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.


Mount Kenya Potto

Scientific name: Perodicticus potto stockleyi 

Last Seen: 1938 in Kenya

Years Lost: 80

In the misty highland forests of Mount Kenya, there lives a small primate of disputed taxonomy. Known from only one specimen collected in 1938, The Mount Kenya Potto is a subspecies of potto—but whether of the Eastern or Western Potto, scientists are currently debating. Pottos are small, nocturnal primates with tiny, stumpy tails—and they’re exceptionally difficult to study. Their nocturnal, shy, quiet, and well-camouflaged lifestyle makes them cryptic in even the best surveying conditions. 

Whether the Mount Kenya Potto is a subspecies of the Eastern or the Western Potto, scientists agree that this subspecies is in trouble. Native only to the forests around and on Mount Kenya itself, the animals are either very rare or extinct. Recent surveys—as far back as 1999—have failed to detect any Mount Kenya Pottos on Mount Kenya. Their limited range and their reliance on wet forest habitat have made them vulnerable to human encroachment, deforestation, and general habitat disruption.


Sody’s/Bangka Slow Loris

Scientific name: Nycticebus bancanus

Last seen: 1937 on the island of Banka

Years lost: 81 years


A little red-backed, big-eyed, hairy-eared pale-masked mammal is missing on the island of Banka. The island, nestled between Sumatra and Borneo, is famous for its tin mines and its mineral extraction disputes. The Bangka Slow Loris was, or perhaps still is, native to the island as well as to a little sliver of Borneo itself. But this species has been lost to the annals of science. Slow loris are small, nocturnal, and excellent hiders—all of which makes it difficult to ascertain their presence or absence in any given area. They’re also crimson red.

Recent studies have failed to find almost any of the Bornean slow loris throughout their historic range. And Banka, with its encroaching mining operations and disappearing natural landscapes, is especially at risk. 

Illustration by Toni Llobet from: Wilson, D.E., Lacher, T.E., Jr & Mittermeier, R.A. eds. (2016).  Handbook of the Mammals of the World . Vol. 6. Lagomorphs and Rodents I. Lynx Edicions, Barcelona.

Tenasserim Langur

Scientific name: Trachypithecus barbei

Last Seen: 1970s in Myanmar

Years Lost: 40-ish

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Perhaps Asia’s most mysterious primate, the Tenasserim Langur was known only from a handful of museum specimens and decades-old field observations. Until the lost langur turned up in an unexpected spot—the Bangkok Zoo. The langur is a small animal who peers at the world through a white mask.

Native to the Tenasserim region of Myanmar from which it gleans its names, as well as from neighboring Thailand, scientists lack the information to even assess what kind of habitat the primate prefers. The hills include both deciduous and coniferous trees, but no one knows where the langurs lurk—or if they even still survive in the wild. Because there is still good forest cover remaining in the area, especially on the Myanmar side, biologists remain hopeful.

© Charles H. Smith

© Charles H. Smith

Miss Waldron's Red Colobus

Scientific name: Piliocolobus waldronae

Last seen: 1978 in Côte d’Ivoire

Years lost: 40


Miss Waldron’s Red Colobus came close to claiming the dubious honor of being the first primate to be declared extinct in more than 500 years after repeated failed searches. But evidence from hunters appeared in 2000 and 2001 that suggested that a very small number of these monkeys may be living in the southeast corner of Côte d'Ivoire. Miss Waldron’s Red Colobus was first discovered in 1933 by a British museum collector who named it after a colleague on the expedition, Miss F. Waldron, with the last conclusive sighting of the monkey in 1978. No photographs or video of the species alive exist.

Illustrations by Toni Llobet from: Wilson, D.E., Lacher, T.E., Jr & Mittermeier, R.A. eds. (2017).  Handbook of the Mammals of the World . Vol. 7. Rodents II. Lynx Edicions, Barcelona.

Lang’s Red Colobus

Scientific name: Piliocolobus langi

Last Seen: 1980s in the Congo

Years Lost: 35ish


A striking dark monkey with a mantle of red, Lang’s Red Colobus is native to the Congo. Primatologist Marc Colyn saw more than 360 dead Lang’s Red Colobus, as well as some living and thriving ones, near Kisangani, DRC in the 1980s. Since then, no researchers have been able to detect their presence. Two of these monkeys, killed by hunters, turned up in 2012. Since then, no other sightings have been recorded, despite dedicated searches of its former range, including one this year. Like many of the other red colobus species, it has been devastated by hunting and habitat loss.  


Eastern Red Colobus

Scientific name: Piliocolobus semlikiensis

Last Seen: 1991 in Uganda

Years Lost: 27

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The Semliki Red Colobus was first described only in 1991—at which point it may have already been on the brink of extinction. This black-backed and white-bellied monkey sports an elegant long tail and striking sweeps of red coloration down its sides. The Semliki River, which connects Lake Edward to Lake Albert, flows through the famed Virunga National Park, as well as the Mt. Hoyo Reserve. Semliki Red Colobus Monkeys lived in the forests of western Uganda in the middle of the 20th century. Rumors persist that some populations of the species may survive in the area despite widespread deforestation and political unrest, but no sighting has been verified in more than two decades.