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Monotremes
Monotremes are probably the oldest,living group of mammals.
Like all mammals,they have fur and feed their young on milk but ,unlike other mammals,they do not have nipples.
lnstead,babies suck or lick up the milk from their mother's belly.
The other strange thing about monotremes is that they lay eggs and incubate them.
They are the platypus,which lives only in Australia, and two different kinds of echidna, which live only in Australia and New Guinea.
Marsupials
Marsupials begin life, like most mammals inside their mother where they get their food from the mother's placenta.
However,marsupials are born after a very short time and are quite undeveloped.
Nearly all marsupials have a pouch.
As soon as the baby isborn ，it makes its way into its mother's pouch where it attaches itself to a nipple .
lt stays in this warm pouch,drinking its mothers milk, until it has developed enough keep itself warm and go out into the wide w