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)” (1). 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. Before the Young placental mammals are born they spend relatively long time inside their mothers body. They are warmed and protected within the mothers womb; the unborn young are nourished by a soft organ called the placenta. This placenta plays a vital role in absorbing nutrients from the mothers blood and transfers them to the developing young in the bodies. By the time a young placental mammal is born it is usually fully formed, but their eyes are not opened and their teeth not fully formed.

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. “On land, mammals live in many different habitats, and at a wide range of altitudes. Many mammals dig burrows as refuges or as places to raise their young, but some have developed a largely subterranean lifestyle, feeding on small animals or plant roots beneath the soil surface” (2). These placental mammals, “including moles and mole-rats, dig through the ground either with spadelike front paws or with their teeth, and they detect danger by being highly sensitive to vibrations transmitted through the soil” (2).

“Some mammals, such as otters and river dolphins, have adapted to life in freshwater habitats, but the great majority of the worlds aquatic mammals live in the ocean. Seals remain close to coasts or to floating ice, but whales and dolphins are truly pelagic, meaning that they wander far out into open water. Most of these marine mammals live in areas where food is abundant, but where water temperatures are low” (2). “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. By contrast, whales and dolphins have very sparse hair, and keep warm with a thick layer of fat called blubber” (2).

Other placental mammals such as the bats inhabited the skies. The limbs which they were characterised of evolved into wings. By developing these wings enable them to fly. They survive by catching their prey on air. They 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” (2)

The placental mammals that live on land mostly have four legs, which they use for walking on search for food. For example, “the jaguar, a terrestrial carnivore with explosive running power, is adapted for speed on land and this carnivore colonise the land since it is a carnivore, most of its prey lived on land” (2).

Reference:

1. WGBH education foundation, convergence, marsupials and placental, 2001 [Internet] [cited 2006 May 24] Available:
http://www.pbs.org/wgbh/evolution/library/01/4/pdf/l_014_02.pdf

2. “Mammal,” Microsoft®, Encarta® Online, Encyclopedia 2006 [Internet] [Cited 2006 May 24] Available:
http://encarta.msn.com/encyclopedia_761561349/Mammal.html

Mr Lufuno Mukwevho
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