Pinacosaurus

***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.

*Pinacosaurus* was a lightly built, medium-sized animal, fully grown individuals reached a total length of 5 m (16 ft).[1][16] Gregory S. Paul estimated their weight about 1.9 t (4,200 lb),[14] Thomas R. Holtz however, estimated it between 454 to 907 kg (1,001 to 2,000 lb).[16] The postcranial skeleton PIN 614 measures 3.66 m (366 cm) from the first neck vertebrae to the end of the tail.[6]

In 2014, Arbour established some distinguishing traits of the genus. The upper snout armour does not consist of distinct tiles, *caputegulae*, but of a fused mass. Adult individuals have a skull that is longer than wide. This trait is shared with the distant relatives *Gobisaurus* and *Shamosaurus*, but *Pinacosaurus* differs from those in the possession of extra openings in the nostril and a pointy protruding *caputegula* on the prefrontal, directed to the front. *Pinacosaurus* differs from *Crichtonpelta* in the lack of an ornamented rear edge of the skull roof and in the cheek horn not being curved upwards.[12]

Size compared to an average human male

Arbour also provided a list of traits in which *P. grangeri* and *P. mephistocephalus* differed from each other. *P. grangeri* has a notch in the snout armour just above the innermost nostril opening. *P. mephistocephalus* has squamosal horns extending to behind beyond the rear of the skull roof, their points representing the widest point of the skull, instead of the upper rims of the eye sockets. *P. mephistocephalus* also has a clear transverse narrowing of the skull roof at level of the lacrimals, just in front of the eye sockets. It had been suggested that the rear skull roof of *P. mephistocephalus* was more convex but Arbour concluded it essentially had the same curvature.[12] The holotype of *P. mephistocephalus* has very long cheek horns but a juvenile specimen, MPC 100/1344, found as part of a *P. grangeri* group, shows a similar elongation.[4]