A backward view of visual adaptations: cranial specialization and predator evasion within a cursorial mammal

Abstract The evolution of the vertebrate visual system involves numerous biological systems, and may include field of view (FOV) transformations linked to changes in eye position within the cranium. Overall, FOV orientations are driven by ecological factors such as habitat, locomotor mode and foraging techniques. Rabbits typically have a divergent, wide FOV and are characterized as looking sideways, contrasted with the convergent, forward-looking orientations of humans. Under-appreciated morphological variation in the rabbit skull, particularly in facial tilt angles related to locomotory mode, suggests greater diversity in rabbit FOV than previously shown. To test this, we capture orbit orientations using landmark-based morphometric methods on a large existing digital skull dataset that represents all genera and most species of crown leporids. We find strong evolutionary relationships between downward facial tilting and the position of their orbits. Cursorial species tilt their faces more ventrally (e.g. most Lepus spp.), and their orbits are more divergent. Leporid species also exhibit a wide range of orbital vergence angles, similar to primates. We propose that leporid cranial specializations, such as facial tilt and divergent orbit positions, modify their FOV to allow them to better evade predators by capturing a complete view of their environment at the horizon.