Mammals are animals that feed their young ones with . They live in all regions of the world. Mammals are different than other creatures in many ways. They have or hair-like skin and their body temperature always stays the same. Mammals, especially , have a that is well-developed. They protect their babies and prepare them for future life.
Through the ages many mammals have been . Some are kept as pets, others are used to doing heavy work , like ploughing the fields or transporting goods. Some mammals are hunted by who sell their valuable body parts.
Female mammals carry babies in their bodies until they are born. After birth, produce milk to feed the small ones. In some cases newly born mammals can walk or run alone shortly after birth.
Plant-eating mammals , or , have a complicated digestive system with long . Meat-eaters do not chew so much. The food passes through their body more quickly.
Mammals have a widely developed range of . Bats, for example, use their hearing sense to find their way around. Humans and apes can see very well. Cats have with which they feel through darkness.
Marsupials are Australian mammals that carry their babies in in their skin until they are ready to live alone. Kangaroos and belong to this group. Only few mammals lay eggs, from which babies . The and echidna belong to this group.
Some mammals , like squirrels, during the cold part of the year because they cannot get enough food during the wintertime. Others to other areas in order to survive. Arctic whales, for example, travel to the warm waters of the Californian coast to have babies, because they would not be able to in the cold waters of the north.
The first mammals appeared during the Mesozoic era. They were small at first . After the dinosaurs died out about 65 million years ago mammals became bigger and bigger and ruled the continents. During the Ice Age many mammals, like the , became extinct.