Pinacosaurus (meaning "Plank lizard") is a genus of ankylosaurid thyreophoran dinosaur that lived in Asia during the Late Cretaceous (Santonian-Campanian, roughly 80 million to 75 million years ago), mainly in Mongolia and China. The first remains of the genus were found in 1923, and the type species Pinacosaurus grangeri was named in 1933. Pinacosaurus mephistocephalus named in 1999, is a second possibly valid species differing from the type species in details of the skull armour. Of Pinacosaurus grangeri many skeletons have been found, more than of any other ankylosaur. These predominantly consist of juveniles that perhaps lived in herds roaming the desert landscape of their habitat. Pinacosaurus was a medium-sized ankylosaurine, about five metres long and weighed up to two tonnes. Its body was flat and low-slung but not as heavily built as in some other members of the Ankylosaurinae. The head was protected by bone tiles, hence its name. Each nostril was formed as a large depression pierced by between three and five smaller holes, the purpose of which is uncertain. A smooth beak bit off low-growing plants that were sliced by rows of small teeth and then swallowed to be processed by the enormous hind gut. Neck, back and tail were protected by an armour of keeled osteoderms. The animal could also actively defend itself by means of a tail club.