Discovered by Charles Darwin in the thick, gloomy forests of southern-central Chile, Darwin's frog (Rhinoderma darwinii) possesses a distinctive appearance and an unusual biology. The head of this species has a triangular appearance due to the presence of a pronounced, fleshy proboscis that projects from the tip of the snout. The colouration of the warty upperparts is variable, with individuals exhibiting various shades of brown, green or a mixture of the two. By contrast the underparts are invariably black and white with large blotches. The male Darwin's frog possesses a large vocal sac, extending from beneath the throat, over the belly, to the groin. Rather than enabling the male to produce a booming call, this sac has an unusual role in brooding offspring, and the call is, in fact, small and bell-like.