With voices hardly louder than an insect's buzz, the tiniest frogs ever discovered are smaller than a coin and hop about the rainforest of the tropical island of Papua New Guinea, US scientists say.
Not only are Paedophryne amauensis and Paedophryne swiftorum the smallest frogs known to man, they are also the smallest vertebrates, said the report in the science journal PLoS ONE.
The little land frog Paedophryne amauensis comes in at 7.7mm. The Paedophryne swiftorum measures a bit over 8mm.
Previously the smallest vertebrate was believed to be a transparent Indonesian fish known as Paedocypris progenetica, averaging 8mm.
"It was particularly difficult to locate Paedophryne amauensis due to its diminutive size and the males' high pitched insect-like mating call," said Louisiana State University scientist Chris Austin, who discovered them.
"But it's a great find. The ecosystems these extremely small frogs occupy are very similar, primarily inhabiting leaf litter on the floor of tropical rainforest environments," said Austin.
"We believe these creatures aren't just biological oddities, but instead represent a previously undocumented ecological guild - they occupy a habitat niche that no other vertebrate does."
In fact, judging by the frequency of male mating calls they heard, Austin said the tiny frogs might be spaced as close as 50 centimetres from each other on ground beneath the leaves.