Pinacosaurus

Pinacosaurus ("plank lizard") is a genus of medium-sized ankylosaur dinosaurs that lived from the late Santonian to the late Campanian stages of the late Cretaceous Period (roughly 80–75 million years ago), in Mongolia and China. Pinacosaurus had between two and five additional holes near each nostril, which have not been explained.

Description
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.

Discoveries
The American Museum of Natural History sponsored several Central Asiatic Expeditions to the Gobi Desert in Mongolia in the 1920s. Among the many paleontological finds from the "Flaming Cliffs" of the Djadokhta Formation in Shabarakh Usu were the original specimens of Pinacosaurus.[6] The holotype (AMNH 6523) is a partially crushed skull, jaws, and dermal bones collected in 1923.[7]

Pinacosaurus is the best known Asian ankylosaur with more than 15 specimens, including one nearly complete skeleton, five skulls or partial skulls,[8] and two finds of several juveniles huddled together, evidently killed by a sandstorm (Jerzykiewicz, 1993; Burns et al., 2011). The best skull belongs to a juvenile described by Teresa Maryanska in 1971 and 1977.