The Wild World of Mammals
Humans share one trait with many of the most
familiar animals on Earth. We are mammals. You probably recognize many more
mammals than you think. Some familiar mammals are bears,
elephants, horses, primates, foxes, squirrels, kangaroos, rhinoceroses,
cats, whales, dogs, and mice.
People are one of the most common mammals on Earth. There are more than
6 billion of us, living in every environment.
©G.Ellis/GLOBIO.org Some, like aardvarks, colugos, echidnas, aye-ayes, tamanduas, and uakaris
are much less familiar, but they have great names! Mammals get their name from
the fact that the females produce milk for their babies from special glands
called mammary glands. All 4,150 species of
mammals have backbones, are warm-blooded,
have a skin covering of hair or fur, and need to breathe air. The largest mammal
is the blue whale, which is over 30
m long and weighs 91
metric tons. The smallest is the bumblebee bat. It is only 3.1
cm long and weighs 2
g!
Three Groups
Scientists divide mammals into three groups.
An echidna is a type of monotreme mammal. Monotremes hatch from eggs.
©G.Ellis/GLOBIO.org The first group is the monotremes.
These unusual mammals live in Australia and New Zealand and lay eggs just
like a bird.
Wallabies are marsupials. Marsupial babies live inside a soft, warm pouch
while they grow and develop.
©G.Ellis/GLOBIO.org The second group is marsupials.
Kangaroos and koalas who raise their young in an outside pouch are marsupials.
African lions are placental mammals that give birth to their cubs in litters
of three to four. They live in family groups called prides.
©K.Campbell/GLOBIO.org The largest group is the placentals.
Members of this group have young who develop fully inside the mother until
they are ready to be born. Humans belong to this group of mammals.
Early Mammals
Mammals began evolving millions
of years ago. The earliest mammals were tiny and mouse-like. It was good to
be small then, because mammals had to share Earth with very large dinosaurs
like Tyrannosaurus rex. Today, we find mammals in a wide variety of
sizes, shapes, and behaviors. They range from bats that fly through the air
to moles that spend much of their lives underground.
Mammals, Mammals Everywhere
Koalas are one of the many marsupials found only in Australia. Their babies
grow inside a pouch and are called joeys.
©G.Ellis/GLOBIO.org Mammals live in almost every environment.
The center of Antarctica is the only area off limits to mammals. Every continent
has its own collection of interesting mammals. Africa has lions, giraffes,
and zebras. Asia has giant
pandas and tigers. Europe and North America have bears and deer. Australia
is the only continent that has egg-laying monotremes and marsupials.
Mammal Menu
Mammals eat a wide variety of foods. Humans
and rats are mammals that are omnivores,
meaning they eat many types of food. But most mammals specialize in eating
one type of food. Insectivores only eat insects. Herbivores only
eat plants, and carnivores eat
only meat. Giant
pandas are built like carnivores but act like herbivores and have a very
limited diet. They eat almost nothing but bamboo.
Anteaters eat only ants and termites. The blue whale, the biggest mammal of
all, eats tiny 3
cm-long shrimp called krill.
Mammal Anatomy
All mammals have the same basic internal
parts. Their structure is supported by a backbone, or vertebral
column, as well as many other bones. In the chest are vital organs like
the heart and lungs. The abdomen contains the stomach, reproductive organs,
and waste disposal organs.
Click below to explore similar mammal bodies.
©G.Ellis(tiger)/GLOBIO.org;
M.Durham(bat)/GLOBIO.org; C.Newbert(whale)/Minden Pictures Discovering New Mammals
This rare night photograph shows a newly discovered mammal. The new mammal
is bigger than a domestic cat. It is dark red and has a long muscular tail.
The photo was taken by biologist Stephan Wulffraat.
©Stephan Wulffraat Discovering a new species of mammal, especially
a large one, is very rare these days. However, in December 2005, scientists
discovered a new cat-fox mammal in the tropical rainforest on the island of
Borneo. The creature, believed to be carnivorous, was spotted in the Kayan
Mentarang National Park, which lies in the Indonesian territory of Kalimantan
on Borneo. Scientists say urgent conservation is needed to protect the forests
in Southeast Asia, which are being lost due to logging and the palm oil trade.
The 2
million hectares of rainforest where the new mammal was discovered is planned
to be cut soon to make way for palm oil plantations.