One of the most inexperienced and weirdest lemurs in the world has just escalated the weirdness. The animal has six digits on its hands, making it the only known primary species to sport a "pseudothumb" hiding in the wrist of each arm.
However, it does not wrong its hidden nature for uselessness. The little extra thumb has three degrees of motion, just like the ordinary thumb; can exert great force and even have its own imprint.
Aye-aye (Daubentonia madagascariensis), born in Madagascar, are completely, very strange. They have big round eyes and huge ears, better suited to their nightlife. Their fur is dense and white in color, giving them a ravenous appearance.
And then there are the hands, with long, swivel fingers. One finger on each side extends centimeters longer than the other: an evolutionary adaptation to reach hollow logs and scatter the juicy lumps inside.
"Ie is the craziest hand on any primary," said biologist Adam Hartston-Rose of North Carolina State University.
"Their fingers have evolved to be extremely specialized – so specialized, in fact, that they don't help much when moving through the trees. When you see them moving, it looks like a strange lizard walking on spiders. "
Hartston-Rose, whose research lab specializes in comparative biology and functional morphology, studied the tendons in Eye's arm with colleague Edwin Dickinson when they noticed an unusual needle in the wrist.
Using digital imaging techniques – where 3D digital scanning of an animal's body can be studied in detail without destroying said body part – researchers have studied the hands of six ayas, male and female, at a range of ages, from juvenile to adult.
They found the digit, which they identified as a pseudonym, on both hands of all six animals.
"The pseudonym is definitely more than just a rosary," said Hartston-Rose.
"There's also a bone extension and a cartilage and three different muscles that move it. The pseudoma can get into space and exert an amount of force equal to almost half the weight of aye-aye. So it would be useful for capture. "
The figure is not unprecedented, though it marks a unique finding for primates. The most famous, the giant panda (Ailuropoda melanoleuca) has such a pseudobulb structure that holds itself out of its wrist, which it uses specifically to capture the bamboo it eats.
Digging moles also grow a second thumb from the joints. It's not about catching in this case; the pseudonym extends the notebook to animals, probably to make them more efficient blades. And some frogs have pseudonyms, increasing their numbers to five of the usual four we see in frogs.
Usually, there seems to be an advantage to these extra digits. So the researchers are probably right about the island, too.
"In this case, aye-aye's hand is so specialized in getting an extra digit of mobility," said Hartston-Rose.
"Some other primary species have reduced numbers to help locomotion.
"And it is amazing that he is there all the time, in this weirdest of all primates, but no one has ever noticed it."
The research is published in American Journal of Physical Anthropology.