The rise of the mammals

The emergence of tropical rainforests, of temperate woodlands, of savannah and prairie grasslands, all provided new habitats for mammals to exploit. Mammals have inhabited all continents, most large islands and the oceans worldwide. Today, Antarctica is the only large landmass without resident mammals, save for the sealions that frequent its shores. However, back in Eocene times, some 50 million years ago, Antarctica had a wooded landscape in which lived marsupial mammals.

Mammals enjoyed their maximum diversity about 15 million years ago, during the Miocene. Since then, world climates have deteriorated, culminating in the Great Ice Ages of the Pleistocene, which began about 2 million years ago. Animal diversity is always greatest in the tropics, and the shrinkage of tropical habitats is largely responsible for the decline in the total number of mammal species. The alternating cold and warm periods of the Ice Age did, however, encourage the evolution of many remarkable large mammals, such as the wooly mammoth, giant deer and ground sloths — all of which have disappeared within the last 12,000 years.

An active lifestyle calls for a high degree of control over the nervous system, so mammals have a large and complex brain capable of rapidly processing information fed to it from the eyes, nose and ears.

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