The mystery of the bony growth on an elephant’s foot has been solved by scientists, who have discovered it is actually a prehistoric sixth “toe.”
Previously, the lump was thought to have been an errant piece of cartilage, but the 5-10 cm long peculiarity is actually a bone, which helps support the gigantic animals.
Although elephants look flat-footed, this appearance is because their heel rests on a massive pad of fat. Like horses and dogs, elephants actually stand on tip-toe.
“The elephant foot is deceptively complex.” Matthew Vickaryous, an independent vertebrate morphologist at the University of Guelph in Canada told Wired.
“The unique structure of the foot must clearly be considered a key innovation,” he said.
The sixth “toe” is hidden beneath the foot. Unlike the elephant’s “normal” five toes which point forward, the sixth digit points backwards into the fatty flesh of the sole.
It’s not a real “toe” but like pandas and moles, the evolutionary quirk helps the animal thrive. The panda appendage helps the monochrome bear grip bamboo, while the mole's "toe" helps the dirt-thrower dig.
Although the elephant “toe” was first suggested more than 300 years ago, by Patrick Blair - a Scottish doctor, elephants are notoriously difficult to study.
Elephant’s react poorly to anaesthesia and X rays often fail to penetrate the foot of the pachyderms, whose skin is about an inch thick.
However lead author Professor John Hutchinson, from the UK's structure and motion laboratory at the Royal Veterinary College used dead elephant feet, which he amputated after receiving the cadavers from zoos.
He told Nature.com: “Fortunately, I have the dubious distinction of having perhaps the world’s largest collection of frozen elephant feet.” Hutchinson has sixty altogether, having studied the toe for more than three years.
He told the BBC: "It is a great example of how evolution tinkers and tweaks tissue to provide different functions - in this case to be co-opted to be used like a digit."
The research is published in the journal Science.