Echidnas are monotremes (egg-laying mammals) that are native to Australia and New Guinea. Echidnas can give the platypus a run for its money in the category of weirdest mammal. The list of features that make this animal unique is a long one.
Like their platypus relatives, echidnas can be described as an amalgam of familiar and unique features. They have a toothless, pointy snout like a cross between a bird and an anteater. They lay eggs like a reptile, have thick spines like a porcupine and a pouch like a marsupial. Their front feet resemble spades and their hind feet point backwards. They walk like no other creature on Earth, as if at the behest of someone who is learning how to operate a remote-controlled robot, stopping and starting and changing direction every couple of steps. The way their limbs move, held at 90 degrees from the body, is unique. In every respect, echidnas are delightful.
But that's just the beginning! Echidnas have several weird responses to danger, including suddenly burying themselves with only their spines protruding above ground. They can also sense electricity, which is probably left over from their ancient ancestors that lived in water. Oh yeah, there's more that makes the echidna unique among animals, that you can read about at Atlas Obscura.
(Image credit: paweesit)