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 planets 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 worlds 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