Mammals are taxonomically divided into three groups: placentals,
marsupials and monotremes.
The lattest belong to
the smallest group – it contains only three species: the duck billed
platypus and short beaked echidna found in Australia, and long beaked
echidna found in
Platypus. Poster by AllPosters. Click on thumbnail to buy
More Primitive than Marsupials and Placentals
They have never been as numerous as other groups of Australian animals
such as marsupials
Fossil evidence suggests that they were around before the final
break-up of Gondwanaland.
smaller brains than placentals and
marsupials, but like marsupials, their lower metabolic rate and body
temperature make them more energy efficient than placentals.
Echidna. Poster by AllPosters. Click on thumbnail to buy
Both Mammalian and Reptilian Characteristics
Monotremes are the most unique group of Australian animals,
and it took a little bit of confusion before they were classified as
mammals. They do have fur and they produce milk – two most important
features of mammals. But they lay eggs like reptiles, and they have no
nipples - the baby sucks the milk off the fur instead. And like
they have a single hole for eggs, urine and faeces. This mixture of
mammalian and reptilian characteristics suggests that they descended
from a very early branch of mammals.
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