The word “mammal” derives its origins from the Latin “mamma” which refers to animals with mammary glands. This is one of the most distinctive and most important traits of these animals. They nourish their young with milk from their mammary glands and take care of them after they have developed inside their bellies. These animals also have hair, even if it is sometimes only present in the embryonic state. This group includes more than 4000 species that have adapted to a wide variety of environments. They can be found on the ground (rodents and ruminants, etc.) as well as in aquatic or marine environments (whales and seals, etc.) as well as in the air (bats).