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Tyrannosaurs are a group of predatory dinosaurs that includes the famous Tyrannosaurus. Initially thought to belong to the carnosaurs due to their size and similar characteristics, more evidence shows a closer affinity to the coelurosaurs and birds than to the carnosaurs. The oldest known tyrannosauroid would be Proceratosaurus and Kileskus in the Middle Jurassic, but it is known from a few fragments. The more complete Guanlong (placed here in the family Proceratosauridae) dates back to the Late Jurassic. A majority of tyrannosaurs have been found in the Cretaceous. According to the remains of Guanlong, Dilong, and Eotyrannus; early tyrannosaurs were built not unlike other typical coelurosaurs with long legs and arms ended with three-fingered hands. But over time, the number of fingers reduced to two. The head grew bigger and the arms grew smaller. Towards the end of the Cretaceous, the change of the ratio between the lower and upper leg bones to becoming equal betrays a tendency to become slower.

Tyrannosaurs are united by many characteristics. Among them, they have a single nasal bone that fused early in the animal's life. They also have unique pelvises, which is why two dinosaurs known from parts of a pelvis, like Stokesosaurus and Aviatyrannus from the Late Jurassic, are considered possible tyrannosaurs.

Tyrannosaurs have been found in Asia, North America, and Europe. But recently in 2010, scientists rediscovered a fossil that they claimed belonged to a tyrannosaur from Dinosaur Cove, Australia. If true, then the tyrannosaurs must have populated parts of the Southern Hemisphere as well.

Classification:

        • Tyrannosauroidea
          • Family Proceratosauridae
          • Family Tyrannosauridae

Resources:

Smith, Bridie "Tyrannosaur dinosaurs called Australia home," 26 Mar 2010

"DinoData - Tyrannosauria"

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