In 2011, scientists discovered the flea toad, or Brachycephalus pulex, in Brazil and may have found the world’s smallest vertebrate. This tiny amphibian was seen perched on a Brazilian real coin, which has a diameter of 27 millimeters. The frog is smaller than the previous record holder for the world’s smallest vertebrate.
Although flea toads are known for their small size, only a limited number of specimens have been collected from their habitat on forested hilltops in southern Bahia, Brazil. In order to verify the species’ maturity and sex, scientists examined the gonads of the frogs. Only males were found to have vocal slits.
Adult male B. pulex frogs are slightly over 7 millimeters long, smaller than females, making them even smaller than the previously known smallest amphibian, the Paedophryne amauensis frog from Papua New Guinea. The findings suggest that flea toads may be the smallest extant frog in the world.
The study also revealed that flea toads can get much smaller than other mini frogs at such small scales. The smallest specimen in the study was only 6.45 millimeters long. At such scales, frogs develop unusual anatomical quirks such as losing toes or having underdeveloped ears.
Researchers also suggested that there may be even smaller vertebrates yet to be discovered, leading to the possibility of the next record-holder being another small frog or perhaps a parasitic male of a deep-sea anglerfish.