Types of Mammals

In terms of reproductive behavior, mammals fall into three groups- the egg layers, the pouched mammals and the placentals. The egg layers or monotremes, show several reptilian features and are represented only by the platypus and the echidnas. The pouched mammals, or marsupials, are confined mainly to Australia and New Guinea. They are born at very early stage – the new born red kangaroo is about the size of a broad bean- and continue their development while feeding on milk in a pouch on the mother’s body. Placentals, which make up the vast majority of living mammals, give birth to their young at a much later stage of development. While inside the mother’s body the offspring are nourished by the placenta, through which food and oxygen pass from the mother’s blood stream to the foetal blood stream. Many placental babies are so well developed by the time of birth that they can run about almost as soon as they are born.

Man has domesticated many mammal species for both work and pleasure, and has also created many different new breeds. Small mammals, especially rodents such as mice, gerbils, hamsters and guinea pigs, make excellent pets for children. Among slightly larger animals, cats and rabbits make good pets. Dogs were the first animals to be domesticated, probably over 10,000 years. Their ancestors were almost certainly a race of small wolves that lived in Southwest Asia. There are now well over 400 recognized breeds of dogs, including a wide range of working and sporting dogs as well as the more familiar pets.

Horses were first domesticated more than 4,000 years ago, when at least two breeds of wild horses- the Tarpan and Prexewalski’s horse – roamed the steppes of central Asia. One or both of these may have contributed to the domestic horse. Many breeds of horse now exist, from tiny ponies to the great shire horses once common farm animals and now making a comeback as draught animals.

Mammals

       Mammals are generally considered to be the most advanced group of animals; this is the class that contains man and the ape. All mammals have relatively large brains and a greater capacity for learning than most other animals. Unlike that of a reptile, the lower jaw of a mammal consists of a single bone, the dentary, on each side. This of great help to paleontologists in identifying fossil skeletons. Mammals first appeared on the earth a little over 200 million years ago, the descendants of some small insect eating reptiles, but they did not come to prominence until the extinction of the dinosaurs about 65 million years ago.

        When the dinosaurs disappeared, mammals were able to investigate many different ways of life and evolve in different directions. Since then thousands of species have come and gone many of them weird experimental forms such as the shovel lipped elephant and the giant Baluchitherium. The latter looked like a cross between a rhinoceros and a giraffe and, with a weight of perhaps 30 tones, was the largest of all known land mammals. Today, however, there are only about 4,100 mammalian species. The mammal teeth vary according to the animal’s diet. Carnivores have sharp edged cheek teeth that are suitable for slicing through meat. Herbivores, in contrast, have flat grinding teeth. Rodents have chisel like front teeth.