What is a mammal?
We’re all familiar with mammals – when you ask people to think of an animal, they’ll typically mention mammals first – cats, dogs, horses and so forth. We are more familiar with mammals than with other kinds of animals, even though there are only 5400 different types of mammal, compared with, say, millions of different types of insect!
Here are some of the things that define an animal to be a mammal. First of all, mammals are vertebrates, so like all vertebrates,
- Mammals have bones, especially a backbone
- They mostly have a tail and a hollow mouth
Mammals differ from other vertebrates as follows
- Mammals give milk to their babies – we all know that cows give milk. In fact all mammals give milk – cats, mice, bats – even the long-beaked echidna or the humpback whale!
- Mammals have skin and hair – although some whales only have hair before they are born.
- Mammals keep their body at (more or less) a constant temperature. Birds also do this, but reptiles, amphibians and fish do not.
In addition, almost all mammals have exactly 7 neck bones, a heart with four chambers, and the outer layer of the mammal’s brain has a special layered structure. Compared with other animals, mammals learn a lot more from their parents, are more intelligent, and also need to eat a lot.
In case you hadn’t guessed it, people are a kind of mammal too!
What is the world’s biggest mammal?
Some of the world’s biggest animals are mammals. The world’s biggest ever animal is a mammal, the Blue Whale! This enormous creature can grow as long as seven cars, and weigh more than a Boeing 747 jet airplane! The tallest and the heaviest living land animals (the Giraffe and the African Bush Elephant ) are also mammals!
What kinds of mammal are there?
There are about 5400 different types of mammal. Mammals form a group of animals called a Class, which scientists call Mammalia. This class is split into smaller groups, called Orders. Scientists are still debating on exactly what these groups should be, but the list below is reasonably close to a “standard” list
- The Monotremes are a very small group of very unusual mammals. They include the platypus and echidna of Australia. The monotremes are the only mammals that lay eggs!
- The Marsupials mostly live in Australia, but some live in South America. Baby marsupials cannot survive unless they quickly hide inside their mother’s pouch. There are several orders of marsupial
- The Opossoms of South America, called Didelphimorphia, live in trees and eat anything. They have a strong immune system, and can even survive the bite of a rattlesnake! They also have more teeth than any other land mammal.
- The Shrew Opossums, called Paucituberculata, also live in South America. They look like small Opossums.
- The Monito del Monte (which means Little Mountain Monkey) is the only living animal in the order Microbiotheria. It is about the size of a mouse, but with a longer, thicker, more useful tail and a differently-shaped head.
- Dasyuromorphia means “Hairy tail”. This group includes many carnivorous marsupials from Australia, including Quolls, Numbats, the extinct Tasmanian tiger (or Thylacine), and the endangered Tasmanian Devil.
- There are only two species of Notoryctemorphia, or Marsupial Mole. They are very hard to tell apart. Their pouches face backwards, so they don’t get filled with sand as they burrow through the desert dunes of Australia.
- The Bilby and the 19 types of Bandicoot belong to a group called Peramelemorphia.
- The Diprotodontia contains all the most famous marsupials – the kangaroos and koalas, as well as the wallabies, possums and wombats. They get their name from the Greek words for “two front teeth”. The world’s biggest marsupial, the Red Kangaroo, is in this order.
- There are also two extinct groups of marsupial, one whose members looked like a sabre-toothed cat, and another with boomerang-shaped teeth!
- Most mammals are placental mammals (Eutheria). There are 21 orders of placental mammals.
- The Afrosoricida (from a mix of Latin and Greek meaning “Looks like an African shrew”!) include the tenrecs and golden moles – insect eating animals that live in southern Africa and Madagascar
- The Macroscelidea, called elephant shrews or sengis, also live in Africa. They get their name from their long nose.
- The Tubulidentata contains just one species, the Aardvark. The scientific name comes from its tubular teeth. It eats ants and termites, and almost nothing else (except a strange sort of melon whose fruits grow underground)!
- The hyraxes (Hyracoidea) are animals that live in the Middle East and Africa that, from a distance, could be mistaken for rabbits. The eat grass and leaves.
- The Proboscidea get their name from the Greek word proboskis for “elephant’s trunk”. The only three proboscidae alive today are the three different types of elephant, including the world’s biggest land animal, the African Bush Elephant . Some other animals that once lived in this group are the Mammoth and the Mastadon.
- The Dugong and the three types of Manatee are the only living members of order Sirenia. Like dolphins and whales, these mammals spend their whole lives in the sea. Unlike dolphins and whales, the Sirenians only eat plants.
- The Armadillos, order Cingulata, are odd-looking mammals that love digging. They live in the Americas, as far north as Texas and Florida. Scientists say that one day the Armadillos will even reach Ohio.
- The anteaters and sloths (order Pilosa) also live in North and South America. The sloths are famous for being very slow-moving!
- The Scandentia are Asian mammals called Treeshrews, although they are not shrews, and not all types live in trees.
- The two species of Colugo (Order Dermoptera, meaning “wings of skin”) are large gliding mammals living in Southeast Asia
- The Primates include the monkeys, apes, and people, as well as lemurs, lorids, galagos and tarsiers. The word Primate comes from the Latin word for “first”, because the scientist who gave the name regarded this group of mammals as the most important (naturally, since he was one!). There are over 400 species of primate.
- About 2 in every 5 species of mammal is a rodent. The Rodents, or Rodentia, include mice, rats, squirrels, chipmunks, gophers, and many other animals like them. They get their name from the Latin word rodere, meaning “to gnaw”. Their two front teeth never stop growing! Note that rabbits are not rodents.
- The rabbits and hares (and the pika) belong to the order Lagomorpha. These are similar to rodents, except they have more upper incisors, and almost exclusively eat plants. Lagomorpha comes from the Greek words meaning “shaped like a hare”.
- The 24 types of hedgehog and gymnure (or moonrat) come under an order called Erinaceomorpha. These are reasonably large creatures, with a longish nose, and a short tail. The hedgehog has spines on its back instead of normal hair.
- The shrews, moles, and solenodons live in the order Soricomorpha. The Greek word Sorico just means “shrew”, so these are the “shrew-shaped” mammals. They live in almost every continent in the world, many eating insects.
- The 1100 species of bat, belong to order Chiroptera. This name comes from the Greek for “hand wing”, because their wings are made of skin stretched across their ‘finger’ bones. Most types of bats eat insects, helping people fight against pests that spread disease and attack crops.
- The Pholidota, called Pangolins or Scaly Anteaters, live in the tropics in Asia and Africa. They eat insects, especially ants and termites.
- The Cetaceans (Order Cetacea) include the whales, dolphins, and porpoises – including the world’s biggest mammal, and biggest animal of all time, the Blue Whale. Like the Dugongs and Manatees of order Sirenia, they spend all their lives in the water.
- Order Carnivora includes cats, lions, tigers, dogs, badgers, bears, weasels, seals, lions and many other meat-eating mammals. The word Carnivora comes from the Latin words meaning “meat eater”. Note, however, that some Carnivora are not carnivores – for example, the Panda Bear eats mostly bamboo.
- Horses belong to the order Perissodactyla. So does the zebra, the rhinoceros, the tapir, and so forth. These mostly eat plants, and digest it in their intestines. They have an odd number of toes on each foot.
- Artiodactyla is the name given to the order containing pigs, cows, camels, deer, hippopotamuses and so forth – including the tallest of all living land animals, the Giraffe . They also mostly eat plants. Those that do so have rather complicated digestive systems. They have an even number of toes on each foot.