Three Southeast Asian Langurs Are Distinctly Different Species

The newly described East Sumatran banded langur (Presbytis percura) qualifies as critically endangered—it’s now one of the rarest and most imperiled primates. Photograph by Andie Ang

New findings, published Scientific Reports, have identified that langurs found in Myanmar, Thailand, Malaysia, Singapore, and Indonesia, are actually three distinct species. By studying DNA found in the monkey’s droppings, the researcher were able to identify this taxonomical error in a non-invasive manner. Andie Ang, co-author and research scientist at the Wildlife Reserves Singapore Conservation Fund, pioneered this method of in his work over a decade ago with langurs. Langurs are notoriously difficult to observe—rare, flighty, spending most of their time in treetops. Andie was able to gather genetic information from langur scat.

The Robinson’s banded langur (Presbytis robinsoni) is still classified as “near threatened,” whereas the two other new species—Raffles’ banded langur and the East Sumatran banded langur—qualify as critically endangered. Photograph by Andie Ang

For two of the newly understood monkey species, the Raffles’ banded langur (Presbytis femoralis) and the East Sumatran banded langur (Presbytis percura), this new discovery of re-classification brings urgent conservation concerns, as they now qualify as critically endangered due to small populations and limited ranges. Ang estimates that the Raffles’ banded langur’s total population hovers around just 300 to 400 individuals. The other langur species, the Robinson’s banded langur (Presbytis robinsoni), on the other hand, is more widespread, and is still classified as “near threatened” by the International Union for Conservation of Nature.

Researchers examined the genome of the related white-thighed langur (Presbytis siamensis) to learn more about the evolutionary history of the new species. Scientists suspect the Riau pale-thighed langur, found only in Sumatra’s Riau Province, likely constitutes another new, critically endangered species. Photograph by Lee Zan Hui

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