Conservationists spot a new, unidentified monkey in a forest in Borneo. According to a recent study, the primate is a rare hybrid between two distinct species. Experts said that the species this monkey originated from are mortal enemies and compete for a greater territorial space in the jungle.

The mystery monkey is likely an offspring of the proboscis monkey known as the Nasalis larvatus and the species of silvery langur or Trachypithecus cristatus. Based on records, these two factions are distant cousins that have shared the same habitat longer since their discovery.

Discovery of Malaysian Borneo's Rare, Mystery Monkey

Is Malaysia’s “mystery monkey” a hybrid between Nasalis larvatus and Trachypithecus cristatus? An assessment of photographs
(Photo: Springer Nature, Ruppert et al.)
A. Juvenile “mystery monkey” near Kampung Bilit, Kinabatangan, Sabah, groomed by adult female Trachypithecus cristatus (likely the mother) (photo by Ken Ching, June 19, 2017). B. Subadult “mystery monkey,” alone (photo by Ben Duncan Angkee, November 17, 2018). The individual may appear younger in this photo because the phone camera had an automatic softening filter activated. C. Subadult “mystery monkey,” alone, feeding (photo by Bob Shaw, November 17, 2018). D. Subadult “mystery monkey” with juvenile T. cristatus (in color change phase), adult female T. cristatus, and another T. cristatus individual while grooming (photo by Ken Ching, November 22, 2018). E. Adult male Nasalis larvatus mating with adult female T. cristatus in the same area (photo by Jean-Jay Mao, September 10, 2017). F. Adult putative hybrid now clearly identifiable as female with swollen breasts, holding an infant, which appears to be her offspring (photo by Nicole Lee, September 7, 2020)

Due to the strict protocols brought by the pandemic, the authors of the study had limited resources to analyze the unknown monkey. Instead, the experts began the investigation by comparing the photographs of the primate taken in 2017, back when their existence first gained the scientific community's attention.

The first images of the infrequent monkey showed it in its juvenile stage. Recent photos were taken back in 2020 presented sightings of a larger monkey, accompanied by its infant offspring.

Universiti Sains Malaysia's School of Biological Sciences specialist Nadine Ruppert, who served as the lead of the study, explained in a Live Science report that the rare monkey might have produced a child and seems to be nursing is based on the images taken from the forest.

Many species, such as those who belong to the primate groups, have little to no tendency to mate with others. However, very close relatives, such as Thailand's northern pig-tailed macaques (Macaca leonina) and southern pig-tailed macaques (Macaca nemestrina), are compatible for interbreeding.

This baffles scientists, as the Borneo monkeys Nasalis larvatus and the Trachypithecus cristatus do not come from the same genus.

The hybrid monkey was located in the Malaysian Borneo's Kinabatangan River. In preservation records, most of the primate population on the island where the river flows is only filled by the factions of the proboscis monkeys and silvery langurs.

Female individuals dominate both species. Males from each group are destined to leave their communities once they reach adulthood to start or capture another group independently.

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Hybrid Monkey: A Warning About Borneo's Primate Habitat

Proboscis monkeys have distinctive pinkish faces and elongated noses. Silvery langurs have dark faces with shorter and flatter noses.

Comparing the two, the proboscis monkeys are quite larger, growing up to 76 centimeters in height and 24 kilograms in weight. Adult silvery langurs develop with a height of 56 centimeters and a maximum weight of 6.6 kilograms.

The authors concluded that the existence of the Bornean hybrid monkey was due to the overlapping social behavior of the two species.

The male proboscis monkeys likely mate with female silver langurs. Ruppert said there are certain areas where female proboscis monkeys even nurture the infant silver langurs.

These activities and the presence of Malaysia's mystery monkey are possible effects of the two species cramping up on the island. According to Ruppert's team, the region contains only the remaining patches of forests surrounded by oil palm plantations, and this escalates the species' competition further.

Ruppert added that the mystery monkey should not serve as an attraction but rather a 'flagship' that states the current situation of its parent species and their natural territories.

The study was published in the journal International Journal of Primatology, titled "Is Malaysia's "mystery monkey" a hybrid between Nasalis larvatus and Trachypithecus cristatus? An assessment of photographs."

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