Which came first, the nail or the claw?

Chris Gash 

"The answer is unclear, but researchers have discovered a clue: an early primate that had a toe bone with features of both a grooming claw and a nail. A fossil of the 47-million-year-old primate, Notharctus tenebrosus, had a lemur-like grooming claw on its second digit, but it was flattened, a bit like a nail, according to a new study in the journal PLoS One. “What it really looks like is an intermediate morphology between grooming claw and a nail-like structure,” said an author of the study, Jonathan I. Bloch, curator of vertebrate paleontology at the Florida Museum of Natural History. “It’s perhaps catching evolution in action.” The toe bone specimen was collected more than a decade ago, but was sitting unprepared in a block of rock at the American Museum of Natural History in Manhattan. “We took that block and CT-scanned it,” Dr. Bloch said. “The scan revealed that there was a semiarticulated foot.” What is not clear is whether  the structure is a nail morphing into a claw, or a claw morphing into a nail. In the past, primates without a grooming claw were classified as anthropoids, along with humans, monkeys and apes. Those with claws are thought to be more like lemurs. The discovery of the toe bone on Notharctus is important, Dr. Bloch said, because it has been proposed as a possible ancestor of humans."
 NYTimes.com