These are impressively large treefrogs. They earned the name "Gladiator Treefrogs" because the adult males use exposed bones on their thumbs to do battle for territory. This one was, however, just sleeping peacefully on a leaf.

Here is a complete list of the herps I saw in the wild on my 2013 MT Amazon Expeditions trip.

These two very large adult Boana boans guarded different edges of a good-sized pond just off the Nauta road, which also featured another large treefrog species, as well as a friendly caiman.