Ancient primates had grooming claws as well as nails ... what happened to ours?

Grooming claws
CC BY 2.0 Kristen Grace/Florida Museum

Ancient primates had all the fun.

As you can see in the photo above – paw shots of of two greater slow lorises, Nycticebus coucang, in the Florida Museum mammals collection – creatures like lemurs, lorises and galagoes have nails on most digits and bonus grooming claws on their second toes.

Wouldn't that be an amazing little tool to have built right in? No reaching for a knife to open a package, always having a sharp object on hand, so to speak, for protection ... and combs would be a thing of the past!

In fact, the handy built-in grooming claw is a pretty essential tool for primates. What with all the ticks and lice and other parasites – having a specialized claw for removing them would be an evolutionary advantage, says Doug Boyer, an associate professor in the department of evolutionary anthropology at Duke University and the lead author of a new study on the matter. So what happened to ours?

Humans and other primates are unique in the mammal world for having our digits graced with nails instead of claws. It's long been assumed that our earliest primate relatives had nails on all their digits, but with the recent discovery of fossils showing tiny grooming claws as well as nails on one of the oldest known primates, Teilhardina brandti, the story line has changed, according to Boyer's study.

"We had just assumed nails all evolved once from a common ancestor, and in fact, it's much more complicated than that," Jonathan Bloch, study co-author and the Florida Museum of Natural History's curator of vertebrate paleontology, notes in a news release from the University of Florida.

Grooming clawsKristen Grace/Florida Museum/CC BY 2.0

So, why did our primate ancestors lose their grooming claws? The researchers suggest that one reason could be because we started grooming each other.

"The loss of grooming claws is probably a reflection of more complex social networks and increased social grooming," Boyer said. "You're less reliant on yourself." Which could also explain why more solitary monkey species, like titi and owl monkeys, have re-evolved a grooming claw, he added.

While researchers initially believed that grooming claws developed independently several times along the lines that went on the become living primates, these fossils suggest that grooming claws were important features of the earliest primates, going back at least 56 million years.

While I think grooming claws are rad, in the grand scheme of things they may not seem like such a big deal. But they can provide important insights into ancient primates, many of which are known only from fossil teeth, Bloch said. These itty-bitty claws reveal secrets about how our earliest ancestors moved through their environment, whether they were social or solitary and what their daily behavior was like.

"We see a bit of ourselves in the hands and feet of living primates," Bloch said. "How they got this way is a profoundly important part of our evolutionary story."

Models of the fossils are available on Morphosource, an open-access repository of 3D data directed by Boyer.

Ancient primates had grooming claws as well as nails ... what happened to ours?
Ancient primates had all the fun.

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