Grooming claw

Close-up of a ruffed lemur's foot, showing the toilet-claw on the second toe and nails on all other toes

A grooming claw (or toilet claw) is the specialized claw or nail on the foot of certain primates, used for personal grooming. All prosimians have a grooming claw, but the digit that is specialized in this manner varies.^[1] Tarsiers have a grooming claw on second and third toes. With one possible exception, in the suborder Strepsirrhini, which includes lemurs, galagos and lorises, the grooming claw is on the second toe. The possible exception is the aye-aye, which has claws instead of nails on toes 2 through 5. There is some debate concerning whether any of these claws (and if so which ones) are grooming claws. Less commonly known, a grooming claw is also found on the second pedal digit of night monkeys (Aotus), titis (Callicebus), and possibly other New World monkeys.^[2]

The first toe is the large one, the equivalent of a human big toe. However, in all these prosimians the foot is more or less hand-like. The first toe is opposable, like a human thumb, and the second and third toes correspond approximately to the index and middle fingers.

Like a claw or a nail, the grooming claw is also made of keratin. It resembles a claw in both its lateral compression and longitudinal curvature. However, the tip is not as pointed, and it always stands at a steeper angle, a characteristic that also distinguishes it from a nail.^[1]

Function

The grooming claw is used in personal grooming to rake through the fur or scratch, particularly around the head and neck.^[2]

References

1. Soligo, C.; Müller, A. E. (1999). "Nails and claws in primate evolution". Journal of Human Evolution 36 (1): 97–114. doi:10.1006/jhev.1998.0263. PMID 9924135.
2. Maiolino, S.; Boyer, D. M.; Rosenberger, A. (2011). "Morphological Correlates of the Grooming Claw in Distal Phalanges of Platyrrhines and Other Primates: A Preliminary Study" (PDF). The Anatomical Record 294 (12): 1975. doi:10.1002/ar.21498.