In a manicured Ted Ed lesson written by Matthew Borths and animated by Nabil Buris, narrator Addison Anderson explains the difference between nails and claws. He further goes into which animals evolved to have nails instead of claws and how each form of hardened keratin serves a unique purpose for each animal.
The primary difference between the two keratin coverings is really just their shape, which depends on the shape of the bone at the end of the animal’s digits. In claws, the bed of keratinocytes conforms to a narrow finger bone, wrapping around the end of the digit and radiating outwards to form a cone-shaped structure. Animals with nails, on the other hand, have much broader digits, and keratinocytes only cover the top surface of their wide bones. It’s possible that nails have simply persisted as a side effect of primates evolving wider, more dexterous fingers. But given what we know about the habitats of our primate ancestors, it’s more likely that nails came with their own powerful advantages.