The oldest types of animals in Australia are the ornithorhynchus and the
echidna, the 'beast with a bill,' and the 'porcupine ant-eater' of
popular natural history. These curious creatures, genuine living
fossils, occupy in some respects an intermediate place between the
mammals on the one hand and the birds and lizards on the other. The
echidna has no teeth, and a very bird-like skull and body; the
ornithorhynchus has a bill like a duck's, webbed feet, and a great many
quaint anatomical peculiarities which closely ally it to the birds and
reptiles. Both, in fact, are early arrested stages in the development of
mammals from the old common vertebrate ancestor; and they could only
have struggled on to our own day in a continent free from the severe
competition of the higher types which have since been evolved in Europe
and Asia. Even in Australia itself the ornithorhynchus and echidna have
had to put up perforce with the lower places in the hierarchy of nature.
The first is a burrowing and aquatic creature, specialised in a thousand
minute ways for his amphibious life and queer subterranean habits; the
second is a spiny hedgehog-like nocturnal prowler, who buries himself in
the earth during the day, and lives by night on insects which he licks
up greedily with his long ribbon-like tongue. Apart from the
specialisations brought about by their necessary adaptation to a
particular niche in the economy of life, these two quaint and very
ancient animals probably preserve for us in their general structure the
features of an extremely early descendant of the common ancestor from
whom mammals, birds, and reptiles alike are originally derived.
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