Adam Hartstone-Rose studies the muscles of forearms, which are surprisingly intricate and easily overlooked. The delicate movements of our hands, for example—like the ability to play a Mozart piano concerto—are only possible thanks to these sinews.

But Hartstone-Rose doesn’t study only human forearms: he specialises in those of many primates, and comparing anatomical differences between species. When his lab at North Carolina State University happened across a dead aye-aye specimen, he was thrilled. “They have these famously strange hands and bizarre fingers,” he says—all the better for research.

The aye-aye (Daubentonia madagascariensis), if you’re unfamiliar, is one of nature’s more absurd creations. 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. Their brains, the largest of any lemur relative to body mass, allow them to find the larvae’s tunnels. They then gnaw into the bark with rodent-like incisors, and remove the goods with their chopstick-like digits.

Examining 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. This is one that, in humans, extends the thumb away from the body, a motion called abduction. “It’s the muscle that allows you to hitchhike,” he says.

In most primates, it starts in the forearm and attaches to the base of the thumb. 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.