The aye-aye’s fourth finger accounts for more than two-thirds the length of its hand if humans had such a digit, it would be nearly a foot long. The team hypothesises that throughout evolution, the aye-aye lost some ability to grip due to the extreme specialisation of its other fingers. Such studies of arm and hand anatomy, and the differences between lineages, could help better understand how these structures have evolved in different species, including humans. “It’s really cool to find this kind of anatomy in a primate for the first time, especially a primate as weird as an aye-aye,” Hartstone-Rose says. Hartstone-Rose and colleagues have named this a “pseudo-thumb,” and suggest that it functions as sixth digit to help the arboreal animals hold onto tree limbs. Further investigation revealed two other muscles are connected to the radial sesamoid, which allow the bone to move in a gripping motion. The bone is also topped, the team reported in a study published October 21 in the American Journal of Physical Anthropology, with an extension of cartilage. But in the aye-aye, part of it splits off, and connects with a bone called the radial sesamoid, which is usually quite small in other primates, but elongated in this endangered species. In most primates, it starts in the forearm and attaches to the base of the thumb. “It’s the muscle that allows you to hitchhike,” he says. This is one that, in humans, extends the thumb away from the body, a motion called abduction. They then gnaw into the bark with rodent-like incisors, and remove the goods with their chopstick-like digits.Įxamining the aye-aye specimen, Hartstone-Rose and colleagues began to trace the route of a muscle called the abductor pollicis longus down into the forearm. Their brains, the largest of any lemur relative to body mass, allow them to find the larvae’s tunnels. These house cat-size lemurs, native to Madagascar, have super-long, spindly third and fourth fingers that they use to tap on trees to find grubs. The aye-aye ( Daubentonia madagascariensis), if you’re unfamiliar, is one of nature’s more absurd creations. “They have these famously strange hands and bizarre fingers,” he says-all the better for research. When his lab at North Carolina State University happened across a dead aye-aye specimen, he was thrilled. The delicate movements of our hands, for example-like the ability to play a Mozart piano concerto-are only possible thanks to these sinews.īut Hartstone-Rose doesn’t study only human forearms: he specialises in those of many primates, and comparing anatomical differences between species. Adam Hartstone-Rose studies the muscles of forearms, which are surprisingly intricate and easily overlooked.
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