Osteocephalus yasuni — Yasuni Broad-headed Treefrog
This species was described in 1999. Prior to that, specimens were considered O. planiceps or O. lepreurii.
These are big, bold treefrogs, always ready to leap away an instant before you got the shot. The various Osteocephalus species can be tricky to tell apart, but yellow on the underside is a diagnostic characteristic of O. yasuni.
This large treefrog is clearly an Osteocephalus, but I am not certain of the species. Due to the small tympanum, reticulations rather than radiating lines in the iris, and white supralabial area, I suspect it is O. yasuni, though it has no apparent yellow, unlike most or all of the other O. yasuni that I've identified.
Here's a more typical-looking individual, showing the yellow belly. It is in the traditional "I am about to jump really far away from you" position.
I'm reasonably confident that the first two yellowish frogs here are Osteocephalus yasuni. I'm less confident about the third one. The eyes and tympanum seem to match O. yasuni, but there's no sign of the normal yellow color. Any thoughts?
I initially thought this frog was Osteocephalus leprieurii due to the lack of yellow and some other details. But in my online Osteocephalus-identification research, I came across an overview of the systematics of this group from 2015, which explained that O. leprieurii is no longer considered to live in this area. The frogs formerly considered to be that species are now included in O. yasuni.