Strange long-fingered aye-aye lemur has a hidden SIXTH digit

Considered one of the world’s oddest animals, the aye-aye has just gotten even weirder after scientists discovered a sixth finger hiding in plain sight.

The six-fingered Madagascan lemur has become the first primate to be found with an extra digit.

New research has found that the aye-ayes have tiny sixth fingers called ‘pseudothumbs’ – complete with their own fingerprints – that may help them grip objects and branches as they move through trees.

New research has found that the long-fingered lemurs from Madagascar have tiny sixth fingers called ‘pseudothumbs’

The extremely rare lemurs have constantly growing teeth, large ears, and strange hands with a slender, long middle fingers that they use for tapping on trees to find grubs before digging in with their teeth and spearing their prey.

Some local people believe the bizarre creatures are the harbingers of doom and that their appearance in a village is a sign a resident will die.

Others think they sneak into homes through thatched roofs and kill the occupants in their sleep by puncturing their hearts with their long middle finger.

Professor Adam Hartstone-Rose, of North Carolina State University in the US, said: ‘The aye-aye has the craziest hand of any primate.

‘Their fingers have evolved to be extremely specialised – so specialised, in fact, that they aren’t much help when it comes to moving through trees. When you watch them move, it looks like a strange lemur walking on spiders.’

Prof Hartstone-Rose and NC State post-doctoral researcher Edwin Dickinson were studying the tendons that lead to the aye-aye’s unusual hands when they noticed that one of the tendons branched off toward a small structure on the wrist.

The pair dissected six aye-ayes, and used digital imaging and worked out that the digit moved a lot like a human thumb.

A rare black aye-aye named Melisandre born at Duke Lemur Centre, North Carolina, USA

It is the first extra digit ever found in a primate.

Prof Hartstone-Rose said: ‘The pseudothumb is definitely more than just a nub. It has both a bone and cartilaginous extension and three distinct muscles that move it.

‘The pseudothumb can wriggle in space and exert an amount of force equivalent to almost half the aye-aye’s body weight. So it would be quite useful for gripping.’

The team examined male and female aye-ayes of all ages and found the same finger in both the left and right hands of each one.

Prof Hartstone-Rose and Dr Dickinson believe the aye-aye could have developed the pseudothumb to grip – something its other specialised fingers can’t do.

Prof Hartstone-Rose added: ‘Other species, like the panda bear, have developed the same extra digit to aid in gripping because the standard bear paw is too generalised to allow the dexterity necessary for grasping.

Superstitious villagers in Madagascar believe the animals sneak into homes through thatched roofs and kill the occupants in their sleep by puncturing their hearts with their long middle finger

‘And moles and some extinct swimming reptiles have added extra digits to widen the hand for more efficient digging or swimming.

‘In this case, the aye-aye’s hand is so specialised for foraging an extra digit for mobility became necessary.

‘Some other primate species have reduced digits to aid in locomotion.

‘The aye-aye is the first primate to dial digits up in the hand rather than dial them down.

‘And it’s amazing that it’s been there the whole time, in this strangest of all primates, but no one has noticed it until now.’

The findings were published in the American Journal of Physical Anthropology.