Period: Late Cretaceous
Order, Suborder, Family: Saurischia, Theropoda, Tyrannosauridae
Location: North America (United States)
Length: Estimated 17 feet (5 meters)
Known from only a single skull and jaw from Montana and three teeth from South Dakota, Nanotyrannus was first thought to be an Albertosaurus. But it was recently redescribed because it was different in many ways from Albertosaurus. One difference was that Nanotyrannus had eyes that faced forward. The eyes of Albertosaurus were more on the sides of its head, with little overlap of eyesight at the front. Nanotyrannus could judge distances, sizes, and angles of attack. It probably roamed around in low plants, waiting in ambush, then leaping on its prey. Albertosaurus probably hunted much differently because it could not judge distances.
Nanotyrannus had a curved neck, which gave it more power when it attacked. The back of its skull was expanded for the attachment of muscles from the jaw and neck, which increased the sideways motion of its neck and head. It stood about seven or eight feet tall at the shoulder and probably weighed about one ton.
The teeth of Nanotyrannus were not well preserved, but they were serrated blades like most meat-eating dinosaurs. Many parts of the skull of Nanotyrannus are puzzling; some of the bones were not fused (joined). This may mean that it was not an adult; some paleontologists think it could have been a juvenile Tyrannosaurus. Tyrannosaurus, which has been found in the same deposits, also had eyes that faced forward. Also, a number of skulls of Tarbosaurus, a close relative of Tyrannosaurus, were found in Mongolia. The smallest and probably the youngest looks much like Nanotyrannus. Further study may prove that Nanotyrannus was a juvenile Tyrannosaurus.