The class Mammalia includes about 5000 species placed in 26 orders. Systematics do not agree on the exact number or on how some orders and families are related to others.
The animal diversity generally follows the arrangement used by Wilson and reader. The dependence of the young mammal on its mother for nourishment has made possible a period of training. Such training permits the non-genetic transfer of information between generations. The ability of young mammals to learn from the experience of their elders has allowed a behavioral plasticity unknown in any other group of organisms and has been a primary reason for the evolutionary success of mammals.
All mammals share at least three characteristics not found in other animals they are three middle ear bones, hair and the production of milk by modified sweat glands called mammary glands. Hair has several functions including insulation color patterning and aiding in sense of touch. All female mammals produce milk from their mammary glands in order to nourish newborn offspring. Thus female mammals invest a great deal of energy caring for each other offspring which has important role in their offspring.
Last date updated on September, 2014