Order : PRIMATES
Family : Cercopithecidae
Species : Simias concolor

Head-body length : 43-52 cm
Tail length : ~15 cm
Weight : 
Males to at least 7.5 kg, females to at least 6 kg
(generalised from Hadi et al, 2009).

Simias concolor (Pig-tailed Snub-nosed Monkey, Simakobu) occurs on the Mentawai islands of Siberut, Sipora, Pagai Utara (North Pagai), Pagai Selatan (South Pagai) and the smaller islands of Simalegu and Sinakak. These islands lie off the coast of Sumatra.

The species is sometimes called 'Pig-tailed Langur', but this is a misnomer as the genus Simias is part of the primate group known as odd-nosed colobines; it's nearest relative appears to be Nasalis larvatus (Proboscis Monkey) which occurs on Borneo some 1,000 kilometres to the east.

Males of this unique primate reach around 7.5 kg in weight, with females being smaller. The tail is short at around 15 cm. Fur colour is dichromatic; most adults are greyish-black, but less than one third are 'creamy-buff with brown'. Group size averages 8 to 9 individuals. (Hadi et al, 2009).

Simias concolor inhabits primary forest in the hills, and degraded secondary forest and swamp forest in the lowlands. It is semi-terrestrial in habits and feeds primarily on young leaves as well as fruits, seeds and flowers. They are known to be shy and will quickly drop to the ground and move away from any perceived threat.

This species is categorised as Critically Endangered by IUCN (Quinten et al, 2020); it is under continued threat from forest loss and hunting pressure.

Figs 1 and 2 : Adult greyish-brown example in secondary forest on South Pagai island in 2023. 

Fig 3 : Secondary forest habitat on South Pagai Island. 

All photos thanks to Andie Ang. 

References : Hadi, S., Ziegler, T., & Hodges, J. K. (2009). Group structure and physical characteristics of Simakobu monkeys (Simias concolor) on the Mentawai Island of Siberut, Indonesia. Folia Primatologica, 80(2), 74-82. 

Hadi, S., Ziegler, T., Waltert, M. et al. (2011) Habitat Use and Trophic Niche Overlap of Two Sympatric Colobines, Presbytis potenziani and Simias concolor, on Siberut Island, Indonesia. Int J Primatol 33, 218-232 (2012).

Quinten, M, Setiawan, A., Cheyne, S., Traeholt, C. & Whittaker, D. (2020). Simias concolor. The IUCN Red List of Threatened Species

Links :

IUCN assessment (2020)