Size and Weight:
"Abel's lizard" (so named because it was discovered by the Argentinian paleontologist Roberto Abel) is known by only a single skull. Although entire dinosaurs have been reconstructed from less, this lack of fossil evidence has forced paleontologists to hazard some guesses about this South American dinosaur. As befitting its theropod lineage, it's believed that Abelisaurus resembled a scaled-down Tyrannosaurus Rex, with fairly short arms and a bipedal gait.
The one odd feature of Abelisaurus (at least, the one that we know of for sure) is the assortment of large holes in its skull, called "fenestrae," above the jaw. It's likely that these evolved to lighten the weight of this dinosaur's massive head, which otherwise might have unbalanced its entire body.