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Amphibian • Bird • Fish • Insect

• Living Things • Mammal • Mollusk

• Plant • Reptile •Worm

Animal Disease

#see Disease, Animal.

AnimalMigration

#see Migration, Animal.

Animals, Extinct

When an entire species, or type, of animal

dies out, that species is extinct.

Once a species becomes extinct, it is

gone forever.

Causes of Extinction

The most common cause of extinction is

a sudden, serious change in a species’

habitat. A habitat is the surroundings in

which an animal lives. Animals can

rarely survive such sudden change. Their

food supply may be wiped out. They

may also lose shelter or other things that

they need to survive.

Many things can change a species’ habitat.

Floods, fires, droughts, volcanoes,

and other natural events may be causes.

People also change the environment in

ways that drastically affect animals.

People clear forests and drain wetlands.

They build dams that disrupt the flow of

rivers. They build cities on land that

animals need to survive. They also create

harmful pollution.

Some changes that cause extinction

affect only a small area. Others are large

enough to affect the entire world. A fire

or other local event may cause the

extinction of animals that live only in

that region. A sudden change in the

global climate might wipe out an animal

species that lives in many parts of the

world.

People can cause extinctions more

directly as well. Some species have been

hunted to extinction. The passenger

pigeon is one example. Humans killed

millions of the birds over many years.

The last one died in the early 1900s.

Mass Extinctions

Sometimes many different species

become extinct in a short time. This is

A bird called the dodo once lived on an

island in the Indian Ocean. Europeans took

control of the island in the 1500s and

began to hunt the bird. By 1681 the dodo

was extinct.

126 Animal Disease BRITANNICA STUDENT ENCYCLOPEDIA

 

called a mass extinction. Several major

mass extinctions have occurred in the

past. Each time many animal species

were wiped out. Some survived, however,

and over millions of years new species

developed.

The worst mass extinction happened

about 248 million years ago. This

extinction included mainly animals

without backbones that lived in water.

Another mass extinction occurred about

65 million years ago. It wiped out many

of the planet’s land animals, including

the dinosaurs.

Dinosaur Extinction

Dinosaurs first appeared on Earth about

215 million years ago. They were the

most important land animals for more

than 150 million years. By 65 million

years ago, however, the dinosaurs had

died out.

Many scientists believe that a large asteroid,

or rock from space, caused this mass

extinction. When the asteroid hit Earth,

the impact caused drastic changes. Thick

dust and other materials blocked the

sun. Temperatures dropped, and plants

could not grow. The dinosaurs could not

survive the cold temperatures and lack

of food. But early species of birds and

mammals did survive.

Large Mammal Extinction

About 10,000 years ago another mysterious

animal extinction occurred. This

extinction was especially dramatic in

North America, where many large mammals

disappeared. Among them were

woolly mammoths and saber-toothed

cats.

Scientists do not know what caused this

extinction. Some believe that growing

numbers of human beings hunted and

killed too many of the animals or their

prey. Another theory is that the climate

changed and affected the availability of

food.

Endangered Species Today

In the past 200 years the world has lost

many animal species. Hundreds of others

are on the verge of extinction. Animals

at risk of dying out are called

endangered species.

Governments today are working to protect

the world’s endangered species.

Laws protect some animals’ habitats

from being polluted or destroyed. Other

laws make it illegal to hunt endangered

animals. Some species respond well to

these protective measures and increase in

number. Others are not as successful.

#More to explore

Animal • Dinosaur • Endangered

Species • Mastodon and Mammoth

The Carolina

parakeet and

the passenger

pigeon were

birds once

found in the

United States.

People killed

so many of

them that both

types became

extinct in

1914.

The Tasmanian wolf is an extinct animal.

The last members of the species died out in

the 1930s.

BRITANNICA STUDENT ENCYCLOPEDIA Animals, Extinct 127

 

Animals,

Legendary

Stories about unusual animals were

commonplace in earlier times. Such

animals are called legendary because

they exist only in these stories, or

legends. The stories were often based on

travelers’ reports of animals that were

unfamiliar to them. Some famous

legendary animals include the dragon,

various sea serpents, the unicorn, and

the phoenix. Even today some people

speak of having seen animals such as

the yeti, Bigfoot, and the Loch Ness

monster.

The Dragon

The dragon was usually thought of as a

huge scaly lizard or snake that breathed

fire and had wings like a bat. In the

Middle Eastern world, the serpent or

dragon symbolized evil. In Christian art

the dragon came to stand for sin. In

China, however, the dragon is known as

a kind creature.

Sea Creatures

Sea serpents were supposed to be

enormous snakes, or huge creatures that

inhabited the deep sea. Sailors

throughout the ancient world reported

having seen such creatures. In

Norwegian sea folklore, the kraken was

a huge creature, part octopus and part

crab. Accounts of these creatures might

have been based on sightings of giant

squid, which can reach a length of 60

feet (18 meters).

Mermaids were also mythical sea creatures.

They were thought to have the

head and upper body of a woman and

the tail of a fish. Stories of mermaids

may have come from people who saw

water-dwelling mammals, such as the

dugong and manatee. These animals

feed their young in human fashion

A sculpture of a dragon decorates a tiled

wall in Beijing, China.

Mermaids have appeared in many stories,

including “The Little Mermaid” by Hans

Christian Andersen.

128 Animals, Legendary BRITANNICA STUDENT ENCYCLOPEDIA

 

above water and from afar may have

looked like a person.

The Unicorn

The unicorn was a mythological animal

with a single horn on its forehead. Its

body shape resembled a horse or a

young goat. The unicorn was referred to

in the ancient myths of India and

China. It appears in artwork from the

ancient civilization of Mesopotamia.

During the Middle Ages (about AD 500–

1500) artists from Europe, the Islamic

world, and China included the unicorn

in their artwork as well.

The Phoenix

Mythological creatures also have taken

the form of birds. A fabulous bird

known as the phoenix was associated

with the worship of the sun in ancient

Egypt. It was said to be as large as an

eagle, with brilliant scarlet and gold

feathers. Legend had it that only one

phoenix existed at any one time and

that it lived at least 500 years. As its

death approached, the phoenix made a

nest. It then set the nest on fire and