|Source Maiolino et al. 2012 PLoS ONE|
Recently in PLoS ONE: a study providing evidence that the early Eocene primate Notharctus tenebrosus had a transitional grooming claw on its second digit. Grooming claws are important because they are a classic feature which distinguishes between anthropoid primates (monkeys, apes, and humans) and prosimian primates (primates with a grooming claw: tarsiers, lemurs, lorises, etc). Certain European fossil adapiform primates have controversially been claimed to have a nail, thus linking them with anthropoids. This new study describes a grooming claw on the foot skeleton of a North American adapiform, and its grooming claw is quite nail-like with a wide apical tuft. This might be seen as further evidence supporting a link between adapiforms like Darwinius with anthropoids, except for the fact that a thorough cladistic analysis links adapiforms (including Darwinius) with strepsirrhines (lemurs and lorises). Thus, the authors conclude that there may have been substantial homoplasy in the second pedal digit, with multiple taxa evolving nails.