Size and Weight:
As carnivorous dinosaurs go, Albertosaurus is fairly well known, with multiple, more-or-less complete fossils of this famous tyrannosaur having been dug up in North America (many in the Canadian province of Alberta, after which the genus is named). Unfortunately, it seems to be Albertosaurus' fate to forever be considered a lesser cousin of the slightly bigger Tyrannosaurus Rex, which was discovered around the same time (in fact, Albertosaurus was mentioned as a mere "footnote" at the end of one famous T. Rex paper penned by Henry Fairfield Osborn.)
Albertosaurus "only" weighed about two or three tons (compared to more than twice that for the largest T. Rex individuals), but this meat-eater was every bit as dangerous--and, considering its more petite size, possibly faster and nimbler in the pursuit of prey. This tyrannosaur made its living by hunting the numerous herbivorous dinosaurs of the late Cretaceous period, probably making a specialty out of slow-witted hadrosaurs, or duck-billed dinosaurs.
Scarily, paleontologists have found (admittedly inconclusive) evidence that Albertosaurus may have hunted in packs. If this is the case, then not even the armored, full-grown plant eaters of late Cretaceous North America (such as Triceratops) would have been truly safe from being turned into a quick lunch. (By the way, some paleontologists insist that the fearsomely named tyrannosaur Gorgosaurus should properly be classified as a species of Albertosaurus, though not all experts agree.)