Discovered in the Morrison Formation of North America, Nanosaurus belongs to the broader category of ornithopod dinosaurs. While its classification has undergone revision over time, it is typically considered a member of the Hypsilophodontidae family, a diverse group of herbivorous dinosaurs known for their small size and rapid mobility.

Nanosaurus was a small dinosaur, measuring around 2-2.2 meters in length and weighing approximately 20-30 kilograms. Its skeletal structure suggests adaptations for swift movement, with relatively long hind limbs and a lightweight build. Despite its diminutive size, Nanosaurus possessed a keen set of teeth that were well-suited for processing plant material.

This bipedal dinosaur exhibited abbreviated forelimbs and elongated hindlimbs featuring substantial attachments for muscle connection. Its hands were wide and compact, and its fingers were of short length. The creature possessed a diminutive head. Its dentition comprised small, leaf-shaped cheek teeth, characterized by triangular form and minor ridges, with denticles along both the front and rear edges. Additionally, the premaxillary teeth displayed reduced ornamentation.