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A mammal is member of the Mammalia class of animals, and includes many familiar creatures, including humans. There are more than 5,000 species, most of which live on land, excluding a few species such as dolphins, whales, and manatees. A mammal can be recognized by a series of unique characteristics, which include the following:
- Mammary glands. A mammal can produce milk to feed its young, as opposed to other species, which feed their offspring with solid food. Young are born alive, except for a few species, such as species in the monotremes order, which lay eggs.
- Warm blood. Animals in this class have warm blood, which helps them maintain steady body temperature. They also have a heart with four chambers, a unique characteristic that allows the lungs to receive oxygenated blood in proper amounts. These animals have bodies that are all covered with some kind of hair or fur that helps with heat preservation, and even aquatic mammals have hair at some point during their life.
- Neocortex. A mammal posses a brain section that does not occur in any other animal class. The neocortex is the section that controls language, motor commands, and conscious thought. While birds and certain reptiles seem capable of experiencing some of these characteristics, the neocortex is still unique to mammals.
- Size. Mammals have the largest difference between the smallest (bats) and the largest (blue whale) species: a 53 million-fold. No other animals come even close in comparison.
- Skeleton. Animals in this class have fewer bones than other animal classes; they also have a rigid rib cage, solid hip attachments, specialized adapted teeth, simplified limbs, and increased size of the brain case.
- Adipose tissue. Mammals have a larger percentage of fat deposits than any other animal class; this helps them with energy storage and thermal insulation. A mammal can survive a longer time without food or water than any other species on Earth.