Pinacosaurus was a lightly built, medium-sized ankylosaur that reached a length of 5 meters (16 ft)[2] Like all ankylosaurids, it had a bony club at the end of its tail which it used as a defensive weapon against predators such as Velociraptor. The most unusual element in the original specimen is the presence of two additional egg-shaped holes, one on top of the other, where the nostrils are normally found.[3] The openings are characteristic of the genus, and the number varies: Godefroit et al. described four in 1999, and in 2003 a juvenile specimen with of five pairs of openings was described.[4] Its forelimb has five digits, and the phalangeal formula is 2-3-3-3-2, meaning that the innermost finger of the forelimb has two bones, the next has three, etc.