Mammals
do not have scales, they generally have hair. Some mammals have
more hair than others. Cetaceasn generally don't have hair.
Some have bristles on the head called "vibrissae"
(a little bit like the whiskers on a cat!!).
Most
mammals have hair to keep them warm (think of the polar bear!).
Cetaceans have a thick layer of fat just under the skin (called
blubber) which keeps them warm instead. Having no hair means
the cetaceans are more streamlined and can more through the
water easily.
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