These lizards were common around Iguazú National Park. The first one I saw was the handsome tree-hugging adult pictured above. Most of the others I saw were on rocks, which befits their "Lava Lizard" name. The second photo here is a juvenile on a mossy forest rock. The third photo shows one of several lizards that were hanging out on partly-submerged boulders with crashing waterfalls only a few yards away.

I'm pretty sure that these three are all the same species. I'm quite confident that they are Tropidurus, and I think the species is T. etheridgei, but I haven't found enough information on that species to be completely certain. I've found dozens of websites that mention the common Tropidurus lizards at Iguazú, but precious few that dare mention a specific name. Please let me know if you have any further information.