The Australian short-beaked echidna, a monotreme, is one of the oldest living mammals on earth.

澳大利亚短吻针鼹，一单孔类动物，是现存最古老的地球上的哺乳动物之一。

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The long-beaked echidna is an endangered animal that only lives north of Australia, on New Guinea and nearby islands.

VOA: special.2009.07.07

Some may be taxonomically unique the last representative of an otherwise extinct group of animals, like the duck-billed platypus or the long-beaked echidna while others may differ from each other only slightly.

ECONOMIST: Green.view: Finger on the spot | The