Trilophosaurs were lizard-like Triassic diapsid reptiles related to the archosaurs. The best known genus is Trilophosaurus, a herbivore up to 2.5 meters long. It had a short, unusually heavily-built skull, equipped with massive, broad flattened cheek teeth with sharp shearing surfaces for cutting up tough plant material. Teeth are absent from the premaxilla and front of the lower jaw, which in life were probably equipped with a horny beak. The skull is also unusual in that the lower temporal opening is missing, giving the appearance of a euryapsid skull, and originally the Trilophosaurs were classified with placodonts and sauropterygia. Carroll 1988 suggests that the lower opening may have been lost to strengthen the skull.