The Therizinosaurus is one of the most unusual and visually striking dinosaurs known to science. Its bizarre combination of a large body, long neck, and impossibly long claws often leads people to wonder if the “scythe lizard” is a real creature or merely a fantastical invention. This animal did indeed walk the Earth, and its remains have helped reshape our understanding of dinosaur evolution.
Confirmation and Geological Context
Therizinosaurus is real, though its discovery was initially confusing. The first fossil evidence was unearthed in 1948 during a Soviet-Mongolian expedition in the Gobi Desert of Mongolia, specifically within the Nemegt Formation. This region represents a terrestrial ecosystem from the Late Cretaceous period, approximately 70 million years ago.
The original find consisted primarily of only a few gigantic claw bones. These were so unusual that paleontologist Evgeny Maleev first described them in 1954 as belonging to a large, turtle-like reptile. Scientists did not recognize the creature as a unique type of dinosaur until later discoveries of more complete, related specimens in the 1970s and 1980s.
Decoding the Anatomy of Therizinosaurus
The body structure of Therizinosaurus was slow-moving and robust. It possessed a proportionally small skull atop an unusually long neck, suggesting it was adapted for high browsing. The torso was deep and wide, providing space for a large gut to process vegetation.
Unlike most theropods, which walked on three functional toes, Therizinosaurus had four functional, weight-bearing toes on its hind limbs. While no direct evidence of feathers has been found on this species, related species like Beipiaosaurus preserve evidence of simple, single-filament proto-feathers. Based on this phylogenetic evidence, modern reconstructions often depict Therizinosaurus as possessing a coat of primitive feathers.
The Function of the Massive Claws
The most iconic feature of this dinosaur is the massive size of its manual claws, which were among the longest of any known animal. These scythe-like unguals could reach lengths well over 50 centimeters, potentially up to one meter long. The robust arms suggest they resisted significant stress during use.
One leading theory proposes the claws were used for foraging in a “hook-and-pull” fashion, grasping and pulling large branches or shrubs down toward its mouth for feeding. This behavior is similar to that seen in modern sloths.
The claws may have also served a purpose in social behavior and defense. Their fragility suggests they were not ideal weapons for active combat. Instead, they might have functioned as an impressive display feature for intimidation during territorial disputes or as a deterrent against large predators, such as the contemporary tyrannosaur Tarbosaurus.
Diet and Evolutionary Puzzle
Despite its descent from predatory ancestors, Therizinosaurus was almost certainly a herbivore, a surprising finding for a member of the Theropoda group. Evidence for this plant-based diet comes from its relatives, which possessed small skulls equipped with a horny beak and small, leaf-shaped teeth. The wide, pot-bellied torso is consistent with the need for a large digestive tract to process tough vegetation efficiently.
This dietary shift from carnivory to herbivory is a major evolutionary puzzle, showcasing adaptability within the dinosaur lineage. The anatomical changes, including the development of a wide pelvis, were necessary to support the large gut and the slower pace of a plant-eater. This combination of features represents a case of convergent evolution, resulting in a body plan that superficially resembles ancient mammals like ground sloths.