The limar of Madagascar is a sweet aberration of an animal.
There are huge ears, a thick tail, mammary glands between the legs and white hairs that flutter when excited. Above the vampiric nose and mouth of incisors that never stop growing, corn-colored eyes glow like full moons. His fingertips, closed in curved nails, cross his arms. The middle finger, the spindle rod, rotates on a pivot. Sometimes it folds into an even longer fourth finger.
If they weren't enough to fulfill the quota for eccentric adaptations, the scientists just found another – a secret spare thumb. This pseudo thumb, as it is called, even has a fingerprint.
Other animals also have additional appendages. But the ah-ay's spare thumb, described Monday in the American Journal of Physical Anthropology, may have evolved in circumstances not yet observed in other animals. The study shows that there is much more to learn about how different lines of vertebrate animals have evolved – even by looking at the anatomy we thought we understood.
A century of study and multiple X-rays overlooked the pseudo-thumb of ah-ah. Dr. Hartstone-Rose and his team discovered by accident when examining the muscles of the forearm. They followed a muscle that attaches to the arms of all primates for mobility, but were surprised to find small tendons that also connect it to the palm and button between the thumb and the wrist with cartilage extension.
"We realized that there were these different muscles that controlled this whole thing," says Dr. Hartstone-Rose, allowing the structure to move away from and to other fingers as well as in the palm of his hand.
They confirmed that this structure exists in seven total yes, suggest that it is part of the anatomy of mammals. And the reason for this seems to be related to his particular food-gathering technique.
At night hunters can fish using echolocation. They pat branches with slender fingers and listen to gaps in the forest. When the branch bounces back a hollow howl – insect tunnels intersecting under the bark – the lemur bites and tears the flesh of the tree. He inserts his rotating middle finger into the hole and spins it around, removing the cakes with his fingernails.
While these long, delicate fingers are perfect for picking a fountain, they are very disgusting. If the animal tries to use the middle finger to travel, it will click under the weight of aye-aye.
The hands of ahh became so specialized in feeding the faucet that they "lost the ability to grasp," Dr. Hartstone, "said Rose. According to him, they compensated with pseudo thumbs.
If the researchers confirm their hypothesis by studying the casts that live in the center of Duke Lemur in Durham, North Carolina, they will be the first animal described to have evolved an extra figure for dexterity due to a hyper-specialized trait.
In other cases, animals develop additional numbers to compensate when their fingers become less specialized or to extend their arms. For example, the original thumb became just another finger for the bear species, but the giant panda developed a pseudo thumb because it helped with eating bamboo. And the extra numbers made the moles better diggers.
But yes, aye cannot stay alone for a long time: "We are beginning to look at some of the structures of bats in bats," says Dr. Hartstone-Rose. "We think they have some similar types of little grasping accessories that they have added to their wrists."