African clawed frog
In 1998, Provencio discovered melanopsin as a novel opsin in the photosensitive skin melanophores of the African clawed frog. In 2000, he showed that melanopsin is also present in mouse, rhesus macaques, and humans, where it is only present in the eye. The unique inner retinal localization of melanopsin indicated that melanopsin was not involved in image formation. Later, he demonstrated that the melanopsin pigment might be involved in entrainment of a circadian oscillator to light cycles in mammals.