Enigmosaurus, which translates to "Enigma lizard" or "Enigmatic lizard," is a therizinosauroid genus that inhabited Asia during the Late Cretaceous era. This medium-sized dinosaur was a herbivore that primarily walked on two legs and lived on the ground. It marks the third therizinosaur species discovered in the Bayan Shireh Formation, with its fossils originating from the lower section of the formation.

The genus consists of a single species, E. mongoliensis, identified from a remarkably well-preserved pelvis and some other potential body fragments. Enigmosaurus was a moderately large therizinosaur, measuring approximately 5 meters (16 feet) in length and weighing somewhere in the range of 454 to 907 kilograms (1,001 to 2,000 pounds).

The name "Enigmosaurus" was chosen because the initial discovery of its pelvis perplexed the paleontologists describing it, as it differed significantly from those of other dinosaurs. In reality, Enigmosaurus belongs to the therizinosaur group, a unique type of theropod dinosaur characterized by elongated necks and exceptionally long claws on their fingers. Being a therizinosaur, it was probably a herbivore or an omnivore.