Hyloscirtus tolkieni, commonly known as the Río Negro stream frog, is a species of frog in the family Hylidae. It is endemic to the Andes Mountains in Ecuador, where it has been observed at 3190 meters above sea level. The adult female frog measures 64.9 mm in snout-vent length. It is gray-green in color with yellow and black marks. The iris of the eye is pink with a black rim. There are yellow and black spots on the belly and flanks. It has some fringed skin on the front and back toes. These frogs live in riparian habitats. The tadpoles live in cracks in the rocks underwater. The adult frogs appear nocturnal animals. Scientists have seen them on high tree branches not far from the water. The scientists who published the first description of this species named this frog after author J.R.R. Tolkien. They paraphrase The Hobbit in the introduction to their paper. References Frogs of South America Endemic fauna of Ecuador Amphibians described in 2023 tolkieni