Long-beaked echidna are monotremes, or egg-laying mammals. The creatures are critically endangered and are thought to live only in the New Guinea rainforest.
Monotremes like the duckbill platypus lay eggs like reptiles but give milk to their babies like all other mammals. The primitive lineage may have diverged from all other mammals around 220 million years ago.
Unlike their longer-beaked cousins, short-beaked echidnas are still frequently seen in Australia.
Long-beaked echidnas are nocturnal and secretive, making them hard to spot in the wild. Here, zoologist Kristofer Helgen holds the long-beaked echidna in Papua New Guinea.
Fossils and aboriginal rock art revealed that the long-beaked echidna once lived in Australia, though experts thought it had disappeared from Australia between 30,000 and 40,000 years ago.
But in 1901, naturalist John Tunney led an expedition across Australia and shot a long-beaked echidna in Western Australia. The specimen was transferred to the Natural History Museum in London.
The specimen was stuffed in a drawer at the museum and forgotten for a century, when zoologist Kristofer Helgen discovered it by chance.
The specimen was neatly tagged with where and when it was taken. It was even marked as rare.
The specimen shows that long-beaked echidnas lived in Australia as recently as a century ago, and aboriginal reports suggest it still lived even more recently.That raises the possibility that the elusive creatures may still exist somewhere in Australia.