Your fingernails and toenails are evidence that you are a primate, part of the group of mammals that includes lemurs, monkeys, and apes. Most mammals and reptiles have claws at the ends of their fingers and toes. Where did these nail things come from, and how did they help primates along our evolutionary journey?

Primate Adaptations
Primates are a group of mammals that have many adaptations for an arboreal (“tree-living”) lifestyle. In this video we explore nails, an adaptation that helps primates firmly grasp tree branches as they climb, but there are other traits that primates have that help them high off the ground.

Primates also have forward-facing eyes that help us perceive depth in three dimensions. Forward-facing eyes are possible because primates have relatively small snouts compared to many other mammals.

Primates also have relatively large brains for their body size, which help them navigate their complex environment and keep track of social relationships. These big brains also help primates interpret all the sensory information they are receiving from their nerve-infused, highly sensitive finger pads.

Finally, primates all have opposable thumbs and opposable big-toes. That means the pad of the first digit on a primate’s hand or foot can touch the pad of other digits. Humans are primates, but we lack opposable toes. We know from the structure of the muscles in our feet that our ancestors had grasping feet, but as our lineage adapted to walking on the ground, the big toe aligned with the rest of our toes to give us a solid platform and lever for vaulting us forward with each step.

Some other mammal groups have primate-like traits. Some possums have opposable thumbs and lack claws and cats have forward-facing eyes, but primates are the only group that combine all of these traits in one lineage.

Claws to Nails to Claws
One of the first nail-bearing primate relatives was Carpolestes. Carpolestes belonged a group of mammals called plesiadapiforms. It had an opposable big toe and nails on its feet, but not yet on its hands. A few million years later, the first true primates evolved, animals like Teilhardina and Notharctus. Based on the fossil record, paleontologists know the ancestors of all primates had nails on their hands and feet, but some primate lineages have retained a few claws, or re-evolved the structures. Marmosets and tamarins are small, South American monkeys that have long claws that help them scamper up large tree trunks like squirrels (squirrels are a type of rodent).
 
Lemurs are a group of primates that live in Madagascar. They have one claw on each foot that is called a “grooming claw” or a “toilet claw” because they use it to clean themselves. One lemur has more than a grooming claw: the aye-aye.

Aye-ayes – like marmosets – have only claws on their hands and no nails. Aye-ayes use these claws to help them skewer their insect prey. Aye-ayes hunt by listening for insects with their large ears, then burrowing into the tree trunk with their rodent-like, ever growing front teeth. They reach their fingers into the hole to fish out their food. Check out this video of an aye-aye feeding

If you have more questions about aye-ayes and other lemurs – including how to help these extremely endangered primates - send your questions to the folks at the Duke Lemur Center at Duke University

Why do I need to trim my fingernails?
Hair and nails are both derived from keratin. In keratinous structures active growth occurs at the base of the structure. Keratinous structures cannot repair themselves internally because they do not have nerves or a blood supply throughout their length. Bone – unlike keratin – has nerves and a blood supply that allows it repair itself. That means the only way to “repair” a nail or hair is to keep growing it out. Most animals wear down their nails or claws with use over time, so they don’t really need to trim them. They just extrude new nail and wear down old nail. If an animal does need to trim a claw or nail, they may bite it, just like we do, though we have also developed handy tools that help us trim our nails when it’s time.

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