their
prey.
• Many very large snakes (such as Anacondas, Boas, and
Pythons) are constrictors as are some smaller species
(such as King Snakes).
• Constrictors wrap their
body around their prey,
gradually squeezing
tighter and tighter until
the prey suffocates.
• The snakes then swallow
their prey whole, even if the prey is very large.
• Like all snakes, constrictors have no teeth that are suited
for cutting and chewing.
Snake Feeding
• Some snakes kill their prey
with venom (poison).
• Of the 13 or more commonly
recognized families of snakes,
only four are venomous.
– Cobras, Kraits, and Coral snakes
– Sea snakes
– Adders and Vipers
– Rattlesnakes, Water Moccasins,
and Copperheads
Snake Feeding
• In most venomous snakes, modified salivary
glands produce venom
that is injected into the
victim through grooved
or hollow teeth.
• The African Boomslang
and Twig Snakes produce
venom but do not inject it.
– Instead they bite their prey with fangs located
at the back of their mouth.
– Grooved teeth direct the venom into their
victim’s wound.
Rattlesnake
• Rattle – The rattle typically consists of
5 to 7 interlocking rings made of keratin,
a protein. When shaken, it produces a
rattling sound that serves as a warning.
Each time the snake sheds its skin during
molting, a new ring is added to the base of
the rattle. The more rapidly the snake grows, the more rattles it
accumulates during a given time.
• Pit Organ – Between each eye and nostril of the rattlesnake is an
organ that can detect infrared radiation. The snake can locate a
warm-bodied animal in a cool, nighttime environment by detecting
the difference in infrared radiation emitted by the animal and the
cooler background. This gives the rattlesnake the ability to hunt in
total darkness.
• Jacobson’s Organs – Flicking the forked tongue into the air, the
rattlesnake takes in chemical samples from the environment. These
chemicals are transferred to two depressions in the roof of the mouth
called Jacobson’s organs, which detect the odor of the chemicals. The
snake uses these organs to follow the scent trail of prey.
Rattlesnake
• Reproductive Structures – This male rattlesnake
produces sperm in his testes. Females are ovoviviparous.
After the eggs hatch in the mother’s body, the live young
are ejected and must fend for themselves.
Turtles and Tortoises
• There are about 250 or more species of
turtles (which generally live in water) and
tortoises (which live on land), all classified in
the order Chelonia.
• Turtles and tortoises differ from other
reptiles in that their bodies are
encased within a hard,
bony, protective shell.
• Many of them can pull their
head and legs into the shell
for protection from predators.
Turtles and Tortoises
• While most tortoises have a dome-shaped
shell, water dwelling turtles
have a streamlined, diskshaped shell that permits
rapid maneuvering in water.
• Turtles and tortoises lack teeth
but have jaws covered by sharp
plates, which form powerful beaks.
• Many are herbivores but
some, such as the snapping
turtle, are aggressive carnivores.
Turtles and Tortoises
• Modern turtles and tortoises differ
little from the earliest known
turtle fossils, which date to more
than 200 million years ago.
• This evolutionary stability may
reflect the adaptive aspect of their
basic shell-covered body structure.
Turtle Evolution
Turtles and Tortoises
• The shell is made of fused plates of bone covered
with horny shields or tough, leathery skin.
• In both cases, the shell consists of two basic parts.
• The carapace is the dorsal (top) part of the shell,
and the plastron is the ventral (bottom) portion.
• The vertebrae and ribs of most species are fused
to the inside of the carapace.
• The shell provides the
support for all muscle
attachments in the torso.
Crocodilia
• The order Crocodilia is composed of 25
species of large, aquatic reptiles.
• Of all the living reptiles, the crocodilians are
most closely related to the dinosaurs.
• In addition to the crocodiles and alligators,
the order Crocodilia includes the alligator-like
caimans and the long-snouted gavial.
Crocodiles and Alligators
• Crocodilians are aggressive carnivores.
• Some are quite large.
– American alligators can reach 5.5 m (18 ft) in length,
and Nile crocodiles can reach 6 m (20 ft) in length
and weigh 750 kg (1,650 lb).
• Crocodilians generally capture prey by stealth,
often floating just beneath the water’s surface
near the shore.
• When an animal comes to the water to drink, the
crocodilian explodes out of the water and seizes
its prey.
• The crocodilian then hauls
the prey back into the water
to be drowned and eaten.
Crocodiles and Alligators
• The bodies of crocodilians are well adapted for
this form of hunting.
• Their eyes are high on the sides of the head,
and their nostrils are on top of the snout.
• As a result, they can see and breathe while lying
nearly submerged in the water.
• Crocodilians have a strong
neck and an enormous mouth
studded with sharp teeth.
• A valve in the back of the
mouth prevents water from entering the lungs
when crocodilians feed underwater.
Crocodiles and Alligators
• Unlike other living reptiles, crocodilians care
for their young after hatching.
• A female American alligator builds a nest of
rotting vegetation for her eggs.
• After the eggs hatch, the mother may tear
open the nest to free the hatchlings.
• The young alligators remain
under her
protection for
up to a year.
Tuataras
• The order Rhynchocephalia contains only
two species of tuataras.
• The two living species of tuataras are members
of the genus Sphenodon and are native
to New Zealand.
• Tuataras are lizard-like reptiles up to 70 cm
(2 ft) long.
• Unlike most reptiles, tuataras are most active
at low temperatures.
Tuataras
• They burrow or bask in the sun during the day
and feed on insects, worms, and other small
animals at night.
• Tuataras are sometimes called living fossils
because they have survived almost
unchanged for 150 million years.
• Since the arrival of humans to New Zealand
about 1,000 years ago, the tuatara’s range has
diminished, and their members
are declining.
Characteristics of Birds
• The birds we see today are the modern members
of the class Aves.
• Unlike their reptilian relatives, birds usually lack
teeth and have a tail that is greatly reduced in
length.
• Birds lay amniotic eggs that are very similar to
those of reptiles, and the feet and legs of birds
are covered with scales.
• Other characteristics
unique to birds are the
presence of feathers
and the modification
of the forelimbs into wings.
Feathers
• Feathers are modified reptilian
scales that develop from tiny
pits, called follicles, in the skin.
• Just as snakes and lizards
replace their skin by molting,
birds molt and replace
their feathers.
• However, few birds shed all
of their feathers at one time.
Feathers
• Birds have two main types of feathers:
contour feathers and down feathers.
• Contour feathers cover the bird’s body
and give adult birds their shape.
• Specialized contour feathers,
called flight feathers, are found
on a bird’s wings and tail.
• These feathers help provide
lift for flight.
Feathers
• A contour feather has many
branches called barbs.
• Each barb has many
projections, called barbules
that are equipped with
microscopic hooks.
• These hooks link the
barbs to one another,
giving the feather a
continuous surface and
a sturdy flexible shape.
Feathers
• With use, the connections of the hooks and
barbs become undone.
• When you see a bird pulling its
feathers through its beak, it is
relinking these connections.
• This process is called preening.
• Most birds have a gland called
a preen gland which secretes oil.
• When a bird preens, it spreads the oil over its
feathers, cleaning and waterproofing them.
Feathers
• Down feathers cover the body of young
birds and are found beneath the contour
feathers of adults.
• Their soft, fluffy structure provides good
insulation for the bird, helping the bird
conserve body heat.
Feathers
• There are other reasons that
feathers are important to birds.
• Their coloration may be protective
(as camouflage) or may be
important in the selection of a mate.
– The feathers of some birds allow them to blend in
with their surroundings.
– In some species, the males
develop special plumage
during the breeding season.
Avian Skeleton
• The bones of birds are thin and hollow.
• Many of the bones are fused, making a bird’s
skeleton more rigid than a reptile’s.
• The fused sections form a sturdy frame that
anchors muscles
during flight.
Avian Skeleton and Muscles
• The power for flight (or for swimming underwater,
like penguins) comes from large breast muscles
that can make up to 30% of a birds body weight.
• These muscles stretch from the wings to the
breastbone.
• The breastbone is greatly enlarged and bears a
prominent keel for muscle attachment.
• Muscles also attach to the fused collarbones
(wishbone).
– No other living
vertebrates
have a keeled
breastbone
or fused
collarbones.
Endothermic Metabolism
• Birds are endotherms; they generate
enough heat through metabolism to
maintain a high body temperature.
• Birds maintain body temperatures ranging
from 40°C to 42°C (104°F to 108°F), which is
higher than the body temperature of most
mammals.
• These high temperatures are due to a high
rate of metabolism, which satisfies the
increased energy requirements of flight.
Avian Heart Structure
• The ventricle of birds is completely divided
by a septum.
• Oxygen-rich and oxygen-poor blood is kept
separate, meaning that oxygen is delivered
to the body cells more efficiently.
• The sinus venosus, which is a prominent part
of the fish heart, is not a separate chamber of
the heart in birds (or mammals).
– However, a small amount of tissue from it
remains in the wall of the right atrium.
– This tissue is the point of origin of the heartbeat
and is known as the heart’s pacemaker.
Avian Heart Structure
Avian Lungs
• Birds use a considerable amount of energy
when they fly.
• Since birds often fly for long periods of time,
their cellular demand for energy exceeds that of
even the most active mammals.
• To increase the efficiency of lungs, birds have
air pass over the respiratory surface
in one direction only.
• One-way air flow is possible
in birds because they have air
sacs connected to their lungs.
• There is no gas exchange in the
air sacs, they act as holding tanks.
Avian Lungs
• There are two important advantages to oneway air flow.
• First, the lungs are exposed only to air that is
almost fully oxygenated, increasing the
amount of oxygen transported to the body
cells.
• Second, the flow of blood in the lungs runs in
a different direction than the flow of air does.
• The difference in direction increases oxygen
absorption.
Avian Respiration
Avian Digestive System
• Large meals are temporarily stored in the crop,
the expandable lower portion of the esophagus.
• The food then passes into a
two-chamber stomach.
• In the first chamber, stomach acids begin
breaking down the food.
• The partially digested food
is then passed to the second
chamber, the gizzard, where
it is ground and crushed.
• Undigested material
is eliminated
through the cloaca.
Avian Excretory System
• The excretory system is efficient and
lightweight.
• It does not store waste liquids in a bladder.
• Instead, birds convert nitrogenous
waste to uric acid, which is concentrated
into a harmless
white paste.
• The uric acid travels
to the cloaca and
is eliminated.
External Avian Structures
Adaptations of Birds
• There is great diversity among
the 28 orders of birds.
• 60% of all birds species belong
to order Passeriforms.
– These birds, also known as the songbirds,
number approximately 5,300 species and are by
far the largest group of terrestrial vertebrates.
• Birds are adapted for different ways of life.
• You can tell a great deal about the habitats
and diets of birds by examining its beak
(bill), legs, and feet.
Adaptations of Birds
• During the evolutionary history of birds,
their beaks, legs and feet have been
adapted to the particular environment
the birds live in.
• Some birds are
more highly
specialized than
others, and many
birds are highly
flexible in their eating habits.
Adaptations of Birds
Type of Bird
Beak adaptations
Songbirds (cardinal, robin) Seed-cracking: short,
thick strong beak
Foot Adaptations
Perching: Toes can cling
to branches; one toe points
backward
Insect-catching: Long,
slender beak for probing
Hummingbirds
Probing: Thin, slightly Hovering: Legs so small
curved beak for inserting the bird cannot walk on the
into flowers to sip nectar ground;
tiny feet
Woodpeckers
Drilling: Strong, chisel- Grasping: Feet with two
like beak
toes pointing forward
and two
pointing
backward
Adaptations of Birds
Type of Bird
Beak adaptations
Foot Adaptations
Parrots
Cracking, Tearing: Short,
stout, hooked beak used to crack
seeds and
nuts and
to tear
vegetation
Climbing/Grasping:
Strong toes two pointing
forward, two pointing
backward,
adapted for
perching,
climbing,
and holding
food
Birds of Prey
Tearing: Curved, pointed beak
for pulling apart prey
Grasping: Powerful,
curved talons for seizing
and
gripping
prey
Adaptations of Birds
Type of Bird
Beak adaptations
Foot Adaptations
Ducks
Sieving: Long, flattened,
rounded bill
Swimming: Three toes
linked by webs for
improved swimming
Long-legged Waders
Fishing: Long, slender,
spear-shaped beak for
fishing
Wading: Long legs, toes
spread out over a large
area to support bird on
soft surfaces
Other Bird Adaptations
• There are many groups of
birds, each of which is
adapted to its particular
living conditions.
– Gulls and Terns have
streamlined bodies that are
adapted for flying over
the water in search of fish.
– Owls’ excellent low-light
vision enables them to
survive as nocturnal
hunters.