Mammals

Look around you and you'll more than likely spot one mammal or two. Aside from humans, mammals make up the majority of species on this earth. From the giant anteater to the house mice, our planet is filled with all types of mammals. Mammals are animals that breath air, have a backbone, produce milk, are warm-blooded and covered in hair. Only monotremes, the most primitive mammals, lay eggs (these include the Platypus and the spiny Echidna). All others either develop their young in the womb (Placental Mammals), or a pouch (Marsupials). There are 5,000 species of mammals. If fact, mammals are currently the dominant life form on this planet. These types are divided into three subclasses and roughly 26 orders.http://www.enchantedlearning.com/subjects/mammals/Groups.shtml

The first mammal may never be known. There are two contenders that anthropolgoists believe could be take the crown. The Genus Morganucodon and Morganucodon Watsoni. It is a long, weasel-like animal whose fossils have been found in the following locations: Wales, China, India, North America, South Africa, Western Europe.http://www.earthlife.net/mammals/evolution.html The other mammal is the Gondwanadon Tapani. It was reported to have been found in India when a single tooth was found in 1994. The tooth was dated around 225 MYA.http://www.earthlife.net/mammals/evolution.html

Monotremes are thought to have diverged from other mammals up to 200 million years ago, while Marsupials and Placental Mammals are thought to have split at least 120 million years ago—these figures, however, remain subject to ongoing scientific debate. The vast majority of mammals, ranging from humans (Homo Sapiens) to Narwhals, are Placental, and Marsupials are the second-largest group, with about 334 species.

From Small to Large
The smallest mammal known to man is Kitli's Hog-Nosed Bat. This bat from Thailand is only 2.9 to 3.3 cm and weighs only 1.7 to 2 grams. This bat is smaller than many insects, including snails. The largest mammal is the Blue Whale. A female whale was recorded weighing in at 171,000 kgs and over 90 feet long.http://www.extremescience.com/zoom/index.php/animal-kingdom-records/21-biggest-mammal

The Fastest & Slowest Mammals
The fastest mammal on land is the Cheetah. It reaches speeds up to 60 mph. The Killer Whale takes the gold for the fastest mammal in the water. The whale has been recorded reaching speeds of up to 34 mph. It's a bird, it's a plane, it's the Big Brown Bat. This bat is the fastest mammal in the air with a recorded fligh of 15.5 mph. The sloth is the slowest mammal. It averages of a speed of less than 1 mph.http://www.enchantedlearning.com/subjects/mammals/Mammals.shtml