From the San Diego Natural History Museum, here’s a cut-away Albertosaurus:
The various subspecies of Albertosaurus look a bit like Tyrannosaurs, and they’re related — but dramatically smaller (about a third the mass of a T-rex). So you can think of them as the “sport model” of the T-rex.
Named after the Canadian province where the first of their fossils were found, Albertosaurs roamed the earth some 8 million years before the Tyrannosaurs. The first specimen (a partial skull) was found in 1884, but since then the remains of more than 30 individuals have been found. 22 of them were found at a single site, indicating that they lived (or at least hunted) in packs.