Why Do Mammals Have Fur?: And Other Questions About Evolution and Classification
What is a mammal Mammals are warm blooded animals This means that they can keep their bodies at the same temperature by burning food to keep warm Mammals breathe air and most have hair on their bodies Mammal mothers all produce milk to feed their babies This mammal like reptile named Estemmenosuchus lived 255 million years ago How mammals evolved Mammals are descended from mammal like reptiles that lived around 260 million years ago Most of these creatures had died out by the start of the Mesozoic era the age of the dinosaurs but a few survived and developed into the first true mammals The first true mammals were similar to modern day shrews The first mammals The first real mammals were shrew like animals that lived alongside the dinosaurs and probably ate insects Because they were warm blooded they were able to hunt at night when the cold blooded dinosaurs were asleep The little mammals developed good senses of smell and hearing so they could find their prey in the dark TIMELINE CENOZOIC ERA MESOZOIC ERA 252 66 million years ago mya Paleocene 65 56 mya Eocene 34 56 mya
23 5 5 1.8 1.8 10,000 10,000 Holocene Pleistocene Pliocene Miocene now ya ya mya mya mya mya 23 34 Oligocene Mammals inherit the Earth At the end of the Mesozoic era a catastrophic event wiped out all the dinosaurs Most scientists believe that an asteroid struck the Earth and sent up a huge cloud of dust which blocked out the Sun so plants could not grow Without competition from the dinosaurs the little mammals quickly evolved into many different groups THE AGE OF MAMMALS Mammals are the only animals that suckle their babies Smilodon is one of the best-known saber-toothed cats It lived during the Pleistocene epoch 30 20 10
Classification of mammals There are more than 5,000 species of living mammals They are divided into about 21 groups As well as those shown below there are other groups made up of just one or two species These are the colugos flying lemurs aardvarks hyraxes and elephant shrews Even-toed hoofed animals These mammals carry their weight on their third and fourth toes They include deer pigs cows sheep hippos and giraffes Whales dolphins and porpoises These mammals called cetaceans have adapted to a life spent entirely in water making them one of the most highly specialized groups Odd-toed hoofed animals Bats This group includes horses zebras rhinos and tapirs They carry most of their weight on their third toe Carnivores The meat-eating mammals differ in size more than any other group They include weasels cats dogs and bears 6 Bats are divided into megabats which eat fruit and nectar and do not have echolocation and microbats that use echolocation and feed on insects Insect-eaters Insectivores survive mainly on protein-rich insects and worms This group includes hedgehogs moles and shrews
Rodents More than 40 percent of mammals are rodents Their teeth never stop growing so they need to gnaw constantly to keep them short Sea cows Dugongs and manatees make up this group of aquatic mammals that graze on sea grass and other underwater plants Rabbits hares pikas These mammals are similar to rodents Their teeth grow all through their lives but unlike rodents they have two extra peg teeth behind their top incisors Pangolins Pangolins are the only mammals that have scales instead of fur They use their long claws to dig up anthills and termite nests for food Primates Primates have eyes that face forwards and most have five fingers and toes with opposable thumbs They include monkeys apes lemurs and humans Elephants African and Indian elephants are the only surviving species from a group of mammals with trunks that included the woolly mammoth Fin-footed mammals Seals sea lions and walruses are semi-aquatic adapted to living on land during the breeding season and spending months at sea Sloths anteaters and armadillos Only found in the Americas these mammals had huge prehistoric relatives the giant ground sloths and the tank-like glyptodonts Marsupials Marsupials give birth to undeveloped babies that grow in their mothers pouches instead of inside their bodies They include kangaroos koalas and opossums Monotremes The duck-billed platypus and the echidna are monotremes They are the only mammals that lay eggs but they still feed their babies on milk 7
