The massive, scythe-like claws of Therizinosaurus cheloniformis make it one of the most distinctive dinosaurs of the Late Cretaceous period. Measuring up to three feet long, these unusual features gave the animal its name, which translates to “scythe lizard.” This colossal herbivore was a member of the theropod group, but unlike its carnivorous cousins, it was a slow-moving, feathered plant-eater that could reach lengths of 33 feet and weigh over five tons.
The unique anatomy of this dinosaur, particularly its relatively small skull atop a long neck, raises questions about how it perceived its world. Understanding its sensory capabilities requires looking beyond its remarkable claws to the subtle clues preserved within its fossilized remains.
The Myth of Therizinosaurus Blindness
The idea that Therizinosaurus was blind is a notion largely popularized by recent media depictions, which portrayed a specific specimen with eye afflictions. This dramatic portrayal suggested the dinosaur navigated its environment using only sound and smell, but scientific evidence indicates this was not the reality for the species as a whole. Paleontological studies suggest that therizinosaurs, including the closely related Erlikosaurus, possessed highly developed senses, including a good sense of sight.
The vision of this large herbivore was certainly functional, though not necessarily keen in the same way as that of a fast-moving predator. Its visual system was likely specialized for its lifestyle, which involved high browsing and slow movement. The eyesight would have been sufficient for distinguishing large shapes, detecting movement, and locating suitable patches of vegetation for foraging and survival.
Anatomical Clues to Therizinosaurus Vision
Paleontologists determine the visual capabilities of extinct animals by analyzing the bony structures. The size and position of the orbit offers initial clues about the size of the eyeball and the animal’s field of view. In therizinosaurs, the large orbit suggests a sizable eye, which is correlated with better visual acuity and sensitivity to light.
The skull structure of related therizinosaurs suggests their head posture allowed for some overlap in the visual fields, providing a degree of binocular vision. A more precise method for inferring visual habits involves examining the scleral ring, a bony ring within the eye found in many reptiles and birds. The ratio between the inner and outer diameters of this ring indicates the eye’s light-gathering ability. Analysis of these structures suggests they were likely cathemeral, meaning they were active throughout both the day and night.
Sensory Life Beyond Sight
Since Therizinosaurus was not a highly visual hunter, it relied on other well-developed senses to navigate its world and detect threats. Evidence from endocranial casts of related species reveals that therizinosaurs possessed a strong sense of smell. The olfactory bulbs, the parts of the brain responsible for processing scent, were enlarged, suggesting olfaction was a primary sensory tool.
A powerful sense of smell would have been invaluable for an herbivore, helping it locate nutrient-rich food sources or detect distant predators like the tyrannosaur Tarbosaurus. The inner ear structure in theropods provides insight into their hearing and sense of balance. Large, slow-moving dinosaurs often possess a hearing range optimized for lower frequencies, which travel farther. This ability enabled Therizinosaurus to perceive ground vibrations and hear threats approaching from long distances.