Tropidurus torquatus Amazon Lava Lizard
Some other names for this species:
Eastern Collared Spiny Lizard
Iguaçu National Park, Paraná, BrazilNovember 7, 2006
Amazon Lava Lizard (Tropidurus torquatus) Amazon Lava Lizard (Tropidurus torquatus) Amazon Lava Lizard (Tropidurus torquatus)
These lizards were common around Iguaçu 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. torquatus, since that seems to be the only species mentioned from this location on the web.

Online references: