Just say the word "tyrannosaur," and most people immediately picture the king of all dinosaurs, Tyrannosaurus Rex. However, as any paleontologist worth his pickaxe will tell you, T. Rex was far from the only tyrannosaur roaming the forests, plains, and swamplands of the Cretaceous period (although it was certainly one of the biggest). From the perspective of a small, quivering herbivorous dinosaur, Daspletosaurus, Alioramus, and a dozen or so other tyrannosaur genera were every bit as dangerous, and their teeth were just as sharp.
As with other broad classifications of dinosaurs, the definition of a tyrannosaur (Greek for "tyrant lizard") involves a combination of arcane anatomical features and broad swathes of physiology. Generally speaking, though, tyrannosaurs are best described as large, bipedal, meat- eating theropod dinosaurs possessing powerful legs and torsos; large, heavy heads studded with numerous sharp teeth; and tiny, almost vestigial-looking arms. As a general rule, tyrannosaurs tended to resemble one another more closely than did the members of other dinosaur families (such as ceratopsians), but there are some exceptions, as noted below. (By the way, tyrannosaurs weren't the only theropod dinosaurs of the Cretaceous period; other members of this populous breed included raptors, ornithomimids and feathered "dino-birds.")