Monolophosaurus was one of the first known members of the family Tetanurae, common ancestors of Allosaurids, Megalosaurids, Spinosaurids and Coelurosaurs (which includes raptors and tyrannosaurs!). Evolving from smaller predatory theropods like Coelophysis and Liliensternus, Monolophosaurus was approximately 18 feet long and built as a strong runner with a tough skull. The "crest" is more of a central ridge running down the front midline of the skull, more than likely too low to have shown from under the facial muscles, skin and scales. The crest would have enlarged the sinus cavities and lightened the skull, giving both a more pronounced sense of smell, more attachment space for jaw muscles, and possibly sinus adaptations for dry environments. A big hunter cannot afford to lose water through breathing and become dehydrated mid-hunt in the early Jurassic scrub!

This guy is just trotting along, casting about for scents and keeping a wary eye out for larger predators (crocodylomorphs--back in the days before large theropods, land-based crocs and dinosaur-like reptilian ancestors would have still been apex predators over the more lightly-built theropods).