Animals / Mammals

Mammals

There are about 5,400 species of mammals in the air and water and on the land.

Some of the orders of mammals are:

Monotremata (egg-laying marsupials)
Marsupialia (marsupials)
Insectivora (insectivores)
Chiroptera (bats)
Dermoptera (flying lemurs)
Macroscelidea (elephant shrews)
Scandentia (tree shrews)
Primates (primates)
Xenarthra (anteaters and relatives)
Pholidota (pangolins)
Lagomorpha (rabbits, hares, and pikas)
Rodentia (rodents)
Cetacea (cetaceans)
Carnivora (carnivores)
Pinnipedea (seals and sea lions)
Proboscidea (elephants)
Tubulidentata (aardvark)
Hyracoidea (hydraxes)
Sirenia (dugongs and manatees)
Perissodactyla (odd-toed hoofed mammals)
Artiodactyla (even-toed hoofed mammals)

Some characteristics of mammals are:

mammary glands
hair
diaphragm
three middle-ear ossicles
heterodont dentation
sweat, sebaceous, and scent glands
four-chambered heart
large cerebral cortex

Mammal record setters - the big, the bad, and the ugly:

Fastest - cheetah at 60-70 mph (97-110 kph)
Slowest - sloths
Biggest - blue whale
Biggest on the land - african elephant
Biggest primate - gorilla
Biggest fish - whale shark
Tallest - giraffe
Smallest - pygmy shrew (1.2-2.7 g) or maybe the bumblebee bat (about 2 g)
Loudest - blue whale
Loudest on land - howler monkey
Smelliest - striped skunk
Ugliest - aye-aye or maybe the solenodon
Fatest - blue whale
Badest - man
Wickedest - bats
Venomest - male duckbilled platypus, some shrews, and the solenodon

Wikipedia excerpt for "Mammal":

Mammals 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 3 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.
The mammals are divided into two subclasses. Most mammals, including the 6 largest orders, belong to the placental group. The 3 largest orders, in descending order, are Rodentia (mice, rats, and other small, gnawing mammals), Chiroptera (bats), and Soricomorpha (shrews, moles and solenodons). The next 3 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 (that's us!).

See full Wikipedia Mammal article