Description
Silverstoneia minutissima is a small forest-dwelling frog with an adult snout-vent length of 13.3 - 16.2 mm for males and 14.5 - 17.0 mm for females. The head width is 31% - 38% of the snout-vent length, slightly wider than the diagonal head length. In the dorsal view, the nostrils are flared, and the snout is narrowly rounded. The nostrils are located closer to the snout than to the eyes, while the distance between upper eyelids are smaller than the snout length. The canthus rostralis is round. The loreal region can be either slightly concave or flat, while being vertical or slightly outwardly-sloped. The eyes are large, like other members of the same genus, taking up 40% - 49% of head length. Numerous specimens have externally indistinct tympanum, possibly a result of preservation. A distinguishable supratympanic ridge or fold is absent, maxillary teeth are present. The skin appears mostly smooth while the posterior dorsum, shank, and eyelid can be slightly granular. The hands are longer than the forearms. Protruding, elliptical thenar tubercles and less protruding, triangular palmar tubercles are present on the hands. No metacarpal fold is present on the palm. When appressed and flattened, the relative lengths of fingers are III > I > II ≈ IV. No distinct lateral fringes are present on fingers. Pads on each finger are slightly expanded, and small scutes are present on the dorsal side of each digit. The foot length is shorter than that of the tibia, but is 1.5 - 2.4 times of the hand length. Feet tuberculation includes the smaller, more protruding round, outer metatarsal tubercle and the less protruding, elliptical inner metatarsal tubercle. When appressed and flattened, the relative lengths of toes are IV > III > V > II > I. Basal webbing is present between toes III and IV, and weakly present between toes II and III in several specimens. Similar to forelimb fingers, the toe pads are slightly expanded, and small scutes are present on the dorsal side of each digit (Grant and Myers 2013).

Silverstoneia minutissima is highly similar to other members of the genus in terms of physical appearance. However, this species lacks the swollen third fingers in adult males that are usually present in other Silverstoneia species. Additionally, S. minutissima is also has the smallest average snout-vent length for a species than others in the genus. Slivertoneia minima is most similar to S. minutissima. Both species lack conspicuous dark blotches on the ventral side and the swollen third fingers in adult males. In comparison, S. minutissima has paler thighs while S. minima has more darkish pigmentation present dorsally. Silvertoneia minutissima is also smaller than S. minima (Grant and Myers 2013).

In life, the dorsal surface is dark brown. The solid blackish-brown flank is divided by a creamy greenish oblique lateral stripe, extending from the groin to the eye. The throat, breast, and belly have a similar creamy whitish color with a green tinge. The limbs are dorsally light brown and ventrally whitish orange. Tiny, dull orange spots are also present on the dorsal side of the thighs. Preserved specimens are mostly dorsally brown, while random darker or lighter blotches are present. A diffused stripe caused by the underlying vertebral column can be visible through the skin. The eyelids appear blackish (Grant and Myers 2013).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Colombia

View distribution map in BerkeleyMapper.

The species is endemic to Colombia, primarily distributed in the largely forested Río Atrato drainage. Several specimens were collected in three localities along the lower Río San Juan, however, these could’ve been anomalous specimens of S. dalyi, as many dendrobatoid species adults differ only in size and secondary sex characteristics. Its occurrence elevation is between 60 - 700 m (Grant and Myers 2013).

Life History, Abundance, Activity, and Special Behaviors
Possibly diurnal, all specimens collected were found during the day. The specimens were collected in shady lowland forest ridges and in the leaf litter (Grant and Myers 2013).

Little information is known about the reproduction and development of the species. Referring to the life history of its congeners, it is expected that females adults would lay eggs in the leaf litter, and male nurse frogs would transport the back-riding larvae to water bodies. CITATION NEEDED

Larva
Tadpoles are unknown. In the four members of the genus with known larvae, an umbelliform oral disc is present, along with tiny submarginal papillae and shallowly emarginate posterior labium (Grant and Myers 2013).

Trends and Threats
Little is known about the population size and trends of S. minutissima. Although this species occurs in a remote area that’s unlikely to be affected by human activities in the short term, it has been listed as “Near Threatened” by IUCN because of it’s limited range to only a small region of approximately 15,925 km². Logging and mining activities in the region could pose threats to S. minutissima and its habitat (IUCN 2020).

Possible reasons for amphibian decline

General habitat alteration and loss
Habitat modification from deforestation, or logging related activities

Comments
The species epithet, “minutissima” is a Latin adjective denoting “extremely small”, referring to the fact that this is the smallest species of the genus, even smaller than the “very small” minima (Grant and Myers 2013).

References
Grant, T., Myers, C.W. (2013). Review of the frog genus Silverstoneia, with descriptions of five new species from the Colombian Choco (Dendrobatidae: Colosteninae). Amer Mus Novitates 2784, 1-58. [link]

IUCN SSC Amphibian Specialist Group. (2020). “Silverstoneia minutissima (amended version of 2017 assessment).” The IUCN Red List of Threatened Species 2020:e.T78586339A177155387. https://dx.doi.org/10.2305/IUCN.UK.2020-3.RLTS.T78586339A177155387.en. Accessed on 07 May 2022.

Species Account Citation: AmphibiaWeb 2023 Silverstoneia minutissima <https://amphibiaweb.org/species/8082> 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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