Binocular vision in theropod dinosaurs

ABSTRACT

The binocular fields of view of seven theropod dinosaurs are mapped using sculpted life reconstructions of their heads and techniques adopted from ophthalmic field perimetry. The tall, narrow snout and laterally facing eyes of the allosauroids Allosaurus and Carcharodontosaurus restricted binocular vision to a region only approximately 20° wide, comparable to that of modern crocodiles. In contrast, the coelurosaurs Daspletosaurus, Tyrannosaurus, Nanotyrannus, Velociraptor, and Troodon had cranial designs that afforded binocular fields between 45–60° in width, similar to those of modern raptorial birds. Binocular field width and predatory style (ambush versus pursuit) is examined for extant taxa, along with a discussion of cranial adaptations that enhance binocular vision. The progressive increase in frontal vision in the tyrannosaurids culminates in broader binocular overlap than that of a modern hawk. The visual acuity and the limiting far point for stereopsis is estimated for Tyrannosaurus based on reptilian and avian models.