Our top “most wanted” lists by groups of species include those species that have been lost to science for at least a decade (and often for much longer!) and, like our top 25 “most wanted” species, may be lost for a variety of reasons. We worked with various IUCN Species Survival Commission Specialist Groups and other partners to determine these lists of flagship species. In some cases, biologists may be actively out searching—or interested in going out to search—for these species. In other cases, these species represent the kinds of compelling stories that can help raise their group’s public profile, even if nobody is out actively looking. They represent a broad geographical reach, and may present opportunities for inspiring conservation action.
Scarlet Harlequin Frog
SCIENTIFIC NAME: ATELOPUS SORIANOI
LAST SEEN: 1990 IN VENEZUELA
YEARS LOST: 28
The rediscovery of the Scarlet Harlequin Frog could be the key to better understanding how species rebound from the chytrid fungus that has decimated amphibians worldwide and hit harlequin frogs particularly hard. The Scarlet Harlequin Frog has the most restricted geographic range of any Venezuelan Atelopus species and is known from a single stream in an isolated Venezuelan cloud forest. Anecdotal reports from locals indicate that it could be surviving in a remote patch of cloud forest that researchers have not yet surveyed.
Gastric Brooding Frogs
Scientific name: Rheobatrachus silus and Rheobatrachus vitellinus
Last seen: 1981 (R. silius) and 1985 (R. vitellinus) in Australia
Years lost: 37 and 33
Both species of Gastric Brooding Frog are endemic to Australia. And, according to the IUCN Red List, both may be extinct. The only two species in the genus Rheobatrachus, R. silus and R. vitellinus, have not been seen in the wild since 1981 and 1985, respectively, despite extensive searches. Gastric Brooding Frogs are named for their unusual breeding biology—females lay and then ingest their eggs. During this gestation period, females stop producing hydrochloric acid, a powerful digestion enzyme produced in their stomach. Six weeks later, mothers “birth” their young through regurgitation, releasing fully formed froglets into the world. Researchers believe that the ability of these organisms to stop producing stomach acid could provide new insights into stomach ulcer treatments and methods to help patients recover from stomach surgery more quickly. The causes for the decline in Gastric Brooding Frog populations are unknown, though biologists suspect habitat loss and disturbance has played a role.
Calilegua’s Marsupial Frog
Scientific name: Gastrotheca christiani
Last seen: 1996 in Argentina
Years lost: 22
This native Argentinian frog has not been seen in the wild since 1996. A complex mix of threats including habitat loss, climate change, and chytridiomycosis, a deadly amphibian pathogen, has contributed to the decline of the Calilegua’s Marsupial Frog. This species was difficult to find in its home in the canopy of Neotropical forests even before its population began to decline. As its name suggests, Calilegua’s Marsupial Frog has a marsupial pouch, making it different from other frog species biologically. Unlike the majority of known frogs, this species hatches and raises its young in the mother’s pouch. If rediscovered, Calilegua’s Marsupial Frog would become a flagship species for amphibian conservation in Argentina, a global biodiversity hotspot. In 2017, a team of biologists recorded a sound that could be the species—they’re working to find individuals in the area where they recorded the sound of a “funny thing.”
Scientific name: Incilius periglenes
Last seen: 1989 in Costa Rica
Years lost: 29
Though it used to be abundant in the cloud forests of Monteverde, the Golden Toad vanished at the end of the 1980s. It was last seen in the Reserva Biológica Monteverde, Costa Rica in 1989. Individuals of this species exhibit extreme sexual dimorphism, with males distinguished by the bright orange color that is alluded to in the species’ name. Females of this species also possess unique coloration and can be differentiated by their red patches, surrounded by black and yellow edges. This species is an explosive breeder and toads emerge from the ground following rains to breed en masse for a few days to weeks. It resides in the cloud and elfin forests protected by the Reserva Biológica Monteverde and can be found at elevations 1,500 to 1,620 meters above sea level. Threats including climate change, chytridiomycosis, and airborne pollution, combined with its restricted range, likely contributed to this species’ potential extinction.
Scientific name: chiasmocleis sapiranga
Last seen: 2005 in Brazil
Years lost: 13
The Humming Frog is one of the rarest frog species in the Atlantic Coastal Forest of Bahia, Brazil. Despite targeted attempts to find this species in the wild, the Humming Frog has not been seen since 2005, when it was registered on the east margin of the Timeantube River. Currently, researchers believe this species occurs within an area locally known as the Sapiranga Reserve, which is characterized by a mosaic of sand dunes, dry forest and secondary rainforest. The reserve measures more than 500 hectares, but is threatened by habitat loss. Historically, Humming Frogs could be found and recorded after strong monsoon storms on the coast. As a result, scientists leading the search for the Humming Frog explore the coast for this species right after monsoons.
Northern Darwin’s Frog
Scientific name: Rhinoderma rufum
Last seen: 1981 in Chile
Years lost: 37
The Northern Darwin’s Frog has eluded scientists since 1981, with the last official sighting in Río Ramadillas, Chile. Prior to 1978, this species was regularly found in small, isolated subpopulations in Chile, from Zapallar to Ramadillas. This species exhibits a unique and unusual breeding strategy—males hatch their young in their vocal sacs, storing them until they mature to tadpoles with keratinized jaws. For this reason, National Geographic has crowned this frog the “epitome of daddy daycare.” Scientists believe this species is Critically Endangered and possibly extinct as a result of the failure of past targeted attempts to find the Northern Darwin’s Frog. Biologists hypothesize that habitat loss and chytridiomycosis, a deadly pathogen responsible for declining amphibian populations worldwide, are to blame for the disappearance of the Northern Darwin’s Frog, though the reasons for its sudden decline remain enigmatic. The IUCN SSCAmphibian Specialist Group is helping to develop a conservation strategy for this species and sister species Rhinoderma darwinii, or Darwin’s Frog.
La Visite Robber Frog
Scientific name: Eleutherodactylus glanduliferoides
Last seen: 1985 in Haiti
Years lost: 33
The current status of the La Visite Robber Frog is Critically Endangered on the IUCN Red List, though it may already be extinct. If it’s not already extinct, biologists believe the entire population may be restricted to a small locality within the Massif de la Selle, in Haiti, making them even more at risk. This terrestrial species breeds through direct development, which means that it skips the tadpole stage, and resides in the moist forests at high elevations. Land management activities involving charcoaling and slash-and-burn agriculture are believed to be the main sources of habitat destruction threatening this species’ survival.
Overlooked Squeaker Frog
Scientific name: Arthroleptis kutogundua
Last seen: 1930 in Tanzania
Years lost: 88
The Overlooked Squeaker Frog is an apt name for this species, which is only known to reside in the Ngozi Crater in the Poroto Mountains of Tanzania and has been missing since 1930. Since its discovery in 1930, only a single specimen has been recorded, resulting in a lack of data describing this species’ habitat and ecology. Human encroachment in the Ngozi Crater has resulted in the degradation of natural habitat in this area. As a result, biologists believe habitat loss is primarily responsible for the decline and possible extinction of the Overlooked Squeaker Frog.
Scientific name: Hynobius turkestanicus
Last seen: 1909 in Turkmenistan
Years lost: 109
“Head compressed, longer than broad. Snout rounded, the length equaling interorbital width.” These descriptions represent some of the only known details about the Turkestanian Salamander, which has been missing for more than a century. In fact, this species is only known from a few individuals collected at the beginning of the 20th century—since then, all specimens have been lost, as have all records of the salamander’s exact location. If not extinct, the species may reside in the area between Pamir and Samarkand, in Kyrgyzstan, Tajikistan, or Uzbekistan. Similar to other known salamander species, the Turkestanian Salamander is presumed to breed in water and live on land as an adult.
Yunnan Lake Newt
Scientific name: Cynops wolterstorffi
Last seen: 1979 in China
Years lost: 39
The Yunnan Lake Newt was last seen in China nearly 40 years ago. Numerous attempts to locate this species have failed to record any individuals in known and expected habitats, such as Kunming Lake and the surrounding areas in Yunnan, China. Scientists point to pollution, land reclamation, and the introduction of exotic fish and frog species as the central causes of the Yunnan Lake Newt’s decline.