What is a platypus?

Platypuses are monotremes, a rare group of egg-laying mammals that also includes echidnas. They have webbed feet, dense waterproof fur, and a sensitive bill used to detect electrical signals from prey underwater. Males have a venomous spur on the hind leg, one of the few venomous mammals known. When first described by European scientists in the late 18th century, the platypus was so unusual that some thought it was a hoax.