Evolution of primate special senses

Abstract

The origin and early cladogenesis of primates involved several critical shifts in sensory anatomy and ecology. Comparisons of living and fossil euarchontans suggest that the origin of crown primates was associated with the evolution of (a) increased eye size and (b) greater optic convergence. Functional and comparative evidence indicates that these features are best explained as adaptations for increased visual acuity and improved depth perception in the context of nocturnal visual predation. A second major shift in primate sensory anatomy occurred with the origin of crown Haplorhini. Most living haplorhines share a suite of highly derived adaptations for enhanced visual acuity, including (a) small corneas relative to eye size, (b) a retinal fovea, and (c) a postorbital septum. Haplorhines also demonstrate a derived reduction of the olfactory apparatus, including (a) loss of the rhinarium, (b) loss of an olfactory recess in the nasal cavity, and (c) decreased olfactory bulb size. While the underlying causes of olfactory reduction remain obscure, enhanced visual acuity likely evolved in haplorhines as an adaptation for visually directed predation in a diurnal setting.