There are approximately 4500 species of mammals. Despite the fact they represent a very small fraction of the world’s animals, mammals are among the world’s best known species.
New species of mammal are still being discovered although many more go extinct than are discovered.
Subclasses of Mammals
This is an extremely small subclass that is composed of 5 species belonging to the order Monotrema. These are the egg-laying mammals.
There is the duck-billed platypus and four species of echidna. All five species are found in Australia and New Guinea.
These are the marsupials. They give birth to immature young that live in the mother’s pouch until they are able to emerge into the world.
This subclass is divided into seven orders and includes species like:
Many, though not all, of these species live in Australia and South America.
This is the largest subclass of mammals. It includes most of the mammals that people are familiar with including:
carnivora (cats, bears, pinnipeds, canines)
cetacean (marine mammals including whales and dolphins)
lagomorpha (rabbits, hares, pikas)
sirenia (sea cows, manatees)
proboscidea (elephants, mammoths, mastodonts)
artiodactyla (even-toed ungulates including sheep, cows, pigs, deer, and antelope)
perissodactyla (odd-toed ungulates such as horses, tapirs, rhinos).
Mammals are found in all types of environments. A mammalogist can research everything from genetic and cellular level interactions to ethology and ecology of an animal species or community.
Mammals are favourites for studies on learning and communication, particularly in cetaceans, proboscidea and primates. The unique aspects of monotremes and marsupials makes them particularly interesting to those that are looking at the evolution of mammals and how the breakup of Pangaea affected evolution.
Monotremes are believed to have split from the main line of mammals approximately 190 million years ago and marsupials are believed to have split off about 100 millions years ago.
Many mammals are considered endangered; particularly rhinos, some primates, and many of the big cats. Habitat destruction and poaching have had a profound impact on many species rich environments.
Because many mammals are K selected species, they cannot replenish their population very quickly. There is also a loss of genetic diversity after a species reaches a certain number of individuals that makes it very vulnerable to disease.
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