Rhinella alata Forest Toad
Some other names for this species:
Leaf-litter Toad
The genus Rhinella was split from Bufo by Frost et al in 2006. Some authorities are not at all happy about this.
Pipeline Road, near Gamboa, Panama province, PanamaApril 18, 2001
Forest Toad (Rhinella alata) Forest Toad (Rhinella alata)
These toads have incredible camouflage against the leaf litter throughout which they hop. They make fine photography models, because they trust their camouflage enough to sit completely still for a long time. Both of these are youngsters, only an inch or so long.

The status of the various Rhinella species in this area is still unsettled, and it's not at all certain that R. alata will be around long-term as a taxonomic concept. But this seems like the best match given the current taxonomy on AmphibiaWeb, at least.

Pipeline Road, near Gamboa, Panama province, PanamaJanuary 28, 2016
Forest Toad (Rhinella alata)
When I revisited this road fifteen years later, the abnormally dry weather had left few herps active. We did see a few teeny-tiny toads though.
Online references: