wildlife fact file - animal behavior - pgs. 81-90
DESCRIPTION
Evolution of Mammals, Evolution of Fish, The Falcon Family, How Animals Stay Clean, Lizards, Flightless Birds, Frogs and Toads, How Mammals Swim, How Mammals Hunt, MarsupialsTRANSCRIPT
"" CARD 81 EVOLUTION OF MAMMALS
Mammals were once on insignificant group of vertebrates. But after the decline and extinction of dinosaurs about 6S million years ago,
mammals came to dominate the animal kingdom in some ways.
KEY FACTS
THE RISE OF MAMMALS
Scientists disagree about what
brought an end to the Age of
Dinosaurs some 65 million years
ago. But whatever the cause, di
nosaurs had totally disappeared
within a million years. Mammals
then expanded rapidly in forms
and sizes, filling vacant spots in
the planet'S ecology.
About 80 million years before
the dinosaurs disappeared, the
mammals split into two main
reproductive groupings: marsu
pials and placental mammals. A
marsupial gives birth after a very
short gestation period, when its
offspring is barely formed. The
infant then spends a number of
months feeding on its mother's
milk, usually within her pouch.
A placental mammal has a more
efficient initial method of devel-
WHAT IS A MAMMAL?
All mammals feed their young
with milk that is produced by
the mother's body. No other
class of animals does this.
Several mammalian features
are found in other vertebrates.
Most mammals give birth to live
young, but so do some fish and
amphibians. On the other hand,
monotreme mammals (the platy
pus and echidnas) lay eggs.
opment for its young in which
the offspring remains inside the
womb for a longer time than a
marsupial does. It is nourished
by the mother's blood via the
placenta, an organ attached to
the womb lining.
Right: Kangaroos and other marsupials spend a long time developing in their mothers' pouches.
Right: All but three species of mammal give birth to live offspring. But this characteristic appears in other classes of animals as well.
Most mammals are hairy and
warm-blooded with fairly steady
Left: A female mammal's production of milk for her offspring is called lactation. This process is unique to all mammal species.
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l eft: Young wandering shrews and all other placental mammals spend longer developing in the womb than young marsupials do. As a result, newborn placental mammals need less help than newborn marsupials.
body temperatures, but some,
including humans, are almost
hairless. Others may vary their
body heat, especially if they hi
bernate. While most mammals
are active, consuming lots of en
ergy, tree sloths are sluggish.
Mammals have a few unique
skeletal features, such as a lower
jaw that is formed from a single
bone on each side.
0160200901 PACKET 90
The earliest mammals were small, shrewlike creatures. ~ THE FIRST MAMMALS ~ EVOLUTION & EXTINCTION The tremendous diversity of modern mammal species
evolved from these ancient animals. Today mammals
range in size from the featherweight pygmy shrew
to the 130-ton blue whale. They have adapted to
all of the Earth's environments. One group of
mamma/~the bat~has even learned to fly.
~ FROM REPTILES TO MAMMALS Mammals evolved very gradually from reptiles. Approximately 300 million years ago, the first true reptiles, known as diapsids and synapsids, appeared. Diapsids were the ancestors of dinosaurs and today's birds, lizards, snakes, and crocodiles. Synapsids were the ancestors of various reptiles, including the ones that evolved into mammals.
legs. They also had flexible vertebrae, possibly enabling them to curl up. They may even have suckled their young.
Probably, later mammal-like reptiles had hair, more constant body temperatures, and sweat glands that were modified to give milk for the young. Like today's monotremes (egg-laying mammals), the first true mammals probably laid eggs.
By 225 million years ago, there were some mammal ancestors that seemed closer to mammals than reptiles. One example is the shrewlike Megazostrodon.
Yet for 150 million years, dinosaurs dominated the world. Fossils indicate that all the earliest true mammals were small. Only after the sudden decline of dinosaurs, approximately 65 million years ago, did mammals begin to develop the great variety of forms and sizes that we know today.
During the years of dinosaur supremacy, mammals consolidated their efficient basic design. They evolved a powerful four-chambered heart as well as a diaphragm to help them inhale and exhale and to supply the lungs with oxygen. A "false" palate in the roof of the
By the middle Triassic period, 230 million years ago, some reptiles had become mammallike. The reptile's multi boned lower jaw began changing into the mammal's single-boned jaw. In addition, unspecialized reptilian teeth began to evolve into specialized mammalian teeth with incisors in front, followed by large canines, premolars, and molars.
Megazostrodon
A group known as cynodonts were equipped with fairly large, doglike skulls and mammal-like legs rather than squat reptilian
Thrinaxodon
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Haramiya
Kuehneotherium
MID-TRIASSIC PERIOD 225 million years ago
mouth enabled them to eat and breathe at the same time. Haircovered skin containing sweat glands helped the animals remain warm or cool according to need. Perhaps most significant, the skull became larger to hold an increasingly large and capable brain.
Front cover: Big cats such as the mountain lion are usually the top predators in their range.
Front insets: Mammals such as the greater horseshoe bat (left) and the killer whale (right) have evolved to conquer the skies and oceans.
Below: Thrinaxodon was a small, swift flesh eater that could regulate its own body heat. Its descendants split into three main groups. Two of these survived and evolved into today's mammals, from the duckbilled platypus to chimpanzees and humans.
There were three main groups of early mammals. They can be distinguished from one another by their teeth. Megazostrodon
was the ancestor of the insecteating mammals. Its cheek teeth -premolars and molars--€ach had three cusps (raised points) arranged in a line, helping the animal slice the hard shells and wing cases of its insect prey. Today, the only surviving descendants of Megazostrodon are the egg-laying mammals.
Living about 230 million years ago, Haramiya was the ancestor of rodents. It had large, gnawing incisors and cheek teeth that had several cusps to grind plant matter. This line of early mammals became extinct about 60 million years ago because it was not able to compete successfully with the descendants of the
Taeniolabis
EARLY CRETACEOUS PERIOD 140 million yeors ogo
third and most adaptable early mammal-Kuehneotherium.
Kuehneotherium had cusps on its premolars and molars that enabled it to crush and slice. Its descendants-the pantotheres -adapted to a wide variety of diets and became the ancestors of all of today's mammal species except the monotremes.
Fossilized skeletons of an early pantothere called Crusafontia indicate that it was a small, treedwelling insect eater. Its body length was approximately eight inches. It had a long tail, which probably helped it to balance and may also have been prehen
sile (capable of gripping twigs and branches). This squirrel-like animal is believed to be the ancestor of whales, kangaroos, elephants, bats, and most other mammals, including humans.
Duck-billed platypus
Chimpanzee
LATE QUATERNARY PERIOD Present day
EVOLUTION OF FISH
~--~- - --~~---- - - - --- - - ~
Fish were the first vertebrates to appear on earth, nearly S 00 million years ago. Since that time they have evolved into one
of the most diverse and successful of all animal groups.
KEY FACTS
FISH DIVERSITY
Some fish have developed ex
traordinary adaptations. Many that live in the ocean depths are
illuminated by rows of fluores
cent lights. These lights protect
the fish by imitating light from
the surface and disguising their
silhouettes. However, few pro
tective measures are effective
against a shark. It can detect
tiny electric impulses flickering
through a victim's nervous sys
tem, so it can find prey even in
dimly lit water.
The variety of shapes and col-
ors of fish is amazing. Some,
like clownfish, advertise their
identities with bright colors.
Others are well camouflaged.
The upright seahorse swims
Left: The electric eel of the Amazon basin has organs in its tail that can discharge up to 550 volts of electricity-enabling it to stun prey such as another fish or a frog.
FROM FISH TO LAND CREATURES
The fins of most fish consist of
flexible rays that are connected
to bones inside their bodies. In
bony fish the rays may be visi
ble. In others they are covered
yvith thick skin. In some fish, like
the lungfish and the coelacanth,
each fin has an internal bone
structure like that of an arm.
The bones support fin rays.
Such "lobe-finned" fish were
common in the Devonian peri
od, 400 million years ago. Fossils
suggest that they crawled out
of the water on limblike fins and
became the first vertebrates on
land. Eventually, their descen
dants lost their fin rays and ac
quired lungs, developing into
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Left: The flashlight fish lives in the ocean's dimly lit depths. Using a chemical process, its light-emitting organs produce a glow that confuses predators.
unnoticed among underwater
plants, and the gray-mottled,
flat flounder blends into the
ocean floor.
Many fish display remarkable
powers of navigation. In order
to spawn, a salmon can find
its way from the ocean back to
the freshwater stream where it
was born. It may detect chemi
cal changes in the water.
Some fish, such as the mud
skipper, are able to absorb oxy
gen from both air and water.
This amphibious lifestyle en
ables them to exploit extra
food sources.
creatures resembling newts.
These gave rise to reptiles and
ultimately birds and mammals.
Left: The fivefoot-long coelacanth is the closest living relative, of the first land vertebrates. Discoveredin 1938, this "living fossil" is almost identical to fossils that are as old as 140 million years.
01602009 11 PACKET 91
Although all fish are superbly adapted water-dwelling
vertebrates, there are many differences among them.
In fact the word fish encompasses a huge variety of
animals. To a biologist, a lamprey, a shark, and a perch
are no more alike than a snake, an eagle, and a gorilla.
~ FISH EVOLUTION The most primitive fish today are the 32 species of hagfish: wormlike scavengers with no jawbone and no true backbone, ribs, or skull. In place of jaws, a hagfish has a rasping tongue. A flexible rod of gristle called the notochord acts as a backbone.
Similar in appearance to hagfish are the 40 parasitic lamprey species, which suck body fluids from living fish. Lampreys do not have jawbones, but they have rudimentary skeletons made of cartilage.
Although hagfish and lampreys are grouped together as "jaw less fish," they are very different and are placed in separate classes. According to fossil remains, the first fish, such as Arandapsis, were also jawless
but had broad bodies armored with bony plates, which probably kept them on the seabed.
Fish with proper skeletons and jaws appeared much later. They evolved along two distinct lines represented by the other two classes of modern fish: sharks and rays in one class and bony fish in the other.
Sharks and rays have skeletons of cartilage, but bony fish have skeletons of true bone. The two types split apart some 400 million years ago and have been evolving ever since, with varying success. Bony fish have diversified into more than 20,750 species, compared to about 710 species of sharks and rays. These two classes account for over half the vertebrate species on earth.
~ WHAT IS A FISH? Fish come in many shapes and sizes and vary greatly in their habits. However, they all rely on water to supply them with needed oxygen, which they absorb through gills. They also depend on water to maintain a steady body temperature.
Another feature that all fish have in common is that they are vertebrates. A vertebrate is an animal with a backbone, a structure that evolved for the first time among fish about 480 million years ago. All the other vertebrates-amphibians, reptiles, birds, and mammalstrace their ancestry to those primeval fish.
Other vertebrates gradually found ways of living on land. But fish, with very few exceptions, have stayed in the water.
Front cover: The diverse wo:rl:d:O;f~~II~~~~E~iiill~~~~ fish includes fast-moving killers such as the great white shark, camouflaged ambushers like the toad fish (inset left), and primitive sucking parasites like lampreys (inset right).
Arandapsis
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DEVONIAN PERIOD 400 million years ago
Hemicyclaspis
~ LIVING IN WATER The main difference between living in water and living in air is that water is much denser, requiring more energy to move through it. The bodies of many aquatic animals such as jellyfish have much the same density as water, so they float. They do not need skeletons or muscles since the water holds them up.
Fish are supported in a similar way, but they are heavier, so they tend to sink slowly. Sharks and other fast-moving fish overcome this by swimming with their winglike fins angled upward. The related rays spend their adult lives on the seabed. Many bony fish have swim bladders (gas-filled buoyancy chambers) that they are able to fill or
empty in order to rise or sink. The density of water has two
further consequences. First, a fast-moving fish must be streamlined to pass through water easily. The torpedo-shaped bodies of marlins and sharks are good examples: Second, because water is so dense, fish can generate a lot of thrust if their fins are connected to strong muscles, even though the fins themselves are relatively small compared with a bird's wings.
The fins' muscles need a firm foundation, which is the main function of the backbone. The vertebrate skeleton evolved to enhance the swimming ability of fish. It developed into a supporting frame only after their
HOLOCENE PERIOD Today
descendants emerged from the water to live on land.
Living in water, fish must deal with the problem of becoming waterlogged or sometimes dehydrated. Water continuously passes into the body of a freshwater fish by a process called osmosis. Since the fish's body fluids are more concentrated than the surrounding water, the water seeps in to dilute them. In order to avoid becoming fatally bloated, the fish must constantly pump out water. For a marine fish, the problem is reversed. Its body fluids are less concentrated than the salt water around it, so water seeps out of its body. It must constantly drink water and expel the salt.
Cartilaginous fish: Sharks,
chimaeras, skates, and rays. Their skeletons,
made of carWage, are
lightweight.
Bony fish: The last group to evolve, it includes more
than 20,750 living species.
These fish have skeletons made
of true bone.
Jawless fish: These include
the most primitive living fish
species: hagfish and lampreys. They lack jaws
and have a pli-able notochord as a backbone.
THE FALCON FAMILY
There are about 60 falcon species throughout the world, ranging from the tiny, sparrow-size falconets of Southeast Asia to the great white gyrfalcon of Arctic North America and Eurasia.
KEY FACTS
HUNTING CHARACTERISTICS
Falcons in the genus Falco usual
ly have pointed wings and are
impressive fliers. The largest
such as the gyrfalcon and the
peregrine, lanner, saker, lugger,
and prairie falcons-are strong
predators, killing birds in midair.
Hobbies have long wings and
are very fast fliers. They feed pri
marily on large insects such as
dragonflies but can also catch
swifts, swallows, and bats.
Eleonora's falcon of the Medi
terranean and the sooty falcon
of North Africa seize small mi-
FALCON CONSERVATION
People have both admired and
persecuted falcons for centuries.
Falconry-a sport using trained
birds to hunt wild game-be
gan in the Far East about 4,000
DID YOU KNOW? • The rarest falcon is the Mau
ritius kestrel. Only 10 or so are
left on the island of Mauritius.
• In species like the peregrine
falcon, Barbary falcon, or gyr-
grating birds. The red-headed
falcon of Africa and India and
the merlin of northern Eurasia
and North America are fast little
falcons that hunt small birds in
open country.
South America's forest falcons
have short, rounded wings and
long tails, giving maneuverabili
ty. They twist and turn through
trees in pursuit of prey, which
they seize with their long legs.
Right: When it hunts, a kestrel hovers and scans the ground below for small mammals.
years ago. In medieval societies,
each noble rank was allotted a
particular falcon species. These
"noble hawks" were highly val
ued, and any peasants caught
harming them or stealing their
eggs were severely punished.
But attitudes toward falcons
changed in the 17th century.
Landowners and gamekeepers
destroyed them as pests, along
with other birds of prey. In addi
tion, collectors killed and stuffed
birds. Falcon eggs were prized
for their scarcity and the chal
lenge of taking them from cliff
ledge nest sites.
left: In Great Britain, the lanner falcon was traditionally used only by squires.
falcon, the female weighs near
ly twice as much as the male.
• The gyrfalcon is the only day
active bird of prey that is able to
survive the Arctic winter.
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Since World War II, sympathy
for falcons has grown, and there
has also been a revival of falcon
ry. Falcons are now protected in
many countries, and conserva
tion projects are trying to save
rare species such as the Mauri
tius kestrel.
But threats to falcons remain .
Because they are predators at
the top of the food chain, fal
cons may suffer severely from
pesticide pollution. Toxins build
up in their bodies when they eat
poisoned prey. The decline of
the peregrine falcon during the
1950s and 1960s as a result of
DDT alerted conservationists to
the destructive effects pesticides
can have on wildlife.
• The crested caracara is Mex
ico's national bird. Nicknamed
the "Mexican eagle," it is big,
w ith broad wings and slow
wing beats.
0160200991 PA KE
Although the falcon family includes the carrion-eating ~ DIFFERENT TYPES OF FALCON caracaras, all the other falcon species feed on a wide variety
of live prey. 50me of the smaller birds capture insects, voles,
and even snakes. Other members of the falcon family catch
birds the size of ducks and owls. Big species, such as the
peregrine falcon and the magnificent gyrfalcon, at
The falcons (Fa/conidae) are the
second biggest family of day
active birds of prey, after eagles,
vultures, and hawks. They live in
diverse habitats on every conti
nent except Antarctica. Some,
such as kestrels and peregrines,
may nest in city centers, while
others live in remote areas. times prey on mammals that are as large as hares. There are four subgroups: the
laughing and forest falcons; the
falconets and pygmy falcons;
the caracaras; and the true fal
cons (genus Fa/co).
~ ORIGINS It is thought that falcons initially
evolved in South America. The
caracaras, forest falcons, and
laughing falcon that now live
in South America may be direct
descendants of the first falcons.
Over time changes in
global climate resulted
in fewer forest areas and
more grasslands as well
European kestrel: This very adaptable bird lives in a variety of habitats. It generally hunts by hovering for some time on fast-beating wings and then swooping to the ground to snatch its prey in its feet.
laughing falcon: Named for its shrill call , which sounds like hysterical laughter. This bird specializes in catching snakes. After scanning the ground from a tree , it drops like a stone onto its victim.
as other kinds of open habitats.
Falcons then developed special
adaptations that exploited the
new habitats. The first birds re
sembling today's typical falcons
were probably kestrel-like
predators that hunted a
variety of prey using
several different
techniques.
The true falcons are the larg
est subgroup, with 38 species.
These aggressive birds include
the peregrine falcon, the gyrfal
con, and the hobbies, merlins,
and kestrels. Most are solitary
and defend their own hunting
and breeding territories. Some
Crested caracara: Inhabits open country in addition to mountains and forests. It is not a powerful hunter, feeding on sick or wounded animals as well as fish , frogs , and any carrion it finds. In contrast to other falcons ' sharp, curved talons, it has flat , blunt claws that are adapted for walking and scratching in soil or vegetation for insects.
Merlin: One of the smallest typical fal
cons , it hunts by flying fast and low over its moorland habitat, following each turn
of its bird prey.
tropical species live in pairs, de
fending a territory and hunting
together. Others, such as the
lesser kestrel and the red-footed
falcon, live in groups.
The falconets and pygmy fal
cons inhabit the tropics of Africa,
India, and Southeast Asia. They
are the smallest day-active birds
of prey. The laughing and forest
falcons are a little-known group
of seven primitive species in Cen
tral and South American forests.
There are nine caracara spe
cies. These primitive falcons live
only in the Americas. In contrast
to other falcons, they are bulky,
broad-winged birds with long
legs. They are sluggish, spend
ing much of their time perching
or walking around, searching
for food.
~ BREEDING Typical falcons remain with the
same mate for many years. The
courtship displays may involve
spectacular aerobatics with the
birds chasing each other and the
male diving, swooping, and roil
ing over on his back. At times he
circles with prey in his talons and
then drops it to the female be
low, who turns on her back to
catch it. During the display, the
birds give shrill chattering, cack
ling, and wailing calls. Later, they
frequently perform bowing cer
emonies at the nest site.
Instead of building nests, most
falcons lay their eggs on a rock
ledge, often using the same site
year after year. Kestrels may use
ledges on buildings. Some spe
cies nest in tree holes, using oth
er birds' abandoned nest holes.
Gyrfalcon: The largest " and most powerful falcon , it inhabits cliffs and uplands. It chases its mammal and bird
prey relentlessly, flying low over the ground ,
often for long distances.
African pygmy falcon: A bold pred-ator for its size, it kills large in
sects and small birds. It has large ear openings that help
it pinpoint the source of even the faintest rus
tle of its prey.
Caracaras, however, do create
untidy, bulky structures of sticks
and twigs in trees or cacti, on
cliffs, or on the ground.
In most species, both parents
incubate the eggs, although the
female spends more time on the
nest. The male usually feeds the
female during the egg-laying as
well as incubation periods.
The newly hatched chicks are
covered with thick white down
and then grow a longer, denser
coat of grayish down after 10 to
12 days. Small species remain in
the nest for four to five weeks
and larger species, six to seven
weeks. After they fledge, the
young are dependent on their
parents another two to three
weeks in smaller falcons and up
to eight weeks in large species.
Front cover: Like most typical falcons, the saker is a powerful hunter and prefers open country.
Front insets: The crested caraeara (left) is a primitive falcon. The pere
grine falcon (right) has been used by falconers for centuries.
HOW ANIMALS STAY CLEAN
Like humans, animals also try to keep themselves clean. But unlike us, they do not restrict themselves to baths and
showers or even to washing with water.
KEY FACTS
SOCIAL GROOMING
Mutual grooming often plays
a vital role in primate societies
and is part of the daily routine.
Unable to reach the fur on its
back, an individual must often
PREENING
Feathers are complex structures
that need a lot of care. In order
to fly well, a bird must keep its
plumage in good condition.
Most birds have preen glands
that produce an oil, which they
spread over their feathers with
their bills. This gland is largest in
water birds like ducks, geese,
petrels, and pelicans. Ducks and
geese preen up to 17 times daily
so that water rolls off their feath
ers, leaving them light and dry.
rely on another to keep the area
free of dirt and parasites.
Primates of all sizes-from go
rillas to chimpanzees--engage
in mutual grooming. This activi-
Left: The barbary ape lives in a highly organized community. Parents and older, nonrelated group members help groom the young.
Some birds expose their preen
gland to the sun to stimulate
the release of the oil.
Grooming movements can
serve as social signals among
birds. Courting birds may en
gage in ritualized mutual preen
ing. By turning its head away to
preen its feathers, a bird may in
dicate submission to its partner.
Right: Birds spend much of their time preening and always preen after a bath.
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ty usually takes place among rel
atives, strengthening the bond
between a paired male and fe
male or between a mother and
her young . But grooming unre
lated group members also has
its rewards. Vervet monkeys, for
example, live in big groups with
much rivalry and bickering. Sci
entists have observed a female
vervet helping an unrelated fe
male who groomed her earlier.
Thus, keeping clean not only
contributes to personal well
being, but it is also the founda
tion of social alliances.
Left: The anhinga can submerge silently in water due to its waterpermeable plumage. To keep its feathers in good condition, it spreads its wings to dry after fishing for food.
0160200881 PACKET 88
An animal cannot survive if its body is not adequately
shielded from the elements. It therefore needs some kind of
protective covering such as fur, feathers, scales, or thick skin. /"
This covering must be maintained in prime condition at all
times-by preening, bathing, or other cleaning methods.
~ FU R, FEATHERS &: SCALES Fur keeps an animal warm, but a bird's volume without contrib-it must be kept "open" to be ef- uting much to its weight. They fective. Fur insulates by trapping also form a waterproof outer lay-warm air between its fibers. If it er, enabling a bird to take off is caked with dirt, the fur cannot without being dragged down trap air. by the weight of the water.
Feathers provide better insula- The risk of infection from par-tion. Penguins have a thick layer asites or wounds is a problem of insulating fat under their skin. for all animals. If fleas and ticks But their dense down and stiff are not removed regularly from feathers playa key role in keep- a mammal's coat, infected sores ing them warm by maintaining develop. Bats lick their wings ev-a layer of warm air between the ery day to heal tiny nicks. Even skin and the Antarctic cold. snakes, with seemingly spotless
The oily feathers of water birds scales, must rub against rocks to provide buoyancy by adding to get rid of mites.
Front cover: Like many birds that eat carrion (dead animal flesh), the king vulture has no neck plumage to get soiled.
Front inset left: The Cape buffalo takes mud baths to soothe its skin and protect it from parasites.
Front inset right: A cleaner fish is able to obtain food by grooming larger fish such as angelfish.
Many animals have cleaning equipment right on their bodies. A bird such as a heron, bittern, or tinamou has a patch of down that grows continually on its breast and belly. The tips of these feathers constantly disintegrate to form a fine, waterresistant powder. As the bird preens itself or fluffs its breast feathers, the powder spreads over its body, helping to remove excess oil and grease that would impede flight.
Some mammals also have built-in cleaning equipment. The slow loris combs its fur with its long lower incisors,
Left: A lion must lick a wound almost constantly to prevent it from becoming infected.
Left: Grounddwelling birds such as the jungle fowl like to take dust baths to remove any excess oil from their plumage.
while the aye-aye lemur uses a thin claw on its index finger to untangle its fur and pick off parasites. The echidna has a special long claw on the second toe of its hind foot with which it scrapes off parasites from between its long spines.
Some animals actually provide a cleaning service for other species. Small, colorful fish that are called cleaner wrasse nibble dead skin, fish lice, and fungus off the scales of larger fish. The oxpecker, a small bird, provides a similar service by picking ticks and fleas off large grazing mammals.
Right: Water birds such as herons preen often in order to keep their feathers waterproof.
~ BATHING Wallowing in mud can serve a cleansing purpose. A mud bath helps remove ticks from a hippo's body and soothes the irritated skin. The mud also dries on the animal to form a thin crust that keeps parasites from getting to the skin.
Elephants also take mud baths and spend a great deal of time caring for their inch-thick skin. If possible, an elephant bathes in water daily, using its trunk to spray water over its own back or a companion's. After bathing, it rolls in dust or sprays dust on its back with its trunk to cover its skin with a thin film that protects against parasites.
Many birds, from house sparrows to eagles, also take dust baths. Desert birds and game
Left: Using its trunk, an elephant can spray its entire body with mud and water.
birds vigorously fluff up their feathers to create dust clouds, which help remove excess oils that might mat their feathers.
Some birds "bathe" in smoke, fumigating parasites from their feathers by flying right through smoke rising from a chimney.
A crow or jay may clean itself by spreading its wings, ruffling its plumage, and then sitting on an ants' nest, so that the insects can crawl through its feathers. It is not clear how this activity aids cleanliness, but the formic acid that the ants excrete may repel parasites, relieve itching, or destroy feather mites. The pangolin, an African mammal that has armorlike scales, also engages in "anting." It raises its scales to allow the insects to crawl underneath, then flattens the scales to crush the ants, creating an abrasive effect.
With more than 3,000 species, lizards outnumber all other reptiles. Extremely varied in shape and size, they have successfully colonized almost every habitat on earth.
KEY FACTS ~------<~~ ----------------------------~--------------------~
LIZARD FEATURES
Scales: Lizard scales are made of keratin-the substance that forms human fingernails. New scales constantly grow beneath the old ones, which the reptile sheds in patches. Lizard scales take many forms. The Gila monster and beaded lizard found in the southwestern United States have hard, knobby scales that repel predators, sand, and heat. The thorny devil's spikes, the crests of some male iguanas, and the "horns" of some chameleons are all modified scales. Limbs: Most lizards have very muscular legs with clawed feet for digging, running, or climb-
LIZARD DEFENSES Lizards have many different de
fenses against predators. Best known is their ability to shed their tails when attacked.
Some lizards rely on a quick
• The giant mosasaur lizards of 100 million years ago developed nostrils on their heads and paddlelike limbs similar to those of whales.
• Marine iguanas often dive to depths of 65 feet to forage for seaweed. These lizards have
ing-whatever the habitat demands. However, burrowing lizards like the so-called slowworm of Europe and the glass lizard of the United States have no legs at all. They move like snakes in sand or soft soil. Teeth: The teeth of lizards vary
escape. Fast-moving sand lizards like the fringe-toed lizard dive into the sand and "swim" away under the surface. In contrast, the chuckwalla from the
Left: A lizard's cast-off tail wriggles, distracting the predator while the lizard escapes. It will grow another tail later.
special glands for ridding their bodies of salt.
• When threatened, a horned lizard can squirt a drop of blood out of its eye in order to startle an enemy.
• Some lizards possess a "third eye," called a parietal eye, near
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Left: A chameleon has muscular legs and a gripping tail, so it can hold onto branches tightly while stretching out acrobatically to reach an insect.
according to their diet. Insect eaters have sharp teeth for seizing and holding prey. Plant eaters, such as iguanas, have teeth with serrated edges for ripping vegetation. The caiman lizard, which eats shellfish, has blunt teeth for crunching hard shells.
Southwest's deserts relies on staying put. It wedges its body into a crevice and keeps gulping air until it swells up like a balloon, making itself impossible to dislodge.
The Australian frilled lizard frightens away enemies by extending its huge throat frill and opening its mouth wide. To deter attackers, the African armadillo lizard holds its tail in its mouth, turning itself into an unapproachable spiny ball.
the back of the head. Covered in translucent skin, it acts as a light meter to help control the reptile's sun-basking hours.
• Most small lizards live a few years at most. But one captive slowworm reached the age of 54 years.
0160200881 PACKET 88
Lizards are found all over the world, from equatorial
deserts to cold regions inside the Arctic Circle. These reptiles
range in size from tiny geckos to massive monitors, and
they display an amazing variety of survival adaptations.
Some species are capable of gliding through the air. Other
lizards are able to move underneath sand dunes. Still
others can even patter across water on their hind legs.
~ ORIGINS Lizards share a reptile ancestor
with dinosaurs and crocodiles.
By the time the dinosaurs began
roaming the earth, lizards were
already evolving along a sepa
rate path.
The oldest known true lizard
fossils are from the late Triassic
period, 150 to 200 million years
ago. But many scientists believe
that there were earlier true liz
ards, which have not yet been
discovered in fossilized form.
One extinct group of lizards,
Front cover: Although Australia's thorny devil looks intimidating, it preys only on tiny ants.
Front inset left: The frilled lizard scares off its enemies by spreading its neck frill to make itself look bigger.
Front inset right: The komodo dragon is the heaviest lizard. It is a very fierce, powerful flesh eater.
the mosasaurs, lived in the sea.
At over 20 feet long, they were
much larger than modern liz
ards. No lizards live entirely in
the sea today, but marine igua
nas in the Galapagos Islands do
dive off rocks to find seaweed.
By the Oligocene epoch, 26
to 38 million years ago, many
lizards almost identical to mod
ern forms had appeared.
Right: A chameleon is able to grip branches firmly because it has opposable digits on its feet.
~ BREEDING Most lizards lay eggs, which are
placed in a scraped-out hollow.
Small lizards often lay only one
or two eggs, but larger species
like iguanas lay up to 50. The
egg usually has a leathery skin
and gets bigger as the embryo
grows. Gecko eggs are an ex
ception, with shells that harden
and then remain the same size.
Many lizards are extremely fast
runners. The fastest are those
that run on their hind legs, us
ing their long tails for balance.
The racerunner lizard of North
America can run 15 miles per
hour, and the tropical American
basilisk lizard can dash across
the surface of water. In contrast
to these species, chameleons
move slowly.
Many lizards are well adapted
for life in the desert. The Aus
tralian thorny devil as well as
the American horned "toad"
have short, flat bodies covered
with fierce-looking spikes. Their
Left: The basilisk lizard is sometimes called the Jesus lizard because it can run across water.
Some lizards, including many
in cold climates, produce live
young. Outside the body of the
mother, the eggs would perish
in low temperatures. Some spe
cies, like the whip-tailed lizard,
reproduce without mating. They
are all-female species whose off
spring are genetically identical
to their mothers.
coloring and body texture cam
ouflage them in their arid, rocky
habitats. The spikes also have a
cooling function. By increasing
the body surface area, they aid
heat loss and provide surfaces
and channels on which mois
ture from the air can condense.
Other desert lizards cope well
in sandy conditions. The fringe
toed lizard has scaly fringes on
its feet, so it moves easily over
sand. It can also bury itself when
threatened and "swim" under
the sand. Another species that
uses the same tactic is the Ara
bian toad-headed agamid.
Right: The feet of Australia's leaftailed gecko are adapted for gripping smooth surfaces.
~ DIVERSITY Lizards come in many sizes and
shapes. This diversity is the se
cret of their success as an order.
The smallest lizards are geck
os, some of which weigh a frac
tion of an ounce. Geckos have
tiny hairs on their feet, so they
can cling to slight irregularities
on a surface. These "sticky" feet
and a gecko's light weight en
able the lizard to climb appar
ently smooth surfaces and walk
upside down on a ceiling.
At the other end of the scale
Left: The whiptailed lizard is an all-female species of the southwestern United States and Mexico. The offspring hatch from unfertilized eggs and are exact clones of their mothers.
is the jungle-dwelling komodo
dragon of Indonesia. It reaches
a length of 10 feet and a weight
of over 330 pounds. This pow
erful, fast-moving predator can
kill wild pigs and deer.
Chameleons are tree dwellers
that can change color to blend
in with their surroundings. Their
toes, which are separated into
opposed groups, give them a
firm hold on branches. Their
prehensile (gripping) tails pro
vide extra security.
FLIGHTLESS BIRDS
... , ,, 1 • '.. .. ' .. _~ : "'. . " ~ '.' . . . _ .... . • .. _
A bird that cannot fly may seem a contradiction in terms. Yet some birds are better able to exploit their habitats
by keeping their feet on the ground than by flying.
KEY FACTS --------------------------------------------------~
EVOLUTION OF RATITES AND PENGUINS
Ratites appeared 80 million years ago. Different types evolved on each continent when the landmasses separated. The surviving ratite groups are classified in distinct orders, indicating that each group is highly differentiated.
Below: A full-grown rhea can run
I faster than a horse over the pampas of South America.
CONSERVATION
Flightless birds on islands without mammal predators were threatened when settlers introduced livestock, pets, and pests. The birds lacked defenses, and
I their ground nests were vulnerable. One victim was New Zealand's kakapo, and now only about 40 birds remain.
All ratites must have evolved from ancestors that could fly, since they share many characteristics with flying birds. Along with biochemical evidence, the similar bone structures of ratites and weak-flying tinamous from Central and South America suggests that the ancestors of these birds may have been related.
Kiwis have declined since the first Europeans arrived in New Zealand over 150 years ago. Although the brown kiwi and the great spotted kiwi are still widespread on South Island, land clearance poses a threat to the brown kiwi on North Island. To protect the endangered little
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Penguins developed about 70 million years ago and evolved underwater "flight" 45 million years ago. Since then, they have changed little, spending up to three-fourths of their life in icy southern waters.
Below: Using its razor-sharp claws, a cassowary can disembowel an enemy with a well-aimed kick.
spotted kiwi, its population was moved to Kapiti Island in Cook Strait. While its numbers have increased, it is still at risk.
Rheas are hunted for food and for their plumage, which is used for feather dusters. They are also killed because they supposedly damage crops.
The ostrich is not threatened, but many populations have declined because of habitat loss. Cassowaries are at risk due to destruction of tropical forests. Humans have actually helped the emu, which has colonized dry areas in Australia's interior where watering points were set up for cattle and sheep.
Left: The little spotted kiwi has no defenses against mammals that settlers brought to New Zealand.
0160200921 PACKET 92
Some birds became flightless because they lived on
predator-free islands and, as a result, had no need to take
to the air. Others, like penguins, exchanged their wings for
paddlelike structures that helped them "fly" underwater.
Still other birds, such as the ostrich, developed long,
powerful legs on which they could outrun their enemies.
~ WHY FLIGHTLESS BIRDS DEVELOPED The 50 or so flightless bird species alive today all evolved from flying ancestors. Although flight has advantages, it also imposes restrictions. It limits a bird's size and weight, reducing the bird's efficiency in exploiting certain food supplies. In addition, a bird must develop special muscles to fly and keep its plumage in perfect condition. So when there was little benefit from flying, as on islands that had no mammal predators, birds such as the kakapo and many rail species became flightless .
Front cover: The brown kiwi has an excellent sense of smell. It searches for beetles as well as earthworms in soft soil with its long, curved bill.
Front inset left: On land, the appropriately named rockhopper penguin hops with both feet.
Front inset right: The kakapo uses its bill and sharp claws to climb trees.
In the vast, open South American pampas and African savannas, the ostrich and the rheas abandoned flight for greater size. Their long necks and legs let them spot predators at a distance and sprint to safety.
Penguins' wings evolved into "paddles," propelling them underwater. Growing larger and heavier, these birds acquired an insulating layer of fat and conquered the icy Antarctic waters.
Right: Although the emperor penguin is clumsy on land or ice floes, it moves well in the water.
~ FOOD &: FEEDING Flightless birds must generally feed on the ground, but they are good at exploiting the available food supplies. Rheas eat weeds that most other animals avoid, while the ostrich selects the most nutritious plants on the dry plains. Both birds have long digestive tracts that help
~ BREEDING New Zealand once had no landbased predators, so the kakapo could safely nest on the ground . But settlers introduced rats and cats, which stole its eggs.
Many penguins do not use a nest at all. They incubate their eggs between their warm feet and a warm fold of their bellies.
Up to 12 females mate with a dominant male rhea, laying a total of about 60 eggs in his nest. The male then incubates the clutch, and he cares for the chicks for up to six months.
Cassowaries, emus, and kiwis form pairs, but a female cassoLeft: Since a cassowary has a shorter neck and legs than an ostrich, it can forge through dense thickets.
deal with their vegetarian diets. The emu prefers seeds, fruits,
flowers, and young shoots. With its large fat reserves, it can travel hundreds of miles if there is a food shortage.
Penguins feed on prey in the water, diving for several minutes to find their food.
wary may mate with one or two other males after laying her first clutch. The male incubates the eggs and rears the chicks.
A male ostrich loosely bonds with a dominant, "major" hen but mates with up to five other hens. Unlike other ratites, both the male and major hen incubate the eggs. Although these eggs are the largest bird eggs, they are the smallest in relation to the female's size-at about 1.5 percent of her body weight. After hatching, ostrich broods often join up and are guarded by one or two adults. Right: A male ostrich may help incubate dozens of eggs from several females in one nest.
Ratites are large, flightless birds that have lost the large keel on their sternum, or breastbone. In flying birds this bone anchors the powerful flight muscles.
People exterminated two ratite orders: New Zealand's moas and Africa's and Madagascar's elephant birds. The surviving orders contain the ostrich, cassowaries, rheas, emu, and kiwis.
The ostrich, the largest bird in the world, is the only species that has just two toes per foot. It can run over 40 miles per hour and over 60 in short bursts.
Left: When it is in the wild, the flightless kakapo feeds mainly on shrub berries, roots, and grasses. Birds in captivity favor sweet foods as well as fruit.
The two rhea species live in grassland and scrub from Brazil to South America's southern tip. Like the ostrich, they have prominent wings and flap these dramatically when courting.
In Australia the emu lives in open areas, while the three cassowary species dwell in the jungles. Cassowaries possess only remnants of wings.
All four kiwi species are squat, essentially wingless birds that forage in the forests and scrub of New Zealand. Their feathers resemble a mammal's hair.
FROGS AND TOADS
There are nearly 2,700 frog and toad species, making up the bulk of the world IS amphibian species. Most of these creatures go through a larval stage and spend part of their lives in water.
KEY FACTS
CAMOUFLAGE AND SELF-PROTECTION
~ro9S face many predators, and
their thin-skinned bodies offer
little protection against sharp
I claws, teeth, and beaks. To sur
:,ive, frogs use ca~ouflage and, In some cases, pOisonous secre
tions in their skin.
One North American treefrog
is patterned and colored so as
to blend in with rough bark and
patchy lichens. Rainforest frogs,
such as Hyla granosa from Ecua
dor, are frequently bright green,
matching the lush foliage.
The Asian horned frog mimics
the colors and textures of dead
leaves on the forest floor. It even
TOADS
Toads belong to the family Bu
fonidae, one of the 20 frog fami
lies. Compared to frogs, toads
are squat and often seem clum
sy. They are usually warty, with
drier skin than frogs' skin. Many
have short hind legs, which are
better for walking than hopping.
Most toads are dull in color, but
there are exceptions, such as the
European green toad, which has
green and orange markings.
Right: The male midwife toad carries the eggs on his back until they I are ready to hatch.
Left: A poisonarrow frog produces a deadly toxin. Some tribes in South American forests smear this poison on the tips of their arrows and blow darts.
Most toads are active mainly
at night. In the breeding season
large numbers gather at ponds
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Left: The Asian horned frog has flaps of skin, or "horns," that camouflage it among leaves on the forest floor. Horned frogs do not move much, preferring to wait and ambush snakes, lizards, mice, and the oth-er vertebrates that form their staple diet.
has a dead leaf's shape, with flat
points over its eyes and snout.
Frogs that produce dangerous
toxins often advertise this with
brilliant skin colors. Phyllobates terribilis from Colombia is one of
the most lethal, making enough
toxin to kill12 or more people.
Its warning color is bright yel
low or orange.
or other breeding sites. Individ
uals often return to the same
pond year after year.
0160200931 PACKET 93
Frogs and toads can be found in a variety of habitats
throughout the world. They live in swamps, in trees, on
the ground, and even in arid deserts, where they bury
themselves between the infrequent downpours. These
amphibians range in size from a tiny South American
treefrog only a few inches long to the huge goliath frog
of the West African rainforests, weighing over six pounds.
~ EVOlUTION Amphibians-the class between fish and reptiles- were the first vertebrates to move from water to land. Frogs and toads form the largest order of amphibians.
The earliest froglike fossil was found in Madagascar and is 220 to 230 million years old. Called Triadobatrachus, this animal was about four inches long, with a wide, flat skull, elongated hind legs, and a short tail.
The first true frog fossils, called
Front cover: The European treefrog often spends the day perched near water while it soaks up sun.
Front inset left: Like most treefrogs, the South American brown and gold treefrog has adhesive pads at the tips of its fingers to grip branches.
Front inset right: A common frog has reached the adult stage when its tail is fully absorbed.
the" ancient frogs" (Archaeobatrachia) lived some 150 million years ago. The next group, referred to as "middle frogs," appeared 100 to 135 million years ago. The "new frogs," forming the suborder Neobatrachia, date back 50 million years. All modern frog families originated in these three ancient suborders.
Right: Frogs use their strong legs to make a series of springy leaps, while toads crawl.
~ HABITAT Most frogs live near water rath-er than entirely in it. A frog that spends most of its life in water usually has powerful, webbed rear limbs. Its eyes and nostrils are set high on its head, so it can see and breathe with most of its body submerged.
Central and South American treefrogs form one of the largest groups. They are excellent climbers with large, adhesive toe pads that enable them to cling to smooth leaves as well as branches. Rhacophorus nigro
palmatus is a species that can glide from tree to tree. As it
Left: Treefrogs can climb relatively smooth surfaces using their suctionlike toe pads.
Left: Frogs go through a twostage development from the egg to the final adult form. The larval stage, or tadpole, develops in water and feeds on plants.
leaps, this frog spreads out its webbed hands and feet to form a gliding surface.
Spadefoot toads are named for the leathery projections on their hind limbs that they use to burrow backward into the ground. The American spadefoot lives in desert regions and escapes the long months of dry weather by burrowing under the ground. Once the rains begin, the spadefoot comes out of its burrow to spawn. All the developmental stages are then sped up, so the cycle is finished in three weeks.
Right: Frogs do not have clearly defined necks, so their heads seem directly attached to their bodies.
~ lIFECYClE Frogs' eggs lack shells but are protected by a jellylike material. Many frogs lay their eggs in clusters, while some toads lay their eggs in long double strings. In some places frogs make foam nests to protect their eggs. Forest frogs may lay their eggs on leaves overhanging water, so emerging tadpoles fall from the leaves into the pond or stream. Other frogs lay their eggs in specially created mud basins or in small pools. They leave a muddy passage to help the tadpoles reach larger bodies of water, or they carry the tadpoles there.
The egg is fertilized in most species as it emerges from the female. The single cell begins to divide, and the embryo lengthens into the larval stage called a tadpole. The speed of growth depends on the species as well as the climate. When the embryo has developed a mouth,
eyes, and external fishlike gills, it usually hatches from its jellylike casing and continues to develop as a free-swimming tadpole.
Most tadpoles feed on small plant organisms. Some filter water through an internal particle trap. Others are equipped with a horny mouth lining that they use to file organic material from leaves and rocks. Most of a tadpole's body consists of the long, coiled intestine that it needs to digest plant food.
Eventually the hind legs begin to grow out from the body. The tadpole's forelimbs appear from under a flap of skin, and its tail is reabsorbed by the body. Its soft bones harden, while its mouth widens. Increasingly, the tadpole begins to look like a frog. When the tail has disappeared, metamorphosis is complete, although the new frog continues to grow.
HOW MAMMALS SWIM
- -- -- - - - - - - - . - ~--- -
A surprising number of mammals are able to swim. Those that spend all or most of their time in the water have special adaptations that
allow them to swim fast or dive deep for long periods.
KEY FACTS
AQUATIC MAMMALS
Most mammals can swim, but only two groups spend all their time in water. They are the cetaceans (whales, dolphins, and porpoises) and sirenians (the dugong and manatees).
While the pinnipeds are mostly aquatic, they come ashore to breed. This group contains true
I seals, eared seals (fur seals and sea lions, which have small external earflaps), and the walrus.
There are also four-legged, often furred mammal species that
TAIL POWER
Seals swim by moving their rear flippers sideways, but cetaceans and sirenians lack external hind limbs. Instead, they have flat, horizontal tails. Manatees have spade-shaped tails, while other species have fishlike tails.
The animal is propelled by its tail as well as the rear third of its
I DID YOU KNOW? • Blubber is not a soft or jelly-like substance. It is hard like a slab of bacon. • An adult male sperm whale was recorded making a dive of oVer an hour and a half.
are at home on land but spend some of their time in the water, cooling off, grazing, or hunting prey. They range in size from the
body. Its tail and body move up and down, not sideways. Large muscles above the midline impel the upstroke. Smaller muscles, below the midline, pull the tail down. The flukes (two halves of the tail) flex up but not down,
left: The Florida manatee's broad, rounded tail both propels and stabilizes its huge bulk.
• A bull elephant seal has 124 gallons of blood, while a person has less than 5 quarts. • The hippopotamus at times submerges to walk along the riverbed. It sinks or rises to the
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left: Like other sirenians, a manatee is totally aquatic. But it must rise to breathe every few minutes. It is also limited to warm tropicalor subtropical waters.
polar bear and hippopotamus, through medium-size beavers and otters, to the small Pyrenean desman and water shrews.
Left: The flukes of its tail propel the humpback at speeds of up to 17 miles per hour. At times the whale slaps the water, perhaps to stun its prey.
so on the upstroke the tail is fully spread for maximum power.
To lessen resistance, the animal has a streamlined body. Its smooth, firm skin reduces drag. Cetaceans may lubricate their skin to minimize friction .
The front flippers aid steering and balance. Some species have dorsal fins to improve balance.
surface by contracting or expanding its lungs. • The sperm whale has been recorded at a depth of close to 3,760 feet, and it may dive to 9,840 feet.
016020097 1 PACKET 97
Only the fully aquatic mammals have completely conquered
the problems of moving, feeding, and staying warm in water.
However, the ability to swim gives a land-based mammal
certain advantages, including the possibilities of expanding
its range, broadening its diet, and avoiding enemies.
~ ROWING & PADDLING Fur seals, sea lions, and the wal
rus propel themselves with row
ing strokes of their front flippers.
For maximum speed, they also
use their flexible hind flippers
and rear end.
A four-legged, partly aquatic
mammal often does a kind of
"dog paddle." A long tail may
be used as a rudder. However,
the giant otter shrew keeps its
legs close to its body and undu
lates its long, flattened tail.
Limbs and tails are frequently
adapted to maximize their area
in the water. A water shrew has
hairy fringes on its feet and its
Right: Thick skin plus a layer of blubber up to six inches thick keep the walrus warm in Arctic seas.
Front cover: With its flexible neck, the beluga whale can turn sharply.
Front inset left: The South American sea lion swims with a speed and a grace that few other mammals can match.
Front inset right: The hippopotamus enters a river to take the weight off its legs.
tail's underside. The Pyrenean
desman has a long, flattened tail
and stiff bristles on its webbed
feet and partly webbed fingers.
The larger Russian desman can
use its flexible snout as a snorkel.
All beavers paddle with their
webbed hind feet, using their
broad, flat tails as rudders. But
the polar bear-which spends
much of its life in Arctic waters
does not have such adaptations.
~ ECHOLOCATION Underwater visibility is generally
poor, and below 650 feet there
is little light. Like bats, dolphins,
porpoises, toothed whales, and
seals use echolocation to survey
their surroundings, communi
cate, and hunt prey.
~ STAYING WARM Mammals have two adaptations
to keep out the chill of icy water.
Many furred mammals, such as
mink, otters, and muskrats, pos
sess two layers of hair. The long,
water-repellent guard hairs cov
er a dense, fluffy undercoat. The
guard hairs mat together when
wet to form a waterproof "skin"
that traps an insulating layer of
air in the undercoat. Water nev
er reaches the skin. After a few
shakes on land, the animal is dry.
A water shrew does not have
Left: A water shrew traps an insulating layer of warm air in its fine fur when it dives.
The animal emits sound clicks,
each shorter than a millisecond.
If these bounce off an object, the
animal picks up the echo, which
tells it the distance, shape, and
size of the object. It can focus its
clicks on a small fish to pursue it.
long guard hairs but traps air in
its velvety fur. Water eventually
reaches the skin, so when the
shrew lands it runs through a
tight tunnel to wring itself dry.
Truly aquatic mammals lack
fur but have insulating blubber (oil-filled cells) below their skin.
Some whales' blubber is a foot
thick. To regulate its tempera
ture, a whale can open or close
blood vessels in its blubber, let
ting blood flow near its skin if it
needs to cool off.
Right: The common seal's streamlined body enables it to swim and dive rapidly.
~ DIVING Whales must breathe air but can
stay underwater for more than
an hour, and some dive over a
half-mile. While a seal exhales
before it dives, a whale inhales,
diving with a lungful of air.
Pressure at depths below 325
feet causes lungs to collapse, so
the whale stores oxygen in its
blood and muscles. It has a large
Left: The polar bear uses its forelegs to pull itself through the water.
Left: The sleekskinned common dolphin is the fastest of all small dolphins, but it must still surface to breathe.
volume of blood, rich in hemo
globin-a protein carrying dis
solved oxygen. The whale drops
its heartbeat, slowing the flow
of blood, and it can reserve ox
ygenated blood for its brain . It
can tolerate relatively high lev
els of carbon dioxide dissolved
in the bloodstream.
If they surface too quickly, hu
man divers get the "bends," a
condition where dissolved nitro
gen bubbles out into the blood.
To avoid this problem, a whale
has oily foam in its air passages
to absorb the nitrogen. This is
expelled when the whale sur
faces and blows.
Left: The European otter is equally at home in water or on land.
HOW MAMMALS HUNT
Many mammals actively hunt for prey, rather than simply foraging for food. The most specialized hunters are members of the true
carnivore families, which feed almost exclusively on flesh.
KEY FACTS --------~~------- -----~--~----------------~--------------------------~
WHAT MAKES A GOOD HUNTER?
To detect prey, hunting mammals need keen sight, smell, or hearing. They must also be able to move fast, judge distances, seize prey, and quickly kill it. The carnivores, including the dog, cat, bear, weasel, civet, and hyena families, possess many of these hunting characteristics.
Cats are muscular and lithe with quick reflexes. Their long, flexible bodies and strong limbs are suited to bursts of action, rather than long chases. Most cats have sharp, retractile claws. While stalking prey, a cat keeps its claws sheathed, but when it leaps it unleashes them, using them to hold the prey while it attacks with its jaws and teeth.
With short bodies, large rib cages, narrow hips, and long, slender legs, many dog family members are adapted to long
chases, using their stamina to wear down prey. They run on the tips of their toes, aided by blunt, nonretractile claws.
Many weasel family members have long, sinuous bodies and short legs, so they can pursue mice, rabbits, and other prey into their underground tunnels.
A hunting mammal generally has fairly close-set eyes at the front of its skull, giving it binocu/ar(overlapping) vision. This enables it to judge distances and hit its prey when it leaps. In contrast, most prey animals have eyes at the sides of their heads, giving them all-around vision to look out for predators.
Cats have some color vision and keen night vision, with reflective tissue in each eye that maximizes image detection. Their touch-sensitive whiskers
Left: Lionesses are more efficient hunters than lions. But both sexes have long canines set in short jaws, giving them tremendous biting power.
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Above: Before pouncing, the serval listens intently to pinpoint the loeation of its prey.
help in the dark, and they can hear high-frequency sounds, such as small rodents' squeaks.
Dog family members depend mostly on smell to follow prey, often hunting with their muzzles close to the ground. Some foxes and jackals have superb hearing. With its huge ears, the bat-eared fox can hear dung beetle grubs gnawing underground. Other foxes listen for rodents burrowing in snow.
Left: An otter swims as well as the fish it preys upon andean travel 7,300 feet underwater before surfacing. Matted guard hairs covering its coat help keep it warm.
0160200941 PACKET 94
Hunting mammals have evolved specialized techniques
to ensure their survival. Some stalk their prey at night,
while others catch their victims during the day. Some work
in teams, while others hunt alone. Most have sharp teeth
that can cut through flesh strong claws, acute senses, and
muscular bodies capable of sudden bursts of activity.
~ ORIGINS Some of the earliest mammals
ate insects. Instead of actively
hunting, they probably foraged
for prey, scurrying through the
undergrowth and devouring in
sects as they came upon them.
For many millions of years, al l
mammals were foragers, eating
insects, plant material, or both .
The ancestors of today's car
nivores evolved in the Eocene
epoch, 54 to 38 million years
ago. They developed carnassial teeth, which could cut through
animal flesh. All modern carni
vores possess carnassials.
Front cover: The Alaskan brown bear learns by trial and error to seize leaping salmon in its jaws or claws.
Front inset left: The leopard is a wary hunter, looking out for the lions and tigers that will attack it if they can.
Front inset right: Like foxes and jackals, the coyote pounces from a height onto prey.
t -
Left: African wild dogs seize a wildebeest by the upper lip, which seems to tranquilize it. Meanwhile, fellow pack members grab its tail and rear limbs to bring it down.
~ SOLITARY HUNTERS The polar bear is camouflaged
by its white fur, whether it stalks
seals on the ice or crouches by a
hole in the ice, waiting for seals
to rise for air. Many bears, such
as the American black bear and
grizzly, catch fish in the shallows.
They hook prey with their claws
or grab fish with their jaws.
Cats are superb stalkers. They
crouch low and creep slowly,
pause stock-still for minutes if
necessary, and then explode
into a charge or leap. The chee
tah is one of the few cats that
chases its prey. With its long,
Left: The cheetah 5 sinuous, lithe body is suitable for a high-speed chase rather than an ambush.
flexible spine, it can sprint over
60 miles per hour, although it
lacks the stamina for a lengthy
chase. To kill prey, the cheetah
bites it on the throat and holds
on until it suffocates. Specially
adapted nasal passages let the
cat breathe while biting .
Members of the weasel family,
such as otters and mink, can be
ferocious. The weasel, the small
est in the family, can kill a hare
10 times its weight. It mesmer
izes birds by doing spins and
somersaults, then lunges into
the air to seize a victim.
Right: Camouflaged and warmed by its coat, the polar bear waits for seals to surface.
~ TEAMWORK ON THE HUNT The gray wolf hunts in packs. In
forests where deer are the main
food, up to eight wolves hunt
together over a territory of 40
square miles. In the Asian and
North American tundra, gray
wolves hunt for caribou in packs
of up to 20 animals, roaming up
to 400 square miles.
A hunting pack, often in sin
gle file, travels through its terri
tory until it flushes out a lone
quarry or encounters a grazing
herd. The wolves usually corner
single animals. With a herd of
large prey such as musk oxen or
caribou, they harass the group
until panic disrupts its defensive
formation. The wolves then iso
late a vulnerable animal, such as
an old adult or a calf.
The African wild dog is an ex
pert in hunting cooperatively.
Packs of 6 to 30 dogs cover up
Left: In a team effort, some lions hide downwind, while others herd prey into the ambush.
to 30 miles per day, searching
for prey. The dominant breed
ing pair leads the hunt, usually
at dawn or dusk. After selecting
a victim, such as a gazelle, and
separating it from the herd, the
wild dogs wear it down by their
speed and stamina . They can
keep up the chase for 3 miles at
a speed of almost 40 miles per
hour. The wild dogs attack the
tired animal from both ends,
bringing it to the ground and
quickly disemboweling it.
Lions hunt as a team. When
they move in on a herd of prey,
they may spread out in a line to
intercept strays. Often the males
roar, so the herd panics, splitting
and fleeing in all directions.
Chimpanzees may also work
in teams to capture a monkey.
They chase their prey through
the branches and force it to take
risks until it is cornered or falls to
the ground, where other chim
panzees trap it.
Marsupials range from tiny shrewlike animals to kangaroos. Barely developed at birth, the young live on their mother's milk for up to a
year and a half and are often protected in a special pouch.
KEY FACTS
AMERICAN MARSUPIALS
1 0 large marsupials remain in the Americas. The surviving species are mainly in the opossum family. Most are good climbers, with well-developed digits and a thumblike big toe. They usually have prehensile tails, which they curl around branches when climbing. Some, such as the Patagonian opossum and several mouse opossums, can store fat in their tails if food is scarce.
The Virginia opossum of Central and North America eats any-
I thing from fruit to city garbage. The largest American opossum, it can be over three feet long . In contrast, the Formosan mouse
opossum of Argentina measures about five inches.
The water opossum, the only truly aquatic marsupial, uses its webbed hind feet to swim. The entrance of the female's pouch closes to keep water out when
SMALL MARSUPIALS OF AUSTRALIA AND NEW GUINEA
The most numerous marsupials in Australia and New Guinea are probably the dasyures, a family of primarily small flesh eaters. A number of them resemble mice or shrews, with pointed snouts for digging up insects and small but sharp teeth .
The fierce, carrion-eating Tas-
man ian devil is the biggest dasyure. The spotted-tailed native cat is almost as large. It prefers live prey such as wallabies and some reptiles .
Bandicoots, phalangers, and gliders also live in this area. Bandicoots have thickset bodies and dig up worms and grubs with
© MCMXCII IMP BV/IMP INC WILDLIFE FACT FILETM PRINTED IN U.S.A
Left: The lutrine water opossum nests in reeds at the riverside. It is a strong swimmer, lashing its tail like a whip from side to side and paddling with its hind feet.
she submerges to find fish, crustaceans, and frogs.
Shrew or rat opossums live in the Andes. Usually less than 31 inches long, they are most active at night, foraging on the ground for insects or small vertebrates.
their three-toed forefeet. The brindled bandicoot may have the shortest gestation of any mammal (12~ days).
Phalangers have big eyes and gripping tails . Most are nightactive tree dwellers . New Guinea's cuscuses possess tiny ears and dense fur. Brush-tailed possums in Australia and New Zealand have larger ears.
The sugar glider and its relatives live in forests and eat fruit, leaves, gums, pollen, sap, and nectar. Using skin membranes between their limbs, they glide from tree to tree.
The marsupial mole has a cylindrical body, blunt snout, short but strong legs, and sleek, pale brown fur. It uses its sturdy claws to burrow and eats insect larvae.
Left: A tough plate on the marsupial mole's nose protects it as it digs.
0160200981 PACKET 98
Marsupials are found mainly in Australia, New Guinea,
and the Americas. They include grazing species, such as
kangaroos; fruit and nectar eaters, like woolly opossums;
and flesh eaters, such as the spotted-tail native cat and
Tasmanian devil. Marsupials are adapted to a variety of
different environments, with opossums climbing in trees
and the marsupial mole burrowing in the ground.
~ ORIGINS Some 100 million years ago, the marsupial and placental mammals diverged . Placentals developed a system of nurturing their young inside the female's body, while marsupials gave birth to embryonic offspring and then nursed them outside of the female's body, usually in a pouch.
The oldest fossils of marsupials come from 75-million-year-old rocks in North America. Those animals spread into what is now South America. Then the landmasses separated. Marsupials in North America, unable to com-
Front cover: The koala is a peaceable tree dweller.
Front inset left: The sugar glider "flies" between trees.
Front inset right: Most newborn marsupials suckle for some time in their mother's pouch.
pete with placenta Is, died out. Isolated from placentals, mar
supials in South America evolved freely for 60 million years. Two to five million years ago, a land bridge reunited the two Americas. Placental mammals moved south, and the big marsupials became extinct. Smaller marsupials survived, and some even went north. Today the Virginia opossum is the most common North American marsupial.
The earliest marsupials in Australia date back some 32 million years. They probably reached there via Antarctica, which connected Australia to the Americas. In time Australia split away and drifted north, remaining isolated from other landmasses. Its marsupials evolved without competition into a range of creatures.
Numbat: Lives in the woodlands of southwestern Aus
tralia . It employs its claws to dig out termite colonies, extract ing the insects with its
tongue. Since the female lacks a pouch , she keeps
her litter in a burrow.
~ THE LARGE MARSUPIALS The best-known Australian marsupials are the koala, wombats, kangaroos, and wallabies. The koala and wombats have some similarities, but the koala lives only in trees, while wombats live in burrows. The koala finds all its food in the trees, eating the leaves of about 20 species of eucalyptus. The female bears one offspring every two years. It lives in her pouch for 7 months and then travels on her back, finally leaving her at 11 months.
Wombats are squat and powerful, using their long claws to dig burrows as long as 100 feet. They rest underground to avoid the daytime heat and emerge to feed on grasses after dark.
Kangaroos and wallabies are, respectively, big and small members of the .same family. While they are related to kangaroos, rat kangaroos are much smaller and belong to a separate family.
Some prehistoric kangaroos were huge-1 0 feet high. The largest marsupial today is the red, or plains, kangaroo. Some males are over 5 feet tall and weigh about 200 pounds. The red kangaroo is widespread in Australia's dry flatlands. Preferring to travel in groups, it can leap 5 feet with a slow hop and over 13 feet in a hurry. Males can move 40 miles per hour.
Other kangaroos include gray kangaroos, which inhabit forest
~ BREEDING Marsupials get their name from the Latin marsupium, meaning "pouch." Most have some sort of pouch in which their young develop. In some, such as a kangaroo, it opens forward . In others, such as the koala, it opens to the rear.
Compared to placental mammals, marsupials have a very
Western gray kangaroo: One of the largest marsupials. After leaving the pouch, the joey (young) returns for milk, suckling at a "personal " teat that yields the correct milk composition .
Tasmanian devil: Weighs up to 18 pounds and reaches three feet in length .
and scrubland. They sleep in the shade during the day and come out at dusk to graze.
The whiptail wallaby lives on grassy hillsides, where it grazes in groups of about 50 animals. The swamp wallaby is at home in marshy country on the eastern coast, while the brush-tailed rock wallaby hops among rocks and cliffs in the mountains of New South Wales, employing its long, slender tail for balance.
One of the smallest true kangaroos is the quokka. About the size of a hare, it has a squat body with short ears. It inhabits the swamps and thickets of Australia's southwest coast and one or two small islands.
short gestation. Opossums are born in only 12 to 14 days, phalangers in 16 to 17 days, koalas in 34 to 36 days, and kangaroos in 36 days at most.
The newborn is hairless, blind, and embryolike with only crude limbs. As it makes its way to the pouch, it sometimes follows a track of fur licked down by its mother. After it is inside, it sucks on a nipple that swells to fill its mouth and remains securely attached for several months. The pouch protects the offspring, so
It eats mainly dead flesh , using its powerful jaws and large teeth to rip carcasses apart and crunch up bones. It has been known to steal poultry and lambs from ·farms.
Mouse opossum: The 47 species vary greatly in their diets, climbing abilities, and habitats. The young cling to their mother, since she lacks a pouch .
it can reach a well-developed stage before facing the dangers of the outside world .
In some kangaroo species, the mother mates shortly after giving birth. But the fertilized egg remains in her body and only develops after the first offspring has left her pouch . The young kangaroo goes out for brief periods at first, leaving the pouch for good at 5 to 11 months old. It may stay with its mother for another 2 to 6 months, suckling from outside the pouch .