HOW PLACENTA MAMMALS HAVE COLONIZED LAND, WATER AND AIR

The placental mammals are very diverse species and range from elephants, whales, shrews, and armadillos. They also include pets such as dogs and cats, as well as many other animals such as sheep, cattle, and horses. It is also recognised that human being are also the placental mammals. They form a very diverse group of species and their young’s are born at relatively advanced stage as compared to other mammals.


The placentals mammals include about 4300 species, making it by far the largest of all three mammal groups. Young placental mammals spend a relatively long time developing inside the body of their mother before birth. They are protected within the womb, which is nourished by a spongy organ called the placenta. This serves to absorb nutrients from the blood of the mother and transfers them to the developing animal. By the time a young placental mammal is born, it is usually fully developed, although it may not yet have fur, functioning eyes or teeth.


Some placental mammals have adapted to survive in the water, land and air. They have developed different body shapes and sizes, which act as the driving forces behind colonising water, land or air. They have wings to survive in air, feet to survive in land and gills to survive in the water. Species such as Seal, sea lions and walruses as for example, have adapted to live in both land and in the water. These species do sleep and feed in the ocean but they return to land in order to reproduce. However, manatees and dugongs are large, plant-eating mammals that spend their entire lives in the water.


In the same manner, whales and dolphins are well adapted as fast, open-ocean predators. Most aquatic animals still need to breathe because they can drown, but whales and dolphins are truly pelagic, meaning that they wander far out into open water. These marine placentals mammals colonize areas where food is abundant and where the water temperatures is low. They survive the cold temperature in two different ways; firstly -Others such as sea otters and fur seals have a double coat of fur, with extremely dense under fur hairs that are so closely packed that the skin never gets wet. Secondly -whales have very sparse hair, and keep warm with a thick layer of fat called blubber. Such characteristics enable this species to survive even in low temperature.


In addition, dolphins have adapted for an aquatic lifestyle, by having flippers that help them glide through the water. The manatees and dugongs are large, plant-eating mammals that spend their entire lives in the water. Contrary, the jaguar, a terrestrial carnivore has explosive running power, which enables them to survive on land. This species colonise the land and most of its prey lived on land. Other species such as bat have evolved limbs into wings that enable them to inhabit the skies. Generally, mammals have adapted to some of the most extreme habitats on earth. They are warm-blooded, or endothermic, meaning that they maintain their body temperature within a narrow range despite changes in the environment.

Reference


1. Wikipedia contributors, Whales [Internet] The Free Encyclopedia, [ Cited 2006 May 12]
Available From:
http://encarta.msn.com/encyclopedia_761565254_2/Whale.html

2. Mammal, [Internet] [Cited 2006 May 12] Available From:
http://encarta.msn.com/encyclopedia_761561349/Mammal.html


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