Vol 3 Mammals of Africa ... Introduction ... Evolution of mammals
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Introduction

Evolution of mammals

Relatives of the camel, elephants and lions used to live in North America!
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Mammals first appeared in the Cretaceous period, some 100 million years ago. They probably evolved from the cynodonts, a group of 'mammal-like reptiles', that appeared before the age of the dinosaurs. The first mammals were small, shrew-like creatures that may have survived because they were small and nocturnal, foraging for insects while the dinosaurs were inactive.

There is much debate about the end of the dinosaurs and the rise of the mammals. One theory that should be discarded is that the small mammals ate the dinosaur's eggs! This is just too simplistic to be true, because if it had any validity there would be no egg-laying reptiles in the world today. The true reason for the demise of the dinosaurs may have been related to a change in climate around 65 million years ago.

The main groups of large animals that survived the dinosaurs were the mammals and the birds. Both of these groups are warm-blooded, both have skin insulated by feathers, hairs or thick fat deposits, and both nuture their young. A combination of these factors may have enabled birds and mammals to weather any climatic change that killed the dinosaurs.

The presence of hair and associated skin glands gives mammals several advantages over other surviving groups, such as the reptiles. They are insulated against heat and cold, and skin secretions may waterproof the skin and help temperature regulation.

Mammals are also aided by not having to protect externally-laid eggs, increasing the chances of survival. They also have limbs that are well placed for quick movement (reptile and amphibian limbs for example jutt out from the body and are often clumsier).

The distribution of mammals that we see in the world today is very different from the distribution that existed millions of years ago, and many African mammals lived far from Africa. Relatives of the camels, elephants and lions used to live in North America, and aardvarks and rhinos were found in Europe. You'll find out more about the distribution of African mammals in the past as you read the sections on the different mammals in this web site.