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Paedophryne amauensis is a leaf-litter frog from eastern Papua New Guinea, described in 2012 from specimens collected near Amau Village, Central Province. At its description it was, by snout-to-vent length, the smallest known vertebrate species — smaller than any other frog, fish or amniote measured up to that point. Its size and cryptic habits make it one of the harder amphibians to find in the field: most individuals are located by ear rather than by sight.
Identification
Adults are tiny even among miniaturised frogs, averaging about 7.7 mm in snout-to-vent length, with the type series ranging roughly 7.0–8.0 mm. The Guinness World Records entry lists a body mass around 10 mg. The dorsal surface is dark brown with irregular tan to rusty-brown blotches, and the sides and underside are dark brown to slate grey. The body plan is otherwise ordinary for the genus: moderately long legs, a broad short snout and relatively large eyes, with unwebbed digits carrying slightly enlarged discs, and the first finger and toe reduced to vestigial nubs. Extreme miniaturisation has also simplified the skeleton: the species has only seven presacral vertebrae, fewer than most frogs. Despite its size it is an able jumper, reportedly capable of jumps up to thirty times its body length.
Habitat and range
The species is endemic to eastern Papua New Guinea, known from the type locality near Amau Village in Central Province and from a further record at Varirata National Park in National Capital District. It lives in leaf litter on the floor of tropical wet lowland and hill forest, from about 177 to 800 m above sea level — the type locality itself sits at the lower end of that range, and the upper bound comes from the Varirata record. A body this small loses moisture quickly, so the frog stays within the constant humidity of the leaf litter rather than venturing into open or drier ground.
Behaviour and breeding
Paedophryne amauensis is crepuscular, calling from within the leaf litter at dawn and dusk. The call is a series of high-pitched, insect-like peeps around 8,400–9,400 Hz, delivered at roughly 1.5 notes per second — a frequency so high, and so easily mistaken for an insect, that it likely kept the species undetected until targeted night surveys of the leaf litter picked it out by ear. Diet is presumed to be small invertebrates such as mites and springtails, in line with its size and forest-floor habitat. Like other extremely miniaturised frogs, it has no free-living tadpole stage: eggs hatch directly into “hoppers,” miniature versions of the adult, skipping the aquatic larval phase that most frogs depend on.
Conservation
The IUCN category is shown in the facts box above. Paedophryne amauensis was only described in 2012 and much of its range lies within intact forest that has not been intensively surveyed, so its status could change as more is learned about its distribution and any threats to its habitat.
Similar species
Paedophryne amauensis shares its genus with several other extremely small New Guinea frogs, including Paedophryne swiftorum, described in the same 2012 paper at 8.25–8.90 mm, as well as P. kathismaphlox and P. oyatabu. Before P. amauensis was described, the smallest known vertebrate on record was an aquatic fish, Paedocypris progenetica, at 7.9–10.3 mm, and the smallest known amniote was a gecko, Sphaerodactylus ariasae, at 16.3 mm. Within the leaf litter of Papua New Guinea, size alone is usually enough to rule out confusion with any frog outside the genus Paedophryne; separating P. amauensis from its closest relatives in the genus depends on precise measurement and call frequency rather than anything visible in the field.