Size and Weight:
About Tyrannosaurus Rex:
Tyrannosaurus Rex is by far the most popular of all dinosaurs, spawning a huge number of books, movies, TV shows and video games. What's truly amazing, though, is how much about this carnivore that was once assumed as fact has lately been called into question. (See a gallery of Tyrannosaurus Rex pictures and 10 Facts About T. Rex.)
For example, one controversy that's currently making the rounds among paleontologists is whether T. Rex was a hunter or scavenger. Some experts think T. Rex feasted on already dead prey, on the premise that it couldn't have been fast enough or smart enough to hunt down other dinosaurs--but it was equipped with features (such as a superior sense of smell) that are found in modern scavengers, like vultures. In another development, it's now believed that T. Rex individuals may have succumbed to trichomonosis, a parasitic disease that affects modern birds, and it's entirely possible that T. Rex juveniles were covered in downy coats of feathers, at least to judge by another genus of tyrannosaur, the Asian Dilong.
Despite how it's depicted in action movies, we don't know for sure how speedy Tyrannosaurus Rex was. Unlike the juggernaut of the Jurassic Park movies, it's possible that this dinosaur lumbered along at a poky 10 miles per hour, max--meaning a hungry female would have found it hard to outrun a kid on a bicycle! (For the record, other theropods of the late Cretaceous period, notably the ornithomimids, were capable of sprinting at a zippy 50 miles per hour or so.) New research, which implies that T. Rex adults may have tipped the scales at 10 tons, also places some limits on how fast this dinosaur could have run! Its arms were still tiny, though, a puzzling fact that's explained in the article Why Did T. Rex Have Such Tiny Arms?
T. Rex coexisted with another famous dinosaur, Triceratops--and it's not inconceivable that these two dinosaurs occasionally tangled it up. See Tyrannosaurus Rex vs. Triceratops - Who Wins? for an analysis of this epic battle.