Scientists have classed a Papua New Guinea frog species much smaller than a US 10-cent coin the world's smallest known vertebrate.
The two types of frog, Paedophryne amauensis and Paedophryne swiftorum, measure seven-point-seven and just over eight millimeters respectively.
The scientist who has identified them as a separate species says the frogs' call is so high-pitched at first he thought it was an insect.
Chris Austin says he had to sort through a bundle of leaf litter to find the tiny amphibians.
"These things are really, really small. In fact they're so small that although you can see the frogs with the naked eye you can't really see very many of the features with the naked eye, such as colour pattern and the number of toes and so forth."
Chris Austin says the biggest challenge for a frog that small is staying moist.
