Two small frogs found in southeastern New Guinea are said to be the world's smallest, measuring about 0.4 inches or 8 to 9 millimeters in length. They belong to a group that has small fingers and so they are not expert climbers.

Instead, the frogs, which are smaller than a penny, are excellent leaf litter dwellers.

The two species, Paedophryne dekot and Paedophryne verrucosa, are also the world's smallest tetrapods. Tetrapods are four-limbed animals that have backbones. They include amphibians, reptiles and mammals to name a few.

The two frog species were discovered through field work from researcher Fred Kraus from Bishop Museum in Honolulu, HI. The study was published in the journal ZooKeys.

Miniaturization occurs in many frog genera around the world but New Guinea seems particularly well represented, with species in seven genera exhibiting the phenomenon, Kraus said in a press release. Although most frog genera have only a few diminutive representatives mixed among larger relatives, Paedophryne is unique in that all species are minute.

Kraus discovered the Paedophryne in 2002 from previous research. However, it wasn't formally described until last year. Those species first described were slightly larger, as they grew to a size of 10 to 11 millimeters.

The four known species all live in small ranges in the mountains of southeastern New Guinea or next to offshore islands, according to researchers.

It is unclear who their closest relatives are.

Photographs issued show that the frogs are red-brown in color, with brown and black-looking triangles just above their sides. Some have lumps-like things on their skin with yellow blemishes.

Along with their small body sizes the frogs have tiny fingers and toes, which doesn't allow them to climb very well and so they live on forest floors, inhabiting leaf litters and moss.

Researchers said that living in leaf litter and moss is common among miniaturized frogs and may reflect their exploitation of novel food sources in that habitat.

A press release on the discovery noted that because of the frogs' small body sizes females carry only two eggs. Researchers don't know if both eggs are laid simultaneously or at different intervals.