The World of Mammals


A mammal is an animal that feeds its babies with milk when it is young. There are over 4,500 types of mammals. Many of the most popular animals we know are mammals, for example, dogs, cats, horses, cows, but exotic animals like kangaroos, giraffes, elephants and anteaters belong to this group, too. Humans are also mammals.

Mammals live in all regions and climates. They live on the ground, in trees and even underground. Polar bears, reindeer and seals are mammals that live in the Arctic regions. Others, for example camels or kangaroos, prefer the world’s dry areas. Seals and whales are mammals that swim in the oceans; bats are the only mammals that can fly.

Colony of seals
Image: M. Boylan [Public domain]

Mammals have five features that make them different from other animals:

  • Female mammals produce milk and feed their babies with it.
  • Only mammals have hair or hair-like skin. All mammals have hair at least some time in their lives.
  • Mammals are warm-blooded. Their body temperature always stays the same and does not change with the outside temperature.
  • Most mammals have a larger and well-developed brain. They are more intelligent than other animals.
  • Mammals protect their babies more than other animals. They prepare them for future life.

People have hunted mammals for ages.They ate their food and made clothes out of their skins. Thousands of years ago wild mammals were domesticated and gave human beings milk, wool and other products. Some mammals, like elephants and camels, are still used to transport goods. In poorer countries farmers use cows or oxen, to plough fields.

Animals ploughing fields in India
Image: © Yann Forget / Wikimedia Commons / CC-BY-SA

Today some mammals are hunted illegally. Whales are killed because people want their meat and oil, elephants are killed for their ivory and tusks.

Mammals are often kept as pets. Among them are cats, dogs, rabbits or guinea pigs.

Mammals are useful to people in many other ways. Some help plants grow and eat harmful insects. Others eat weeds and prevent them from spreading too far. The waste of mammals is used as fertilizers that improve the quality of soil.

Tusk of an African elephant
Image: Taken by Schuyler ShepherdCC BY 2.5, via Wikimedia Commons

History of Mammals

The first mammals probably evolved from reptiles about 200 million years ago during the Mesozoic period. They were rather small in a time when dinosaurs ruled the lands. When the dinosaurs died out about 65 million years ago mammals became the dominant land animals. Many mammals became extinct during the Ice Age , which ended thousands of years ago.

Today, some species are in constant danger of becoming extinct because they are hunted by humans. Hunters and poachers earn money by selling fur, tusks and other parts of mammals. Larger wild animals are often brought to zoos where they are protected.

Artist’s image of wooly mammoths during the Ice Age
Image : Charles R. Knight, Public domain, via Wikimedia Commons

Types of Mammals

Mammals are divided into three groups:

  • Monotremes are mammals that lay eggs, like a bird. They live in Australia and New Zealand. The platypus belongs to this group.
  • Marsupials are mammals that raise their young ones in a pouch in their bodies.
  • Placentals are the largest group of mammals. The babies grow inside their mothers until they are ready to be born. Humans are placentals.

Image:Stefan KraftCC BY-SA 3.0, via Wikimedia Commons

Bodies of Mammals

Skin and hair cover a mammal’s body. Some mammals have horns, claws and hoofs. The hair or fur of a mammal has many functions. The colour often blends in with the world around them and allows them to hide from their enemies. Some mammals produce needles or sharp hair that protects them from attack. But the main function is to keep the body warm.

Mammals have glands that produce substances that the body needs like hormones, sweat and milk.

A mammal’s skeleton is made up of three parts:

  • The skull contains the brain, teeth and other organs.
  • The spine or backbone enables mammals to stand or walk.
  • Limbs are legs and arms of a mammal, often with strong bones.

Mammals have a four-chambered heart system that pumps blood into all parts of their body. The blood brings oxygen to muscles and tissue. The red blood cells of mammals can carry more oxygen than many other animals. Because mammals have a high body temperature they must burn a lot of food.

Mammals digest food through their digestive system. After food is eaten through the mouth it goes down the throat into the stomach and passes through the intestines. Mammals that eat plants have a complicated system with long intestines that help break down food. Flesh is easier to digest so meat-eating mammals have a simpler stomach.

Mammals breathe air through their lungs. Most of them have noses or snouts with which they take in air. Dolphins and whales breathe through a hole in the top of their back.

The needles of a hedgehog
Gibe [CC BY-SA 3.0], via Wikimedia Commons

A deer is a plant-eating mammal
Alastair Rae from London, United Kingdom [CC BY-SA 2.0], via Wikimedia Commons

Whales breathe through holes on top of their heads
AWeith [CC BY-SA 4.0], via Wikimedia Commons

Mammals and Their Senses

Mammals have five senses that tell them what is happening in their surroundings. Not all senses are developed equally among mammals.

Mammals rely on a sense of smell to find food and warn them of their enemies. Many species use smell to communicate with each other. Humans, apes and monkeys have a relatively bad sense of smell. Taste helps mammals identify the food that they eat.

Most mammals have a good sense of hearing. Some mammals use their hearing to detect objects in the dark. Bats, for example, use sounds to navigate and detect tiny insects. Dolphins also use such a system to find their way around.

While higher primates, like humans, apes and monkeys have a highly developed sense of sight other mammals are nearly blind. Most of these mammals, like bats, are active at night.

Mammals have a good sense of touch. They have nerves in all parts of their body that let them feel things. Cats and mice have whiskers with which that they can feel themselves around in the dark.

The whiskers of a cat help them feel things
Image:  Wolf ReynoldsCC BY 3.0, via Wikimedia Commons

What Mammals Eat

Herbivores are mammals that eat plants. They have special teeth that allow them to chew food better. Examples of herbivores are deer, cows and elephants. The giant panda is a plant eater that only eats bamboo.

Carnivores are mammals that eat other animals. Cats, dogs, tigers, lions, wolves belong to this group. They are hunters that tear their prey apart with sharp teeth. They do not chew their food very much.

Omnivores are mammals that eat plants and meat. Bears, , apes, pigs and humans are examples of omnivores.

Giant Panda eating bamboo
Image: Chi KingCC BY 2.0, via Wikimedia Commons

How Mammals Move

Most mammals live and move on the ground. They have four legs and walk by lifting one foot at a time or by trotting. Kangaroos hop and use their tail for balancing.

Mammals that live in forests spend a lot of their time in trees. Monkeys can grasp tree branches with claws and can hang on to them with their curved tail. Mammals often spend time hanging upside down in trees.

Dolphins and whales are mammals that live and move around in water. Instead of limbs they have flippers which they use to move forward. Other animals, like the hippopotamus, only spend some time in the water.

Bats are the only flying mammals. Their wings are made of skin stretched over their bones. They can fly by beating their wings up and down.

Gophers and moles are mammals that spend most of their life underground.

Monkeys hang around in trees most of the time.
Image:  Dmitry MakeevCC BY-SA 4.0, via Wikimedia Commons

Gophers live underground most of the time
Image: LeonardoWeissCC BY 3.0, via Wikimedia Commons

How Mammals Reproduce

Mammals reproduce when a male’s sperm gets into contact with a female egg and fertilizes it. A young mammal grows inside the female’s body. Before this can happen mammals mate. Males and females stay together for a certain time.

Unborn mammals live in their mother’s body for different periods of time. While hamsters are born after only 16 days, it takes elephants 650 days to give birth. Human pregnancies last about 9 months. Many new-born mammals, like horses and camels, can walk and run shortly after they are born.

Marsupials give birth to babies that attach themselves to their mothers. They stay in pouches because they are too weak to live alone. Almost all marsupials, including kangaroos, koala bears or wombats live in Australia .

After birth, the glands of female mammals produce milk. Some mammals nurse their babies for only a few weeks. Others, for example elephants, give milk to their babies for a few years.

The duck-billed platypus and echidnas are the only mammals that lay eggs. After the young hatch they drink milk from their mother, just like other mammals do.

Lions mating in Africa
Image: Christopher MichelCC BY 2.0, via Wikimedia Commons

Mother nursing a young horse
Image: AdamantiosCC BY-SA 4.0, via Wikimedia Commons

Life Habits of Mammals

Many mammals live in families or groups. Wolves and lions help each other in their search for food and protect each other from attackers. Leopards, cats, tigers and other mammals prefer living alone . They do not share their living space and food that they have, however males and females get together to mate. Mammals can mark the areas that they live in. They defend these areas by fighting off attackers. Some mammals claim territories only during the breeding season.

Many mammals migrate during special times of the year in order to get food and survive. North American bats travel to the south because insects become scarce during the cold winter months. Zebras and other wild animals follow the rainy seasons in Africa to find green grass. Whales migrate to warmer southern waters off the coast of Mexico to give birth to babies because they can not survive in the cold waters of the Arctic Ocean.

Some mammals hibernate because they cannot find enough food to survive. Their body temperature falls, heartbeat and breathing become slower. During this period hibernating mammals do not eat. They live from the fat of their bodies. Bats, squirrels and other rodents hibernate.

Mammals defend themselves from attackers in many ways. Hoofed mammals can run quickly in order to get food or escape. Squirrels rush into trees to hide. Some animals have special features that protect them from enemies. Skunks spray a bad smelling liquid to keep off attackers. The fur of mammals sometimes changes with its surroundings. Arctic foxes, for example, are brown in summer and in the winter their coats turn white.

Herds of zebras migrating in eastern Africa
Richard Mortel from Riyadh, Saudi Arabia [CC BY 2.0], via Wikimedia Commons

Arctic fox
Erik F. Brandsborg from Oslo, Norway [CC BY-SA 2.0], via Wikimedia Commons



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