7 Lost Animal Species—No One Knows Whether They Still Exist

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There are numerous lost animal species, and to this day it remains unclear whether they still exist or have long since gone extinct. Some are known only from a single museum specimen or a few specimens collected decades or even centuries ago. There have been no further records—not always because intensive searches failed to find the animals, but often because hardly anyone specifically looked for them. As a result, often very little is known about their way of life, their needs, or even their original range.

Searching is particularly difficult in remote or inaccessible regions, such as small islands, mountain forests, or poorly studied marine areas. Yet even if a species has not been documented for many decades, it is not automatically considered extinct. That would require sufficiently thorough searches over an extended period and in all suitable habitats.

Experts therefore err on the side of declaring lost animal species extinct too late rather than too soon. A premature classification can lead to the termination of search programs, the withdrawal of research funding, and an end to conservation measures for the species or its habitat. If a small population does still exist, this could deprive it of the protection it needs most urgently.

As long as comprehensive surveys have not confirmed their disappearance, the possibility remains that a few individuals still survive somewhere. The following seven species show how difficult it can be to obtain certainty.

Ethiopian amphibious rat—only one specimen from 1927

The Ethiopian amphibious rat, also known as the Ethiopian water mouse (Nilopegamys plumbeus), is known from just one male specimen. It was caught in March 1927 along a stream in the Ethiopian Highlands. No further records followed—although no one specifically searched for the species for decades.

When researchers specifically surveyed the original collection site in 2018, the former mountain stream was gone. The habitat had been almost completely converted into pasture and no longer offered suitable conditions for a semiaquatic rodent. It is therefore certain that the Ethiopian amphibious rat has disappeared from its only known collection site. No one knows whether it has survived elsewhere. The IUCN therefore lists it as possibly extinct.

What makes the Ethiopian amphibious rat special is its extraordinary adaptation to life in the water. This makes it unique among Africa’s known mice and rats. It probably hunted prey by actively swimming in the mountain streams of the Ethiopian Highlands. Other semiaquatic rodents on the African continent, by contrast, wade through shallow water or forage among aquatic plants and along the shore.

Siau scops owl—no confirmed record since 1866

The Siau scops owl (Otus siaoensis) is likewise known from a single specimen. The bird was collected as early as 1866 on the small Indonesian island of Siau north of Sulawesi. Although a five-day search for the species in 1998 was unsuccessful, it showed how dramatically the habitat had changed: much of the original forest had been cleared and replaced by plantations or scrubland. At the time, only about 50 hectares of forest were thought to remain, mostly at elevations above 800 meters.

Nevertheless, the IUCN lists the Siau scops owl not as extinct but as Critically Endangered. This is based primarily on reports by islanders who claim to have seen the bird; a video recording from 2017 may also show a Siau scops owl. However, neither the reports nor the video are considered definitive evidence, so the species is not regarded as rediscovered.

Moreover, some other Asian scops owls can survive even in heavily altered habitats—so why not the Siau scops owl? Only thorough surveys of the remaining and still inadequately studied habitats could provide certainty. If the species has indeed survived, however, its population is likely to be extremely small.

Lost shark—three specimens, the most recent from 1934

The lost shark (Carcharhinus obsoletus) is known from only three museum specimens that were collected in Southeast Asia between 1897 and 1934—one embryo and two juveniles. For a long time, the preserved animals were thought to be Borneo sharks (C. borneensis) or another species of small requiem shark. Only an examination of their teeth and other physical characteristics revealed that they differed significantly from those sharks. In 2019, the three specimens were therefore used to describe a new species—85 years after the last known record.

Exactly where the lost shark lived is unknown. The locality information points to Sarawak, Bangkok, and Ho Chi Minh City, although at least the two major cities presumably refer to the markets where the animals were found. The species probably inhabited shallow coastal waters of the southern South China Sea. The area has been fished intensively for decades, and as a shallow-water species, the lost shark would presumably have had few places of refuge there.

Despite targeted studies and regular checks of fish markets, no further specimen has been discovered since 1934. The IUCN therefore lists the lost shark as possibly extinct. Because small requiem sharks can easily be overlooked in large catches or confused with similar species, its survival cannot be ruled out entirely.

Ilin Island cloudrunner—obtained in 1953 and never found again

The Ilin Island cloudrunner (Crateromys paulus) is known from just one adult male, which a collector acquired as a preserved specimen on the small Philippine island of Ilin in 1953. Whether the animal also came from the island or was caught elsewhere remains unclear. However, archaeological finds of numerous teeth confirm that the species was native to Ilin at least in the past.

Several targeted searches in 1989, 1997, and 2000 were unsuccessful. Later camera traps likewise produced no definitive evidence. The habitat of the Ilin Island cloudrunner has now almost completely disappeared: there is no primary forest left on Ilin, only small remnants of the original karst forest among plantations and secondary vegetation.

The species may still occur on the much larger neighboring island of Mindoro. Local residents there have reported a large, tree-dwelling rat said to resemble the Ilin Island cloudrunner. Despite various surveys, its presence on Mindoro has not yet been confirmed. Because the origin of the sole specimen is uncertain and the species’ possible range is unknown, the IUCN lists the Ilin Island cloudrunner as Data Deficient. The species has probably disappeared from Ilin—but whether a small population survives elsewhere remains unknown without further targeted searches.

Negros fruit dove—known from a single female

In May 1953, a zoologist discovered a pair of doves in a tree on the Philippine island of Negros. He shot the female, while the male flew away. To this day, the species, which was named the Negros fruit dove (Ptilinopus arcanus) shortly afterward, is known from this single specimen alone.

Despite several prolonged searches, the fruit dove has not been definitively recorded since. However, there have been repeated unconfirmed reports: hunters are said to have shot birds matching the species’ description in 1985 and 2008. A possible sighting was also reported in 2002. None of these reports, however, could be scientifically confirmed.

It remains possible that the Negros fruit dove has survived. Fruit doves are considered shy and can easily be overlooked even during targeted surveys. Other threatened bird species previously known only from Negros have also been discovered on the neighboring island of Panay. Parts of the forests there remain inadequately studied.

The IUCN therefore lists the Negros fruit dove as Critically Endangered rather than extinct. If it still exists, its population probably numbers fewer than 50 mature individuals. Hunting and the continuing destruction of forests on Negros are considered the greatest threats.

Culebra giant anole—lost since 1932

The Culebra giant anole (Anolis roosevelti) is known from eight museum specimens. Six of them were probably collected as early as the early 1860s, with two more collected in 1931 and 1932 on the Puerto Rican island of Culebra. Historically, the species also occurred on Vieques, St. John, and Tortola in the eastern part of the Puerto Rico Bank.

After its scientific discovery, the Culebra giant anole was definitively recorded just once more, in 1932. Although there have been several unconfirmed sightings since 1973, most recently in 1978, none could be substantiated. Some reports of large anoles turned out to be misidentifications of green iguanas. Repeated searches on Culebra, Vieques, St. John, and Tortola were also unsuccessful.

On the four islands where the Culebra giant anole presumably lived, the original forests have been heavily altered or completely cleared. Grazing, military use, development, and tourism destroyed additional potential habitat. Introduced rats and mongooses may also have eaten eggs and adults. The IUCN lists the Culebra giant anole as possibly extinct, although there is still hope that the lizard may have survived, particularly on smaller, insufficiently surveyed islands off the coast.

Smooth handfish—first extinct, then not after all

The smooth handfish (Sympterichthys unipennis) is known from a single specimen. French explorers collected the fish in 1802 during an expedition to Australia. Its place of origin is recorded only as “Australian seas”; the animal probably came from the waters of southeastern Tasmania.

Nothing is known about either its habitat or its way of life. Related handfishes live on rocky or sandy seafloors off Tasmania. If S. unipennis also occurred in the D’Entrecasteaux Channel, intensive mussel and oyster harvesting, together with seafloor dredging, may have severely damaged its habitat. Whether this actually caused its disappearance cannot be established.

In 2020, the IUCN classified the smooth handfish as extinct because it had not been recorded for more than 200 years. This made it the first marine fish of modern times to be officially classified as extinct. The classification was challenged, however: the searches conducted to date had not been comprehensive enough to rule out the possibility that the species might still survive somewhere. The IUCN therefore reversed the classification in 2021 and has since listed S. unipennis as Data Deficient. This does not mean that the smooth handfish is likely to still exist, only that its extinction has not yet been proven beyond doubt.

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