DESCRIBE HOW PLACENTAL MAMMALS HAVE COLONIZED LAND, WATER AND AIR

Placental mammals are diverse group whose young are born at relatively advanced stage (more advanced than the young of other mammals). The placental mammals include such diverse forms as elephants, whales, shrews, and armadillos. They include pets such as dogs and cats, as well as many farm and work animals, such as sheep, cattle, and horses. A human falls under the placental mammals.

The placentals mammals are by far the largest of all three mammal groups. Young placental mammals spend a relatively long time developing inside their mother’s body before birth. Warm and protected within the mother’s womb, the unborn young are nourished by a spongy organ called the placenta, which absorbs nutrients from the mother's blood and transfers them to the developing animal. By the time a young placental mammal is born it is usually fully formed, although it may not yet have fur or functioning eyes or teeth.

Some placental mammals have adapted to life and colonise water, land and air. Placental Mammals have developed different body shapes and sizes. These body size and shape were the other driving forces behind colonising water, land and air. Some are able to fly (with wings), those with four limbs to walk, bipedal and those with gills. Instead, most aquatic mammals eat animal as food, but they catch it in two quite different ways. Pursuit hunters, such as otters, seals, and toothed whales, chase individual prey through the water, much like carnivores chase their prey on land. However, the largest whales feed on much smaller animals, scooping them up in vast quantities. These whales do not have teeth, and instead strain their food with a screen of fibrous plates called baleen.

The whales, including the huge baleen whales and the dolphins, are well adapted as fast, open-ocean predators. The aquatic placental mammals 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, but where water temperatures are low. They survive the cold in two different ways. Some, such as sea otters and fur seals have a double coat of fur, with extremely dense underfur hairs that are so closely packed that the skin never gets wet. Whales have very sparse hair, and keep warm with a thick layer of fat called blubber.

The ways in which mammals move from place to place is greatly varied. Some mammals use four limbs to walk (such animals are referred to as quadrapedal) while others use only two (such animals are referred to as bipedal). The greatest differences in locomotion adaptation can be seen when comparing placental mammals from very different habitats. The jaguar, a terrestrial carnivore with explosive running power, is adapted for speed on land. The placental mammals that live on land mostly have four legs, which they use for walking on search for food. This carnivore colonise the land since it is a carnivore, most of its prey lived on land. They are warm-blooded, or endothermic, meaning that they maintain their body temperature within a narrow range despite changes in the environment.

The limbs of bats have evolved into wings enabling them to inhabit the skies and able to catch their prey on air.
The majority of bats also feed on insects, using different technique for catching their flying prey. Using a system called echolocation; a bat sends out bursts of high-pitched sound toward objects and interprets the returning echoes as images that guide a bat toward its prey so that it can hunt even in total darkness





Reference:

1. Mammal, [internet] [cited 2006 may 8]. Available from:
http://encarta.msn.com/encyclopedia_761561349/Mammal.html


Mr Lufuno Mukwevho
CSIR Pretoria
P.O. Box 395
Pretoria,
0001
Tel: (012) 841 2133
Fax: 012 842 7024.
Cell: 0723175626
Email: lmukwevho@csir.co.za
My bloger URL: http://mukwevholufuno.blogspot.com