2011年8月17日星期三

What is a Mammal?

What is a Mammal?

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A mammal is a class of animals that comprises the biggest species on earth, including humans. There are 5,400 mammal 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: Mammary glands. A mammal can produce milk to feed its young, as opposed to other species, which feed their offspring with solid food. A mammal young is born alive, except for a few species, such as the monotremes family, which lay eggs. Warm blood. A mammal has warm blood, which helps the animal maintain steady body temperature. A mammal also has a heart with four chambers, a unique characteristic that allows the lungs to receive oxygenated blood in proper amounts. Mammal bodies are all covered with some kind of hair or fur that helps with heat preservation. 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. A mammal has 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. A mammal has a larger percentage of fat deposits than any other animal class; this helps mammals with energy storage and thermal insulation. A mammal can survive a longer time without food or water than any other species on earth.

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