Parma Wallaby (Macropus parma)
A wallaby is any of about thirty species of macropod (Family Macropodidae). It is an informal designation generally used for any macropod that is smaller than a kangaroo or wallaroo that has not been given some other name. Very small forest-dwelling wallabys are known as pademelons and dorcopsisis. The name wallaby comes from the Eora Aboriginal tribe who were the original inhabitants of the Sydney area. Young wallabys are known as "joeys", like many other marsupials.
Wallabys are widely distributed across Australia, particularly in more remote, heavily timbered, or rugged areas, less so on the great semi-arid plains that are better suited to the larger, leaner, and more fleet-footed kangaroos. They also can be found at the island of New Guinea.
Wallabys are not a distinct biological group. Nevertheless they fall into several broad categories. Typical wallabys of the Macropus genus, like the Agile Wallaby (Macropus agilis), and the Red-necked Wallaby (Macropus rufogriseus) are most closely related to the kangaroos and wallaroos and, size aside, look very similar. These are the ones most frequently seen, particularly in the southern states.
Source: en.wikipedia.org/wiki/Wallaby - 30.06.2011
Kangaroo - Weight at Birth less than 1 Gram
After conception the embryo of a kangaroo develops under completely different circumstances than those of most of the other mammals.
Already after a short gestation period of 20 to 40 days the joey (the young one) is born, still completely depauperate and without looking like a kangaroo. With the biggest species of kangaroos, the red kangaroo (Macropus rufus), the chick weighs at birth 0,75 grams, measures 2,5 centimetres and looks like a red worm.
Now something happens that is nearly inconceivably: After birth the tiny one crawls by itself (using only its own power) from the birth canal into the sac of the mother, clings with its mouth on a teat and does not let go of it during the next two to three months.
It lasts circa six months till the joey, now looking like a kangaroo, leaves the sac for the first time. Two month later it does no longer fit in its nursery, but it continues to be nursed until it reaches the age of one year. Therefore it only has to put its head in its mother's sac, where often a new baby is already being fed. The mother has different teats, so that the older kangaroo joey can not take away the food from the smaller one. Moreover these teats produce milk of different consistency.