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, arewarm-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!
Scientists divide mammals into three groups.
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.
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 likeTyrannosaurus 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 everyenvironment. 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 pandasand tigers. Europe and North America have bears and deer. Australia is the only continent that has egg-laying monotremes and marsupials.
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.
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.