Mammals

Mammals are a class of animals belonging to the Phylum Chordata and Subphylum Vertebrata. They are defined by certain characteristics which all mammals share, including: glands that produce milk, hair, three bones in the middle ear, and a neocortex in the brain.

Most mammals are born live, but there are exceptions. Monotremes, including the echidna and the platypus, lay eggs. Most other mammals give birth to live young mature enough to live outside the womb (called placental mammals). Some are born under developed and live for a while in a special pouch until mature enough to enter the world (called marsupials).

There may be some confusion about mammals which do not appear to have hair, such as porpoises. ALL mammals do have hair, at least at some point in their lives. For some it is just a few whiskers or ear hair which may even fall out by the time the animal reaches maturity. A mammal is a animal that is warmblooded vertebrate ( which means a animal with a backbone) It must have at least a little bit of fur (hair) on its body. Also a mammal's baby must be born alive and must drink it's mother's milk.
The official definition for the word mammal is "a warm-blooded vertebrate animal of a class that is distinguished by the possession of hair or fur, the secretion of milk by females for the nourishment of the young, and the birth of live young."

Mammals are warm blooded. They also have hair or fur. They all almost give live birth but a couple of them lay eggs.

Mammals (formally Mammalia) are a class of vertebrate animals whose name is derived from their distinctive feature, mammary glands, with which they feed their young. They are also characterized by the possession of sweat glands, hair, three middle ear bones used in hearing, and a neocortex region in the brain. Except for the three species of monotremes (which lay eggs), all mammals give birth to live young. Most mammals also possess specialized teeth, and the largest group of mammals, the placentals, use a placenta during gestation. The mammalian brain regulates endothermic and circulatory systems, including a four-chambered heart. There are approximately 5,400 species of mammals, ranging in size from the 30-40-millimetre (1.2-1.6 in) Bumblebee Bat to the 33-metre (110 ft) Blue Whale, distributed in about 1,200 genera, 153 families, and 29 orders,[1] though this varies by classification scheme. The mammals are divided into two subclasses, the prototheria, which includes the egg-laying monotremes, and the theria, which includes the live-bearing marsupials and placentals. Most mammals, including the six largest orders, belong to the placental group. The three largest orders, in descending order, are Rodentia (mice, rats, and other small, gnawing mammals), Chiroptera (bats), and Soricomorpha (shrews, moles and solenodons). The next three largest orders include the Carnivora (dogs, cats, weasels, bears, seals, and their relatives), the Cetartiodactyla (including the even-toed hoofed mammals and the whales) and the Primates to which the human species belongs. The relative size of these latter three orders differs according to the classification scheme and definitions used by various authors. Phylogenetically, Mammalia is defined as all descendants of the most recent common ancestor of monotremes (e.g., echidnas and platypuses) and therian mammals (marsupials and placentals).[2] This means that some extinct groups of "mammals" are not members of the crown group Mammalia, even though most of them have all the characteristics that traditionally would have classified them as mammals.[3] These "mammals" are now usually placed in the unranked clade Mammaliaformes. The mammalian line of descent diverged from the reptile line at the end of the Carboniferous period. The majority of reptiles would evolve into modern-day reptiles and birds, while the synapsid branch led to mammals. The first true mammals appeared in the Jurassic period. Modern mammalian orders appeared in the Palaeocene and Eocene epochs of the Palaeogene period.
Lion Tiger People Sea Lion
A mammal is an animal that carries a baby in its pouch

There are over 65 species of kangaroos, and they are herbivores or omnivores because this suits me best in their habitat.

Australia is characterised by vast tracts of bushland, and the animals most commonly known as kangaroos are herbivores, siting this habitats, as they primarily eat grass and other vegetation. Besides grass, they eat young shoots and tender leaves of native shrubs. Kangaroos are grazing animals, and they will regurgitate their food to chew like cattle chew their cud. These kangaroos include the larger red and grey kangaroos, as well as wallaroos, wallabies, quokkas, potoroos and bettongs/rat-kangaroos. Bettongs also eat fungi and tubers, because these are found in their habitat. Smaller varieties of kangaroos such as the musky-rat kangaroo are omnivores, eating fruits, seeds, fungi insect larvae and small invertebrates such as grasshoppers and beetles, as these foods are abundant on the rainforest floor where this particular species of kangaroo lives.

Tree kangaroos, which live in rainforests of far North Queensland as well as the island of New Guinea, eat leaves, and sometimes fruit. Some varieties of tree kangaroo are omnivores, eating insects and other invertebrates. The Goodfellow's tree kangaroo has been known to eat eggs and small birds as well. These foods are abundant in their habitat.

All mammals are covered in either hair/fur.

Answer Improved by: -k-
Mammals would be covered with hair. Mammals are warm blooded and grow hair on their bodies. Other non-mammal species might grow fur, feathers, or another type of body covering but its not the same as hair.

Birds and mammals both have the following:

• a backbone and internal skeleton, as they are vertebrates
• they are warm-blooded
• they breathe using lungs (not gills)

The largest water mammal is Blue Killer Whale.

Additional answer

Actually, the blue whale and the killer whale are two different animals, with the blue whale being much the bigger.