Description
Paedophryne amauensis is a very small frog that is one of the world’s smallest terrestrial vertebrate with a male snout-vent range of 7.0 - 8.0 mm. The female snout-vent range is currently unknown as only males have been found. The head is wider than long. It has a broad and short snout. Its eyes are relative large. The fingers are unwebbed and end in slightly expanded discs. The first, second, and fourth fingers are greatly reduced, especially the first, which is vestigial. The phalangeal formula for the hands is 1 – 2 - 3 – 2. The frog has moderately long legs with a tibia to snout-vent length ratio ranging from 0.478 - 0.507. It has unwebbed feet and slightly enlarged discs. The first toe is reduced to a vestigial nub and the second and fifth toes are also notably reduced. The number of phalanges in the foot is 1 – 2 – 3 – 4 – 2. The species only has seven presacral vertebrae (Rittmeyer et al. 2012).

From other species outside of the genus, P. amanuensis can be differentiated by having fewer pre-sacral vertebrate (7 instead of 8). Like other miniaturized species, P. amanuensis also has reduced ossification of some cranial elements and reduction in phalangeal and digital structures of the hands and feet. Paedophryne amanuensis is morphologically distinguished from other members of the genus, P. kathismalphlox, P. oyatabu and P. swiftorum, through its extremely small snout-vent length of 7.0 - 8.0 mm and its moderately long legs with a tibia length to snout-vent length ratio ranging from 0.478 - 0.507. It is distinguished further from P. oyatabu and P. swiftorum by having a longer, narrower head, and from P. kathismaphlox by having a broader, shorter head. Lastly, P. amauensis can be further differentiated from P. swiftorum through its higher dominant frequency call ranging from approximately 8400 - 9400 HZ and consists of single notes rather than eight paired notes (Rittmeyer et al. 2012).

The dorsal side of P. amanuensis is dark brown with some tan to rusty-brown blotches. The lateral and ventral surface of the frog is ranges from dark brown to slate grey with irregular bluish-white speckles (Rittmeyer et al. 2012).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Papua New Guinea

View distribution map in BerkeleyMapper.

Paedophryne amauensis was discovered in leaf litter in wet-tropical primary forests near Amau Village in the Central Province of Papua New Guinea (Rittmeyer et al. 2012).

Life History, Abundance, Activity, and Special Behaviors
These frogs are crepuscular and terrestrial. Like most miniaturized frogs, P. amanuensis inhabits tropical wet-forest leaf litter to compensate for their sensitivity to water loss. They are also assumed to reproduce via direct development. However, as only males have been observed, details on their reproductive behavior is unknown. In general, miniaturized frogs typically produce fewer, large eggs compared to their congeners (Rittmeyer et al. 2012).

These frogs can be primarily heard calling at dawn and dusk from the leaf litter of primary forests. Their calls consists of a continuous series of high-pitched notes that last from 2 - 14 ms, are produced at a rate of 1.5 notes per second, and have a dominant frequency ranging from 8400 - 9400 Hz. The calls last for 1 – 3 minutes with a brief rest of 3.3 – 40.8 seconds before starting again. One male produced 355 calls in four groups over 5.5 minutes. These calls sound similarly to those created from a stridulating insect (Rittmeyer et al. 2012).

Paedophryne amanuensis feed on minute invertebrate species, such as acarians and collembolans. Because of their small size and relatively common abundance, P. amanuensis are likely an important member of the tropical wet-forest ecosystems (Rittmeyer et al. 2012)

As a small species, P. amanuensis is likely more susceptible to invertebrate predation, which may may explain its absence from aquatic habitats and tendency to inhabit upland habitat where there is less invertebrate diversity than the lowlands (Rittmeyer et al. 2012).

Comments
Based on Maximum Likelihood analysis of 12S and 16S ribosomal RNA gene, P. amanuensis is sister to P. swiftorum. However, there are deep divergences between Padeophyrne species, with uncorrected p-distances of greater or equal to 0.102, suggesting that the small size of the genus arose from early radiation of microhylid frogs in New Guinea. Genetic analysis also suggests that the genus Paedophryne has a close relationship with Barygenys exsul and Cophixalus balbus (Rittmeyer et al. 2012).

Paedophryne amauensis took the title for the world’s smallest vertebrate from Paedocypris progenetica, an Indonesian fish that measures at 7.9 mm (Rittmeyer et al. 2012).

The ecological similarities of the genus Paedophyrne suggests an independent origin of minute frogs that adds evidence to an ecological niche that miniaturized frogs occupies rather than their being evolutionary outliers (Rittmeyer et al. 2012).

The discovery of P. amauensis, along with its sister species P. swiftorum expands the range of the genus Paedophyrne westward (Rittmeyer et al. 2012).

This species was featured in News of the Week 18 November 2024:

What is the smallest vertebrate (animals with a backbone) in the world? Turns out, it’s a frog. Bolaños et al. (2024) compared measurements of many miniature frog species and found that even though there are lots of very small frogs, the Brazilian Flea Toad, Brachycephalus pulex, are the amphibians with the smallest total length recorded, thus taking the title of the tiniest anuran amphibian. And it was a close call, as the flea-toad beat out Paedophryne amauensis by less than a mm! The tiniest vertebrate invokes questions about their biology, and Carrasco-Medina et al. (2023) investigated whether such small body sizes might affect the cardiorespiratory system, specifically the lungs and heart. They compared closely related frog species (mostly Brachycephalus) and found the species with the smallest body sizes had reduced features in both the heart and lungs and very thin skin. As a result, the authors suggest that these extremely small species likely rely more on their skin than their lungs to bring in oxygen. (Written by Molly Womack)

References

Rittmeyer, E. N., Alison, A., Grüdler, M. C., Thompson, D. K., Austin, C. C. (2012). ''Ecological guild evolution and the discovery of the world’s smallest vertebrate.'' PLoS ONE, 7(1), e29797. [link]

Species Account Citation: AmphibiaWeb 2024 Paedophryne amauensis: New Guinea Amau Frog <https://amphibiaweb.org/species/7760> University of California, Berkeley, CA, USA. Accessed Nov 21, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 21 Nov 2024.

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