Since the tyrant lizards have been in the news so much lately, I figured I'd write a bit on our best known of the early tyrannosaurs, a beast discovered in Late Jurassic rock in China and named Guanlong. The other Jurassic tyrannosaurs are not nearly as well known. We have two relatively complete Guanlong specimens, an adult and a juvenile. While many tyrannosaurs feature head ornamentation of some sort - bumps, spikes, or small crests, Guanlong's head bore a large, delicate crest which in profile looks somewhat like that of Dilophosaurus.
Like the early Cretaceous Chinese tyrannosaur Dilong, it's likely that Guanlong was covered, at least partially, in hairy "proto-feathers." These would have been for warmth and display purposes, and the later giants of the family show no evidence of them, and would not have needed them to maintain their temperature as their large size would have done that job just fine. Both Guanlong and Dilong had three fingers; recently described Raptorex is the earliest tyrannosaur to bear the distinctive two-fingered hand.
National Geographic published a nice article on Guanlong in July of 2008, and the site also features a gallery dedicated to the fossilized mud trap where Guanlong was discovered with a whole mess of tasty fossils.
Drawing by Renato Santos.