The ecology of touch: Are prosimians special?

The size of the infraorbital foramen (IOF), through which the infraorbital nerve (ION) passes, has been used to infer the number of vibrissae (whiskers) an animal has, which in turn has informed phylogenetic and ecological interpretations of extinct primates. The functional signi ficance of IOF area, however, has not been tested. I present a comparison of relative IOF area among extant mammals. My results show that (1) relative IOF area is a good indicator of ION size and thus of touch sensitivity of the rostrum; (2) primates and other euarchontans have low IOF areas relative to most other mammals; (3) IOF area and vibrissal count correlate, but not strongly; and (4) among primates IOF area covaries with diet, such that frugivores have relatively larger IOFs than do folivores or insectivores. This dietary signal holds for prosimians and anthropoids, and prosimians do not have enlarged IOFs compared with anthropoids.