Page 9 - Mammal (DK Eyewitness)

homoiothermic, meaning that a constant internal body temperature is maintained, usually
above that of the environment, rather than adjusting to the temperature of the surroundings.
In this way mammals can stay active even in cold conditions. Three, mammals feed their
young on milk. The milk is made in specialized skin structures called mammary glands; hence
our group’s biological name, Mammalia. This book sets out to explore the world of the
mammals - what they look like, their body structure,
evolution, breeding habits, and behavior - and in
doing so will hopefully cast some light on
our place in this group.

MAMMALS AS ANIMALS
There are about 4,000 species (types) of mammals.
Because of the number of domestic species, and the
popularity of mammals in zoos, we are more familiar
with them than other animal groups. Yet there are
some 9,000 species of birds, 20,000 species of fish,
and 100,000 species of spiders and scorpions. All
these pale against the greatest animal group - the
insects, with at least one million species, and
possibly 10 times that number.

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