Thursday, April 26, 2012

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.