Types of Mammals
Monotremes: The monotremes are primitive egg-laying mammals. Modern-day monotremes include the echidnas (spiny ant-eaters) and the duck-billed platypus.

Marsupials: Marsupials are another group of mammals; their young are born in an extremely immature state; most female marsupials have pouches. Some marsupials include the koala, kangaroo, and the numbat.

Placental mammals: Placental mammals are mammals whose young are born at a relatively advanced stage (more advanced than the young of other mammals, the monotremes and marsupials). Before birth, the young are nourished through a placenta. The placenta is a specialized embryonic organ that is attached the mother's uterus and delivers oxygen and nutrients to the young. Most mammals are placental mammals, like cats, dogs, horses, and people.

Diet
Mammals have to eat a lot to maintain their high body temperature. Diets vary from genus to genus. As with most animal groups, there are more herbivores (plant-eaters) than there are carnivores (meat-eaters).

Types of Mammalian Diets:

• Herbivores (plant eaters) - including beavers, cows, horses, pandas, sloths, and others
• Carnivores (meat eaters) - including whales and dolphins, dogs, tigers, lions, and others
• Omnivores (eat plants and meat) - people, some bears, and others
• Insectivores (eat insects) - aardvarks, anteaters, pangolins, and others

Mammal Extremes

• Fastest mammal (also the fastest land animal): the cheetah (60-70 mph = 97-110 kph)
• Slowest mammal - the sloth (less than 1 mph, or 2 kph)
• Biggest mammal, biggest animal that ever lived on Earth - the blue whale
• Biggest land mammal- the African Elephant
• Tallest mammal - the giraffe
• Smallest mammals - the pygmy shrew (weighing 1.2-2.7 gm) and the bumblebee bat (weighing about 2 gm)
• Loudest mammal - the Blue Whale. The second loudest is the Howler Monkey.
• Smallest newborns - marsupials (pouched mammals, like the kangaroo)
• Smelliest mammal - the striped skunk (Mephitis mephitis)
• The only venomous mammals - duckbilled platypus (males only), several species of shrews, and the Solenodon
• Fat - The blue whale has the thickest layer of blubber, but ringed seal pups have the greatest percentage of fat (about 50 %).