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 â `` 75 million years ago ) , in Mongolia and China . 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 .