Meet Cercopithecus lomamiensis, a newly discovered species of African monkey found in central Democratic Republic of Congo (DRC). Together with the 'honk barking' Highland mangabeys (Lophocebus kipunji) of Tanzania, C. lomamiensis is only the second new species of monkey discovered in Africa in the past 28 years.

Described in PLoS One this week by scientists led by conservation biologist John Hart from the Lukuru Wildlife Research Foundation in the DRC, the discovery occurred in 2007 when a pet juvenile female was found at the home of a primary school director in the town of Opala. Hart and his team had come to a region in central DRC called the Tshuapa-Lomami-Lualaba Conservation Landscape (TL2), which is the land between the Tshuapa, Lomami and Lualaba rivers, to explore the largely unknown, vast and roadless forest within. Upon visiting this pet monkey, Hart found that the locals identified the animal as 'Lesula', and the species, although not known to science at the time, was well known by hunters.

"He [the school director] reported that he acquired the infant about two months earlier from a family member who had killed its mother in the forest near Yawende, south of Opala and west of the Lomami River," the team reported. "We took photographs of the animal and made arrangements for its care. We observed and photographed this animal regularly over the next 18 months."

More searching in Opala resulted in another captive male and female Lesula, and these two were monitored for several months. Then, in December 2007, the team saw their first wild Lesulain the Obenge region along the Lomami River. They were instructed by Hart to collect photos of hunters’ kills of the animal and a snip of skin or a whole carcass to send to specialists for analysis.

Hart's team sought the help of geneticists working at New York University and morphologists at Yale University's Peabody Museum to analyse information gleaned from 48 individuals, as well as an audiologist who could analyse the Lesula's low frequency 'boom' calls. The analysis took over three years to complete. "Our conclusion: This is a new species of monkey," Hart's wife, Therese, a member of the team, reported on their blog. "Its home is the TL2 Landscape, west of the Lomami River [hence its scientific name]. It is separated by two major rivers from its closest relative, the owl-faced monkey."

While Lesula and owl-faced monkeys (Cercopithecus hamlyni) have quite similar faces, the Lesula's colourings set it apart from any other species. As an adult, its pink, naked facial skin and muzzle are framed by a long mane of blonde hairs flecked with brown. A pale stripe of yellowish-cream skin runs down its nose, like the more distinctive flash of white running down the dark facial skin of C. hamlyni.

The species' medium-sized frame is covered in brown fur with a distinct amber patch running down its back, and its legs and most of the length of its tail are a striking black. Its large, hooded eyes are also a deep amber. Adult males are 47–65 cm long and weigh 4–7.1 kg, while the females measure 40–42 cm and weigh 3.5–4 kg. Like C. hamlyni, the Lesula male also boasts bigger canines and bright blue skin covering the scrotum, buttocks and perineum - the area between the pubic arch and the anus - which reportedly fades to white when a Lesula is killed and its skin dried.

The main obstacle in declaring this a new species was distinguishing it from C. hamlyni. A morphological analysis revealed that Lesula has larger eyes that sit more closely together in the skull, and larger incisors, both on the upper and lower jaw. The males' deep, descending boom, which is emitted exclusively at dawn, is similar to, but slightly different to that of C. hamlyni, and unlike that of C. hamlyni, can be elicited by imitating eagle calls. Lesula is said to occupy a range of around 17,000 km2 of forests in DRC’s eastern central basin, and is separated by both the Congo (Lualaba) and the Lomami Rivers from C. hamlyni, which occupies a range of around 180,000 km2.

The team reports that the Lesula is quite common in the TL2 region, and has remained hidden for so long because the forest here has not been well-explored by scientists until recently. While there is so far no logging or mining taking place in the region, hunting represents an immediate threat to the species' survival, according to the researchers. "For species with restricted ranges and reliance on primary forest, such as C. lomamiensis, uncontrolled hunting can lead to catastrophic declines over a short period," the researchers state, calling for heightened conservation efforts and hunting controls to be established.

Click here to see a terrifying camera trap shot of a Lesula on the Harts' blog.

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