page_title: Tyrannosauridae
section_title: Vision
hierarchical_section_title: Tyrannosauridae / Paleobiology / Vision
caption_attribution_description: English: Close up of "Sue" T-Rex replica skull at the Field Museum of Natural History in Chicago, IL.
context_page_description: Tyrannosauridae is a family of coelurosaurian theropod dinosaurs that comprises two subfamilies containing up to thirteen genera, including the eponymous Tyrannosaurus. The exact number of genera is controversial, with some experts recognizing as few as three. All of these animals lived near the end of the Cretaceous Period and their fossils have been found only in North America and Asia.
  Although descended from smaller ancestors, tyrannosaurids were almost always the largest predators in their respective ecosystems, putting them at the apex of the food chain. The largest species was Tyrannosaurus rex, one of the largest and most massive known land predators, which measured over 12.3 metres in length and according to most modern estimates 8.4 metric tons to 14 metric tons in weight. Tyrannosaurids were bipedal carnivores with massive skulls filled with large teeth. Despite their large size, their legs were long and proportioned for fast movement. In contrast, their arms were very small, bearing only two functional digits.
  Unlike most other groups of dinosaurs, very complete remains have been discovered for most known tyrannosaurids.
context_section_description: The eye-sockets of Tyrannosaurus are positioned so that the eyes would point forward, giving them binocular vision slightly better than that of modern hawks. While predatory theropods in general had binocular vision directly in front of their skull, tyrannosaurs had a significantly larger area of overlap. Jack Horner also pointed out that the tyrannosaur lineage had a history of steadily improving binocular vision. It is hard to see how natural selection would have favored this long-term trend if tyrannosaurs had been pure scavengers, which would not have needed the advanced depth perception that stereoscopic vision provides. In modern animals, binocular vision is found mainly in predators (the principal exceptions are primates, which need it for leaping from branch to branch). Unlike Tyrannosaurus, Tarbosaurus had a narrower skull more typical of other tyrannosaurids in which the eyes faced primarily sideways. All of this suggests that Tarbosaurus relied more on its senses of smell and hearing than on its eyesight. In Gorgosaurus specimens, the eye socket was circular rather than oval or keyhole-shaped as in other tyrannosaurid genera. In Daspletosaurus, this was a tall oval, somewhere in between the circular shape seen in Gorgosaurus and the 'keyhole' shape of Tyrannosaurus.
caption: The eye-sockets of T. rex faced mainly forwards, giving it good binocular vision
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