Size and Weight:
Unlike its similarly named cousin, Dilophosaurus, Monolophosaurus hasn't quite seized the public's imagination--even though this allosaur (as it has tentatively been classified) was slightly bigger than Dilophosaurus and probably more dangerous. Like all theropods, Monolophosaurus was a meat-eating biped; based on geological clues from where it was discovered, it likely prowled the lakebeds and riversides of late Jurassic Asia.
Why did Monolophosaurus have its single, prominent crest? As with all such dinosaur features, this was likely a sexually selected characteristic--that is, males with bigger crests were more dominant in the pack and could more easily mate with females.