Size and Weight:
The rare ornithomimid ("bird mimic") Anserimimus is known only from a single, incomplete skeleton found in the Gobi Desert--including a hindlimb and a forelimb but (as is often the case with dinosaurs) no head. Like other ornithomimids of the late Cretaceous period, Anserimimus probably had no teeth and subsisted on small insects, reptiles and mammals, though its atypically powerful arms may be a hint that it occasionally pursued larger prey.
By the way, unlike Struthiomimus ("ostrich mimic") and Gallimimus ("chicken mimic"), Anserimimus probably didn't look much like a goose, after which it's named. That's because the paleontologist who first described it wanted to follow the ornithomimid tradition of naming new genera after existing birds.