Wannanosaurus (meaning "Wannan lizard", named after the location where it was discovered) is a genus of basal pachycephalosaurian dinosaur from the Maastrichtian Upper Cretaceous Xiaoyan Formation, about 70 million years ago in what is now Anhui, China.

Because it has a flat skull roof with large openings, it has been considered primitive among pachycephalosaurs.

[2][3] Sometimes it has been classified as a member of the now-deprecated family Homalocephalidae,[4][5] now thought to be an unnatural assembly of pachycephalosaurians without domed skulls.

[3] Although its remains are from a very small individual, with a femur length of ~8 centimeters (3.1 in) and an estimated overall length of about 60 cm (2 ft),[2][6] the fused bones in its skull suggest that it was an adult at death.

[7] Like other pachycephalosaurians, it was probably herbivorous or omnivorous, feeding close to the ground on a variety of plant matter, and possibly insects as well.