All the new species belong to the genus Nyctibatrachus, scientists said. Frogs of this genus are commonly known as night frogs because of their dark colors and habitats.
The amphibians were found over the course of five years by University of Delhi scientists who went on extensive expeditions through India's Western Ghats region, an amphibian and global biodiversity hot spot.
The four new miniature species are among the smallest known frogs in the world.
The tiny frogs are as small as 12 mm (less than half an inch), and they grow no bigger than 16 mm, according to researchers. They can sit comfortably on a coin or fingernail.
Scientists said they were surprised that the miniature frogs were locally abundant, according to Sonali Garg, a University of Delhi student who participated in the expeditions as part of her Ph.D. research.
The tiny frogs species were likely overlooked by researchers "because of their extremely small size, secretive habitats and insectlike calls," she said.
Unfortunately, the future for many of the new species may be bleak, according to scientists.
Many of the frogs live outside protected areas and on human-altered properties, researchers said. Those frogs face threats such as habitat disturbance, modification and fragmentation.
"Over 32 percent — that is one-third of the Western Ghats frogs — are already threatened with extinction," said S.D. Biju, a University of Delhi professor who led the study.
Biju has formally described more than 80 new species of amphibians from India over the course of his career.
"Out of the seven new species, five are facing considerable anthropogenic threats and require immediate conservation prioritization", he said.
More details about the frogs can be found in the study published today in PeerJ.