MAMMALS -I-
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MAMMALS -I-
The most highly-developed animal group. Origins. Characteristics.
Different types of teeth.
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INTRODUCTION
Mammals’ main characteristics.
There are more than a million species of insects, 20,000 kinds of fish, 8,500 different birds, but there are only 2,500 species of mammals.
Mammals have some common characteristics which help to explain their successful evolution.
ORIGIN OF MAMMALS
Around 200 million years ago some small, five fingered, insect eating mammals made their appearance.
When great reptiles disappeared were replaced by mammals.
Changes in the Earth’s climate favoured the evolution of mammals.
The Austrolopithecus.
The Ice Ages. The woolly rhinoceros and the mammoth.
Predators found in the warmer regions. The sabre-tooth tiger.
GENERAL CHARACTERISTICS
Many mammals have fur covering their skin to conserve their internal warmth.
Birds and mammals have an automatic system controlling their internal temperature.
Control of temperature, contraction and dilation of blood vessels, sweat glands start or stop functioning, hair becomes erect, thereby creating an isulating layer.
These controls governing their internal temperature are coordinated by the brain.
Development of different kinds of teeth which vary according to their function. Wolves, deers, porcupines.
Whales have no teeth, but huge filters.
The actual number of new-born varies between different species.
SUMMARY |
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