Museum DNA reveals: Three frog species from the Atlantic Forest have long been extinct

A recent study shows that three Brazilian amphibian species are now considered extinct—decades after their disappearance. A formal assessment by the IUCN is still pending, but the genetic and historical evidence leaves little doubt about the loss of these species.

Published in the Bulletin of the American Museum of Natural History, the study by an international research group used state-of-the-art DNA analyses from historical museum specimens to clearly identify three frog species from Brazil’s Atlantic Forest—and at the same time declare them extinct: Dryadobates capixaba, D. carioca, and D. olfersioides.

Using museum DNA to reveal lost species

The team led by herpetologist Taran Grant (University of São Paulo) analyzed museum specimens up to 100 years old, from which so-called historical DNA (hDNA) was extracted—despite preservation damage caused by formalin and alcohol. This technique, known as museomics, originated in paleogenetics and allows comparisons between type specimens and present-day populations.

Until now, only a single species of the subfamily Allobatinae was considered widespread in the Atlantic Forest: the Rio Rocket Frog, Allobates olfersioides. Because of their quick movements, the tiny ground-dwelling frogs are also called “Rocket Frogs”. Their external appearance is very similar, so it was long assumed that they all belonged to the same species, even though they came from different regions.

The new study now shows that they are several genetically clearly distinguishable species that look almost identical externally. To do justice to this diversity, a new genus was introduced: Dryadobates. Today, all Rocket Frogs of the Atlantic Forest belong to this genus. Three of the at least twelve species known so far are considered extinct.

Portraits of the three vanished frog species

1. Dryadobates capixaba

• Type locality: Refúgio Sooretama, Linhares in the Brazilian state of Espírito Santo
• Holotype: adult male, collected on November 5, 1964
• Size: adult males 13.1–14.7 mm long, adult females unknown
• Characteristics: brown to dark brown with spots, dark flanks with a pale lateral line
• Behavior: probably diurnal with acoustically conspicuous courtship behavior (exact calls unknown), ground-dwelling in humid lowland rainforests
• Last confirmed sighting: 1975—not detected since then despite targeted searches (including with eDNA). If they still existed, they would probably have been heard or seen, because they are diurnal and acoustically conspicuous.

2. Dryadobates carioca

• Type locality: Represa Rio Grande, Jacarepaguá, in Parque Estadual da Pedra Branca, state of Rio de Janeiro, Brazil
• Holotype: adult female—collected on June 27, 1967
• Size: males: 14.6–16.1 mm, females: 15.8–17.8 mm
• Characteristics: brown back with dark spots, cream-colored stripe from the belly to the snout
• Behavior: ground-dwelling in primary forest, diurnal
• Last record: not observed again since its first description in 1967; intensive field research (for example in November 1999) was also unsuccessful

3. Dryadobates olfersioides

• Type locality: Angra dos Reis, state of Rio de Janeiro, Brazil
• Lectotype: adult male, collected in April 1924
• Size: males: 17–18.8 mm (largest known species of the genus); females unknown
• Characteristics: uniformly brown, flanks with a diffuse pale line and cream-colored spots
• Behavior: unknown; probably diurnal like other Dryadobates species and ground-dwelling in humid primary forest
• Last record: January 1975 and December 1981; despite intensive field research in the region, it has not been found again since

Why the Dryadobates species disappeared—and why this is not an isolated case

All three probably extinct Dryadobates species were endemic to Brazil’s Atlantic Forest—one of the most species-rich yet also most threatened ecosystems on Earth. Today, only about 12% of the original forest area remains, mostly in the form of small, isolated fragments. This is exactly what proved fatal for the tiny ground-dwelling frogs.

Dryadobates species are probably not very mobile and depend on a humid microclimate in intact rainforest soil. The fragmentation of their habitat by roads, cities, or plantations not only led to increasing isolation but also reduced genetic diversity. This increased their vulnerability to diseases, climate fluctuations, and other stress factors. Many of these species occurred only in extremely small areas anyway; in some cases, only a single locality is documented.

In addition, urbanization, changed water availability, light pollution, or climate change may have contributed to their extinction. This is particularly clear in D. carioca and D. olfersioides: their type localities are now in urban fringe zones of Rio de Janeiro that have changed massively in recent decades.

The disappearance of three Dryadobates species is not an isolated case, but part of a worrying trend. A 2024 study published in the journal Science showed that more than 80% of the endemic tree species in the Atlantic Forest are threatened with extinction. Other animal species are affected as well—for example the large, black-plumaged Alagoas Curassow (Mitu mitu), which is now considered extinct in the wild. Its story resembles that of Dryadobates: habitat loss, forest fragmentation, lack of protection.

About the genus Dryadobates

The differences between the Allobates species of the Amazon region and those of the Atlantic Forest made it necessary to introduce a new genus for the latter: Dryadobates. The newly introduced genus Dryadobates currently comprises at least twelve species, all endemic to the Atlantic Forest. It belongs to the family Aromobatidae (subfamily Allobatinae) and is the sister group of all other Allobatinae.

Several characteristics are typical of the genus Dryadobates:

• Calling behavior: Males call with single, short notes—a conspicuous distinguishing feature from other groups.
• Reproduction: Male parental care, in which the tadpoles are probably actively transported to water bodies by the males.
• Habitat: The animals live close to the ground in humid primary forests, often in leaf litter.
• Body size: Most species are tiny—often only 1.5 to 2 centimeters long, about the size of a human fingernail.

Dryadobates belongs to the group of so-called “Nurse Frogs”—a term for tropical frogs with pronounced parental care, in which the males guard or transport tadpoles.

Despite their small size, these inconspicuous frogs play an important role in the humid soil ecosystem of rainforests. They are indicators of intact microhabitats and are particularly vulnerable to environmental change because of their small distribution ranges.

When false assumptions endanger species

Because the Rio Rocket Frog (Allobates olfersioides) was once considered a widespread species that united many populations in the Atlantic Forest, it was listed as “least concern” on the IUCN Red List. But the new study shows that this supposedly widespread species was in fact a complex of several locally endemic species, three of which have now disappeared.

“The realization that this is not one widespread species but several narrowly restricted species changes everything,” study leader Taran Grant told Agência FAPESP. “The Atlantic Forest is highly fragmented and vulnerable to habitat loss—each of these species therefore faces its own specific threats that require individual conservation measures.”

Hope & need for action

Of the remaining nine known Dryadobates species, some are known from only a single locality. Two more are currently known only from museum collections. They may already be extinct as well. If this is confirmed, almost 40% of all known species in this genus would have disappeared in just 50 years. This shows the urgency of targeted conservation measures and more intensive field research. Even if some species are considered “least concern”, they may in reality already have disappeared.

But there is also hope: large parts of the rainforest in Rio de Janeiro, Espírito Santo, and Bahia have not yet been intensively researched. New species could be discovered, or lost ones found again.

---

Sources

• Grant, T., Lyra, M. L., Hofreiter, M., Verdade, V. et al. (2025). Museomics and the systematics of the Atlantic Forest nurse frogs (Dendrobatoidea: Aromobatidae: Allobatinae). Bulletin of the American Museum of Natural History, 472, 1–76. https://doi.org/10.1206/0003-0090.472.1.1
• Julião, A. (2025, July 16). Historical and current population DNA reveals that there are at least 12 species of rocket frogs, three of which are already extinct. Agência FAPESP. https://agencia.fapesp.br/historical-and-current-population-dna-reveals-that-there-are-at-least-12-species-of-rocket-frogs-three-of-which-are-already-extinct/55323