Proceratosaurus bradleyi is a middle Jurassic member of the tyrannosaur family. The skull was originally discovered about 100 years ago and was only recognized as an early tyrannosaur recently. According to Science Daily, which reports on a paper in the Zoological Journal of the Linnean Society.
According to Science Daily:
The investigations uncovered a wide range of features in the cranial cavity, teeth and jaws that Proceratosaurus shares with the huge T. rex, despite the fact that the Proceratosaurus skull is about 100 million years older and much smaller. The Proceratosaurus cranium was about five times less massive than that of its mighty relative, and the intact animal appears to have weighed only about 40 kg. Mature specimens of Tyrannosaurus, in contrast, weighed in at up to eight tons.
Because the Proceratosaurus skull already displays characteristics that are typical of its later descendants, the powerful jaw with its slicing teeth was probably the animal’s most important weapon. “It is likely that this hunting strategy developed first,” says Rauhut. The basic tool kit was perfected in later tyrannosaurids: The skull became more robust and the jaw muscles larger and, overall, the body increased enormously in size. Proceratosaurus also confirms that the tyrannosauridae developed over a very long stretch of time, and gave rise to a great diversity of forms. Further members of the family surely await discovery.”
The paper can be found here. Additionally, the abstract to a presentation on the same subject is in the Journal of Vertebrate Paleontology 28:130A