Finding a new monkey species in the 21st century is exceptionally rare. Primates are among the best-documented mammals, so scientists don’t often encounter an entire population that has remained unknown to science.

But the dense rainforests of the Democratic Republic of the Congo still hold surprises.

After an investigation spanning more than a decade, an international research team has formally described a small black monkey with striking orange-cream markings around its mouth and nose. The species has been named Colobus congoensis, while researchers recommend the local name Likweli as its common name.

Original photos of Likweli. Image credits: John A Hart et al. / PLOS One (2026).

Likweli (Colobus congoensis) is only the fifth African monkey species discovered from a previously undocumented population in the past 75 years. It’s currently known from an estimated range of just 1,700 square kilometers in and around Lomami National Park, between the Lomami and Congo, or Lualaba, river systems.

They seem to only occupy a tiny range in remote parts of the Congo Basin. This makes them very vulnerable. The researchers propose that the species receive a preliminary Endangered classification because of its apparent rarity, restricted distribution, and vulnerability to hunting and habitat degradation.

“Discovering a monkey species previously unknown to science is extraordinarily rare, and it highlights how much remains to be documented in the Congo Basin and how urgent it is to protect the small area where this species is found,” Kate Detwiler, one of the researchers and an expert in biological sciences from Florida Atlantic University (FAU), told Nature.

The first clue appeared in 2008.

Conservationists Ashley Vosper and Bernard Ikembelo were exploring the Lomami Basin when they photographed part of an unfamiliar monkey high in the forest canopy on the eastern bank of the Lomami River. Only a portion of the animal was visible, but the field team thought it didn’t quite match any monkey already known from the region.

But the trail went cold.

Nothing more was reported until November 2018, when a surveillance patrol led by Jean-Pierre Kapale photographed a black monkey with pale markings around its mouth and a conspicuous white patch beneath its tail. This time, the photographs clearly showed features different than those of other primates living in the area.

This was definitely a new monkey.

Kapale and his colleagues intensified the search, documenting the species seven more times over the following 10 months. When researchers compared the new photographs with the partial image from 2008, they concluded that both showed the same mysterious animal.

A review of older patrol records then produced another surprise. A different team had photographed the monkey in August 2018, about 35 kilometers north of Kapale’s sighting. However, the animal had been misidentified in the original patrol report, and the photograph attracted no attention at the time.

Difficult to find

Researchers subsequently expanded surveys across Lomami National Park and the surrounding buffer zone. Between 2018 and 2022, they recorded 114 detections of Likweli through direct sightings, photographs and vocalizations. Systematic patrols, line-transect surveys and dawn-call monitoring intensified from 2020 onward.

The monkey proved difficult to study. It usually remained in the middle or upper canopy, and observed groups ranged from one to 20 animals, with an average of about six. Researchers also frequently saw Likweli travelling alongside other monkey species.

Even people living near its range rarely recognized it.

“As part of our search, we interviewed people in 52 villages close to where the animals live. And only people in eight villages (had ever seen) them,” Junior Amboko, one of the study authors and a PhD student at FAU, told the BBC.

Members of the Balanga ethnic group supplied the name Likweli. Mituku communities on the eastern side of its range called it kasaba nkoni, meaning “branch shaker.” But no one was really aware that this was a new species.

Four lines of evidence point to one conclusion

Photographs and field observations alone couldn’t establish that Likweli was a distinct species. The researchers needed several independent forms of evidence.

An important opportunity came in April 2021, when park patrols confiscated three dead Likweli monkeys from hunters. The specimens (one adult male and two adult females) allowed researchers to examine the animals’ skeletons, teeth, skins and DNA. They also compared them with colobus specimens held in Those comparisons revealed a distinctive combination of features.

Likweli has glossy black fur, a long black tail, prominent folded ears and long facial hairs. Its most obvious feature is the patch of pinkish-orange to cream-colored skin surrounding its mouth and extending toward its nose. Both sexes also possess a white patch beneath the tail, although its appearance differs between males and females..

Those comparisons revealed a distinctive combination of features.

Likweli has glossy black fur, a long black tail, prominent folded ears and long facial hairs. Its most obvious feature is the patch of pinkish-orange to cream-colored skin surrounding its mouth and extending toward its nose. Both sexes also possess a white patch beneath the tail, although its appearance differs between males and females.

The species is unusually small for its genus. Available measurements indicate that it has a lower body mass and a smaller skull than any other recognized Colobus species. Adults weigh roughly 7 kilograms, or about 15 pounds.

Its voice provided another clue.

Like other colobus monkeys, Likweli produces loud, low roaring calls that can travel through dense forest. Researchers found that its roars have a rapid pulse rate, a relatively high fundamental frequency and a distinctive snort between sequences. The calls most closely resemble those of the black colobus, Colobus satanas. Yet differences in their sequence, frequency modulation and resonance helped distinguish the two species.

Genetics provided the last critical bit of evidence. DNA analysis showed that Likweli’s closest known relative is the black colobus monkey (Colobus satanas), which lives more than 1,200 kilometers away in western Central Africa. However, despite their similarities, genetic data indicated that the two lineages have been evolving separately for millions of years. 

“What makes Colobus congoensis such an important discovery is that the evidence for it being a previously undescribed species came from several independent sources,” Detwiler added.

Depending on the analytical method used, the study authors estimated their most recent common ancestor lived roughly between 4.1 and 5.8 million years ago—one of the deepest evolutionary splits known within the Colobus genus.

This convergence of anatomical, genetic, behavioral, and acoustic evidence convinced researchers that Likweli represents a previously undescribed species. It emerged from a population that scientists did not know existed.

Discovered at the edge of survival

The researchers emphasize that Congolese field scientists, park patrols and neighboring communities were central to the discovery.

First author John Hart said the species would probably never have been documented without Congolese explorer-naturalists who recognized that they were seeing an unfamiliar animal and made the extra effort to photograph, track and study it.

The finding demonstrates how much remains unknown about the Congo Basin, even among large and relatively well-studied mammals. It also offers clues about how a monkey could remain scientifically undocumented for so long. Previous studies in the Congo Basin have shown that major rivers can isolate animal populations for millions of years, allowing them to evolve independently. For Likweli, that long isolation may have helped create a distinct evolutionary lineage. However, the same isolation that helped shape the species may now threaten its future. 

Hunting, settlement expansion and future conversion of forest in the park’s buffer zone could place additional pressure on the population. At least 15 new villages appeared within or near the species’ range between 2015 and 2023, according to data cited by the research team.

For those reasons, the authors propose a provisional Endangered classification under IUCN Red List criteria. Protecting Lomami National Park, limiting hunting and working with neighboring communities will be essential, they argue.

Many basic questions remain unanswered. Scientists still don’t know Likweli’s total population, diet, reproductive behavior, social organization or broader ecological role. More surveys—and ideally more comprehensive genomic data—will be needed to understand both its evolutionary history and its chances of survival.

For now, the discovery is both exhilarating and unsettling. Scientists have added a remarkable new monkey to the tree of life. They have also discovered it at a moment when its future may already depend on swift protection.

The study is published in the journal PLOS One.