Size and Weight:
One of the earliest tyrannosaurs yet to be discovered, Guanlong (the name, "crown dragon," alludes to this meat-eater's prominent crest) roamed eastern Asia during the late Jurassic period. Like other early theropods--such as Eoraptor and Dilong--Guanlong was nothing special in terms of size, only a fraction as large as Tyrannosaurus Rex (which lived about 90 million years later). This points to a common theme in evolution, the development of plus-sized animals from small progenitors.How do paleontologists know that Guanlong was a tyrannosaur? Clearly, this dinosaur's crest--not to mention its fairly long arms and (possibly) its coat of feathers--make it an ill-fitting match with the classic tyrannosaurs of the late Cretaceous period. The giveaway is the characteristic shape of Guanlong's teeth and pelvis, which point to its being a "basal" (i.e., early) member of the tyrannosaur family. Guanlong itself appears to have descended from earlier, smaller theropods known as coelurosaurs, the most prominent genus of which was Coelurus.
Oddly, when Guanlong was discovered, in China's Shishugou formation, the paleontologists from George Washington University found two specimens lying on top of one another--one surmised to be about 12 years old, and the other about 7. What's weird is that, as far as researchers can tell, the dinosaurs didn’t die at the same time, and there's no sign of a struggle--so how did they wind up buried together? It's still a tantalizing paleontological mystery.