Flying primates? Megabats have the advanced pathway from eye to midbrain.

The pattern of connections between the retina and midbrain has been determined with electrophysiological and neuroanatomical methods in bats representing the two major subdivisions of the Chiroptera. Megachiropteran fruit bats (megabats), Pteropus spp., were found to have an advanced retinotectal pathway with a vertical hemidecussation of the kind previously found only in primates. In contrast, the microchiropteran bat Macroderma gigas has the "ancestral" or symplesiomorphous pattern of retinotectal connections so far found in all vertebrates except primates. In addition to linking primates and megachiropteran bats, these findings suggest that flight may have evolved twice among the mammals.