Not sure about a dewlap. The throat muscles attach all the way at the front of the jaws, and the hyoid bones lie along these muscles and parallel to the mandibles, as recovered in multiple specimens in which no distinct dewlap is present, at least a muscular one. Expansive throat pouches and extensible dewlaps, a la anoles, have particularly unique hyoid bones and we don't have data supporting such a thing in almost any dinosaur. I say almost any. There are some dinosaurs that suggest some unique throat muscles, but for the most part these are not included in cranial reconstructions and their presence is only slightly hinted at when studying their heads. I won't get into that right now.