A mammal with the "weirdest" penises in the animal kingdom has baffled scientists.

The "very strange and unusual" appendage of the echidna remains a mystery to researchers who still don't understand why it has four heads.

The "very long" phallus makes up a third of the animal's body while erect, is bright red and has four endings, which can all be used for the purpose of reproduction.

An echidna is similar to an anteater but has prickly fur. They live in Australia and Papua New Guinea.

University of Queensland researcher Dr Steve Johnston co-authored a study on the peculiar creature's impressive member.But he said only "the creator God" knows why it is so bizarrely shaped.

It may be to please the insatiable female echidna, who scientists believe may mate with up to a dozen males while ovulating.

When the echidna has sex, two of the four prongs are engorged while the others are flaccid.

Experts also speculated that the animals may have Dr Johnston, of the Australian university, said: "It does look like they do it more than once, but there's still a bit of debate. We're not quite sure whether these guys are induced ovulators or not."

The shape and comparative size of the creature's penis is not the only peculiarity about it, researchers say.

Dr Johnston added: "Not only is the (echidna) penis strange in the way it looks, it's also strange in terms of they don't actually urinate through their penis.

When people first hear about reproductive biologist Jane Fenelon’s research their first reaction is shock, but also, curiosity. “It’s amazing how many people have actually heard that there’s something weird about the echidna penis,” she says. “For those less informed, Jane then follows this up with an image of an echidna penis, and the feelings of shock roll back. 

In late April, Jane and her colleagues published an in-depth research paper on the echidna penis. Labelled one of the “weirdest penises of the animal kingdom” by Smithsonian Magazine, the echidna penis is bright red and has four heads. ​”We’re not really sure why it looks so weird but we do know that they only use their penis for mating, not urine,” Janes says. “Because they don’t need it for urine, they had the freedom to make it much more elaborate and this is something you see in other species that only use it for mating.”

And while you may think we know all there is to know about the echidna, you’d be wrong.

The difficulty in studying the echidna is well-documented. Peggy Rismller, who has been studying echidnas for more than 30 years, was the first to discover that echidnas were laying their eggs into a pseudo-pouch, rather than hatching their eggs in burrows like their fellow monotreme, the platypus. That discovery was only made in the early 1980s, and the reproductive lives of echidnas continues to be difficult to capture. 

Echidnas are a protected species, meaning scientists such as Jane can’t go around picking them up and prying at their reproductive systems. So, for this study Jane teamed up with Currumbin Wildlife Sanctuary on the Gold Coast, which operates a wildlife hospital. From it, Jane received echidnas, euthanised due to illness, to analyse.