Why does the platypus have melanin structures similar to birds? No one really knows.

They already have the bill of a duck, the tail of a beaver, lay eggs like reptiles and have venom like snakes.

Yet the humble platypus, a small creature which quietly swims in the rivers of eastern Australia, has found yet another way to amaze scientists.

It is the only mammal that has hollow structures of the pigment melanin, a trait normally found in birds, biologists said in a new study on Wednesday.

When the first taxidermied specimen of a platypus was brought back from Australia in 1799, European naturalists began looking for the seams—they assumed it was a hoax.

The animal has been surprising scientists ever since.

The platypus is one of only five mammal species that lay eggs, which are called monotremes .…