A few days ago we were walking down by the plaza and noticed a local looking up into the trees. We followed his gaze and discovered several huge iguanas lounging in the afternoon sunshine. He came over to us and pointed out many more iguanas. There were at least 30 in one tree and a few of them were almost 6' long. Two of those really big ones were displaying aggressive behavior towards one another; head bobbing, open mouths, lunging at each other. Finally one of them lunged too far and fell out of the tree. He didn't seem hurt and scrambled back up where his competitor was to continue the contest.
The photo above is one of the medium sized ones; only about 4' long. The video below is of him enjoying his lunch of mesquite leaves.