Newly discovered fossil evidence has overridden the previous assumption that ancient primates only had nails on their fingers and toes.

The findings, which were published in the Journal of Human Evolution Wednesday, suggest the lineage of primates leading up to mammals, such as monkeys, apes and humans, had a specialized claw.

The claw, called a “grooming claw,” functions as a personal primping tool. It has been found in a separate lineage of primates that evolved into animals like lemurs, galagos and tarsiers.

Curator at the Florida Museum of Natural History and coauthor on the study Jonathan Bloch said apes, monkeys and humans don’t have grooming claws because they developed complex social structures and can rely on others for grooming.

Monkeys, apes and humans are all united by having that one feature, which is nails,” said Bloch.

Learning how nails evolved in primates helps us understand why humans have “that very special type of characteristic,” Bloch said.

The research team found the fossils across Wyoming, including in an area by Yellowstone National Park. They ranged from 46 to 56 million years old, which Bloch said is around the same age as the oldest-known primates in the modern era.

They discovered bones similar to distal phalanges, the bones at the ends of fingers and toes in mammals, which have either claws or nails, Bloch said.

He immediately realized the bones were not flat and wide to support nails. In fact, the distal phalanges were tapered and clawlike, resembling a grooming claw.

“We knew we had something special because before that, we had thought that the first primates of (the) modern aspect would (have) had nails on all their fingers and toes,” Bloch said. “To see a claw on one of the digits really went against that sort of thinking.”

Bloch said having a nail instead of a claw is a hallmark characteristic of primates. The lack of claws allows for better precision grasping — ideal for tree-dwellers like monkeys and apes.

(The fossilized evidence) helps give us a better picture of what the common ancestor of all living primates look like,” said UF graduate student in the Department of Anthropology and member of the study Paul Morse. “We ran across unexpected but important evidence for this trait in early primates.”

Bloch and Morse hope the study’s findings will result in new fossil collections and future field work to uncover information about our ancestors.

Follow Dana Cassidy on Twitter @danacassidy_ and contact her at [email protected].