The idea of a blind Therizinosaurus is often fueled by modern fictional depictions of this massive creature. This unique dinosaur raises questions about how it navigated its Late Cretaceous environment. The question of whether it was functionally blind is answered not by direct observation, but through scientific inference drawn from its preserved skeletal anatomy.
Basic Anatomy and Lifestyle
Therizinosaurus cheloniformis, meaning “scythe lizard,” was an exceptionally large dinosaur that lived approximately 70 million years ago in what is now Mongolia. Although it belonged to the theropod group, which includes carnivorous dinosaurs like Tyrannosaurus rex, Therizinosaurus was a specialized herbivore. This shift is reflected in its wide, robust body and small, long-necked head.
Its most defining feature was the enormous claws on its three-fingered forelimbs, which could reach lengths of up to one meter. These claws were likely used for pulling branches toward its mouth for stripping leaves, not for combat. Its immense size, up to five metric tons, suggests a relatively slow, deliberate movement.
Inferring Sensory Perception from Fossils
To understand the visual capabilities of extinct animals, paleontologists analyze the preserved structure of the skull, particularly the eye socket, or orbit. The orbit’s dimensions provide clues about the size and shape of the eyeball. A more specific piece of evidence is the scleral ring, a series of bony plates found in the eyes of many reptiles, birds, and dinosaurs.
This ring encircles the pupil and helps maintain the eyeball’s shape. By measuring the ratio of the inner ring aperture to the overall orbital diameter, researchers infer the amount of light the eye was adapted to receive. A larger aperture ratio suggests adaptation for low-light, indicating a nocturnal habit. This analysis allows scientists to categorize an animal’s daily pattern as diurnal, nocturnal, or cathemeral—active intermittently throughout both day and night.
What the Evidence Suggests About Its Eyesight
Current scientific evidence does not support the idea that Therizinosaurus was functionally blind; this claim is a fictional portrayal. Studies analyzing the skull of Erlikosaurus andrewsi, a close relative, suggest that these dinosaurs possessed excellent eyesight, along with a strong sense of smell and balance. The large orbital cavity found in therizinosaur skulls indicates that the eyes were substantial and capable of gathering sufficient light.
Analyses of scleral rings across various dinosaur groups suggest that most large herbivores, similar to modern megaherbivores, were likely cathemeral. This means they were active during both the day and night, likely requiring continuous foraging to sustain their enormous body mass. Given its immense size and slow nature, sharp, predatory vision was not required for survival. Its vision was likely adequate for navigation and locating abundant plant matter. The fossil record confirms that Therizinosaurus possessed the necessary anatomical structures for functional sight.