(The world's first known fingernails belonged to a now-extinct primate, but the animal would have resembled the modern mouse lemur, pictured above. Credit: David Haring/Duke Lemur Center)

The world's oldest known fingernails would have been a challenge for today's manicurists: they were incredibly tiny and probably quite dirty.

The prehistoric fingernails, described in the current issue of the American Journal of Physical Anthropology, date to about 55.8 million years ago and belonged to a primate, now extinct, named Teilhardina brandti. This little lemur-like mammal measured just 6 inches long and lived in trees.

Co-author Jonathan Bloch told Discovery News, "While we are not sure about the original function of nails in primates, it seems clear that they evolved within the context of living in the trees, possibly associated with specialized grasping behaviors for moving in small diameter branches and manipulation of small food items (fruit, seeds, etc.)."

Bloch is an associate curator of vertebrate paleontology at the Florida Museum of Natural History on the University of Florida campus.

The early fingernails didn't look like our nails either, especially when we artistically tinker with them.

(French manicure, Wikimedia Commons image)

"They are not exactly shaped like our nails," Bloch said. "They are flat like ours, but longer and more claw-like than ours. This likely reflects the derivation of nails from an ancestor with claws (something like a tree shrew). It is our hypothesis that we can trace the origin of our own nails back to at least this point."

He and his colleagues made the discovery after studying more than 25 new specimens of T. brandti.

(Yale University doctoral student and University of Florida visiting scientist Stephen Chester, left, and Jonathan Bloch analyze fossilized teeth of Teilhardina brandti, the earliest North American species of euprimates, or "true" primates. Florida Museum of Natural History/Kristen Grace.)

These fossils were collected over the last seven years in northwestern Wyoming's Bighorn Basin. During the lifetime of this primate, the early Eocene epoch, a 200,000-year global warming event known as the Paleocene-Eocene Thermal Maximum occurred. Mammals evolved to be smaller then. It's also when the ancestors of deer and horses likey first emerged.

Deer and horses have hooves, but humans and all modern primates sport nails on their fingers and toes. We have many things in common with our fellow primates, and another shared feature is finger pads. They allow for sensitive touch and the ability to grasp, among other uses.

(A Smithsonian Museum specimen of Teilhardina brandti’s upper jaw, top, is compared to a Florida Museum of Natural History specimen of the skull of a tarsier, a lemur-like animal from Southeast Asia. You can see how small the primate with the first known fingernails was, given that it had such a tiny jaw. Credit: Florida Museum of Natural History/Kristen Grace.)

"If you take all the primates that are alive today, they’re all going to have characteristics that look the same, but unlike people, many of them live in trees," Bloch said. "By finding parts of the skeleton of this primitive primate, we are able to test whether nails were present in the common ancestor of the group that includes lemurs, monkeys, and humans — it’s direct evidence as opposed to speculation."

The findings counter prior speculation that the first fingernails might have emerged on larger primates.

"They are the smallest true nails known on record, whether living or fossil," lead author Ken Rose, a professor in the Center for Functional Anatomy & Evolution at Johns Hopkins University School of Medicine, said in a UF press release. "That certainly doesn’t suggest nails developed with larger bodies."