The white-thighed surili (''Presbytis siamensis'') is a species of

primate Primates are a diverse order of mammals. They are divided into the strepsirrhines, which include the lemurs, galagos, and lorisids, and the haplorhines, which include the tarsiers and the simians ( monkeys and apes, the latter including ...

from the family of old world monkeys ( Cercopithecidae). This species lives arboreal amongst the sub-montane forests. It is

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found else ...

to the

Thai-Malay Peninsula The Malay Peninsula ( Malay: ''Semenanjung Tanah Melayu'') is a peninsula in Mainland Southeast Asia. The landmass runs approximately north–south, and at its terminus, it is the southernmost point of the Asian continental mainland. The ar ...

, the

Riau Archipelago The Riau Archipelago is a ''geographic'' term (as opposed to administrative region) for the core group of islands within the Riau Islands Province in Indonesia, and located south of Singapore and east of Riau on Sumatra. Before the province of R ...

and Sumatra. In addition, the white-thighed surili contain four subspecies: ''siamensis'' (

nominate Nomination is part of the process of selecting a candidate for either election to a public office, or the bestowing of an honor or award. A collection of nominees narrowed from the full list of candidates is a short list. Political office In the ...

), ''cana'', ''paenulata'' and ''rhionis'', are recognized here. Furthermore, they are characterized by the white patches located on the outside of their legs, which is what gives them their name. Additionally, they can be referred to as pale-thighed langur/surili. These primates are an important species for the diversity of forest environments in the Malaysian area.

Description

Physical

The white-thighed surili are made up of a common surili build, ranging from around 41–69 cm tall and weighing 5–6.7 kg. Their slender build is covered with a brown-grey fur coat on their backs, with white fur covering their bellies and dark fur on their head. They are known for the white fur on the outsides of their thighs (giving them their name). Additionally, there tails – typically covered in dark fur – can extend roughly 58–85 cm. Compared to adults, infants are born with very light fur with crosses of dark fur along their arms and back.

Habitat

As an

arboreal Arboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally, but others are exclusively arboreal. The habitats pose nu ...

species, ''P. siamensis'' live in subtropical/tropical forest environments. They have been found to occupy moist lowland or swamp areas. In fact, they can even be inhabitants of terrestrial environments; for example, rural gardens. They can be located mainly on the Malay Peninsula, but are also found in Sumatra, as well as some parts of Thailand.

Social organization

The white-thighed surili live in small unimale-multifemale groups. After mating, females give birth to single infants to which the group of females care for. Due to their arboreal lifestyle, reliance on detection of predators is vital. Male group members are able to call or display a distraction for predators to protect group members. Furthermore, this predator avoidance strategy is shown to be more effective with smaller groups.

Taxonomy

''P. siamensis'' is a member of old world monkeys. ''P. siamensis'' itself contains four subspecies: ''siamensis, cana, paenulata'', and ''rhionis''. Research suggests the white-thighed surili includes '' P. natunae'' (Natuna Island surili) as a subspecies; however both have been considered subspecies of '' P. femoralis'' (Banded surili). Alternatively, research suggests three species are endemic to Malaysia: ''P. siamensis'', '' P. femoralis'' and ''P.'' ''robinsoni'' (Robinson's Banded langur). Through mitochondria DNA analysis, these three species are split into two separate clades: ''P. femoralis'' on its own, ''P. robinsoni'' and ''P. siamensis'' in the other. This was due to the sharing of unique nucleotides between ''P. robinsoni'' and ''P. siamensis''. There continues to be ongoing evolution of Robinson's banded langur and the white-thighed surili. Research suggests that ''P. femoralis'' was the basal lineage of ''

Presbytis The surilis are a group of Old World monkeys in the genus ''Presbytis''. They live in the Thai-Malay Peninsula, on Sumatra, Borneo, Java and smaller nearby islands. Besides surili, the common names for the monkeys in the genus also sometimes use ...

'' in peninsular Malaysia. It was hypothesized that ''P. femoralis'' diverged to form ''P. robinsoni'' and ''P. siamensis.'' The movement of ''P. femoralis'' to the Malaysian peninsula created the allopatric distribution. Further dispersal on the peninsula itself resulted in the divergence of ''P. robinsoni'' and ''P. siamensis'' through

allopatric speciation Allopatric speciation () – also referred to as geographic speciation, vicariant speciation, or its earlier name the dumbbell model – is a mode of speciation that occurs when biological populations become geographically isolated from ...

. Overall, the

taxonomy Taxonomy is the practice and science of categorization or classification. A taxonomy (or taxonomical classification) is a scheme of classification, especially a hierarchical classification, in which things are organized into groups or types. ...

is constantly evolving and in need of continuing research.Brandon-Jones, D., Eudey, A. A., Geissmann, T., Groves, C. P., Melnick, D. J., Morales, J. C., Shekelle, M. and Stewart, C.-B. 2004. ''Asian primate classification.'' International Journal of Primatology 25(1): 97–164.

Threats

According to the

IUCN Red List The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is the world's most comprehensive inventory of the global conservation status of biol ...

, the current status of the white-thighed surili is

near threatened A near-threatened species is a species which has been categorized as "Near Threatened" (NT) by the International Union for Conservation of Nature as that may be vulnerable to endangerment in the near future, but it does not currently qualify f ...

. Researchers say several ''Presbytis'' species are affected by logging activities, although not all of them are recognized on the IUCN red list.

Conservation Conservation is the preservation or efficient use of resources, or the conservation of various quantities under physical laws. Conservation may also refer to: Environment and natural resources * Nature conservation, the protection and managem ...

efforts for non-human primates - such as the white-thighed surili - are valued significantly. This species is seen in the public's eye as a value of science, genetics, forest sustainability, aesthetic, tourism, and a symbol of heritage. Researchers suggest continuing to familiarize the public with primate conservation concerns to enhance the willingness of participate in conservation efforts. In addition, only 30% of the forested area on the Malaysian Peninsula is legally protected from resource extraction, leaving 70% of forests vulnerable. More research on abundance, ecology and behavioural biology of the white-thighed surili is vital to creating better conservation management plans. An alternative threat to this species has nothing to do with logging. Sometimes these primates may be kept as pets or used in the entertainment industry. Currently this species is listed under Appendix II of the Convention on International Trade in Endangered Species (

CITES CITES (shorter name for the Convention on International Trade in Endangered Species of Wild Fauna and Flora, also known as the Washington Convention) is a multilateral treaty to protect endangered plants and animals from the threats of interna ...

) to protect them from this. Moreover, education the public on illegal trade of primates as pets may combat the demand for the industry.

References

{{Taxonbar, from=Q1365651 white-thighed surili Primates of Indonesia Mammals of Malaysia Mammals of Thailand Fauna of Sumatra Near threatened animals Near threatened biota of Asia white-thighed surili Taxonomy articles created by Polbot