Vietnam Primate Conservation Status Review 2002 - Hoang Lien ...

5. Snub-nosed monkeys
5.0 An introduction to the snub-nosed monkeys
(genus: Rhinopithecus)
5.0.1 Taxonomy
5 SNUB-NOSED MONKEYS
The south-east Asian colobine genera: Pygathrix, Rhinopithecus, Nasalis and Simias form the “Odd-
Nosed Group” and possess many unusual characteristics of the integument and a high intermembral
index. But whether this is more than an informal group is unclear (Groves, 2001).
The relationship between Rhinopithecus and Pygathrix is disputed. Indeed, the two genera share
some characteristics such as the presence of small flaps of skin on the upper margins of the nostrils,
the reduction of the nasal bones and a similarity in limb proportions (Groves, 1970; Oates et al.,
1994). Following these observations, several authors considered Rhinopithecus as a sub-genus of
Pygathrix (Groves, 1970; Brandon-Jones, 1984; P. Napier, 1985; Corbet & Hill, 1992; Davies & Oates,
1994; Rowe, 1996), but Jablonski & Peng (1993) analysed Pygathrix and Rhinopithecus and argued
strongly for their recognition as a full genus which is now widely accepted (Eudey, 1996/1997;
Hilton-Taylor, 2000; Groves, 2001; see also 2.3).
The genus Rhinopithecus is commonly named “snub-nosed monkeys”. The genus comprises four
species, three of them occur in the mountains of southern China, and one, the Tonkin snub-nosed
monkey (Rhinopithecus avunculus) is endemic to Vietnam.
5.0.2 Morphology, ecology and behaviour
Among “Odd-Nosed Monkeys”, Rhinopithecus has a distinctive nasal anatomy. The lateral crura of
the greater alar cartilages is prominent, the nasal bones are abbreviated or absent and the bony
nasal septum and septal cartilage are abbreviated in the rostrum. These features are associated with
complex motifs of the mid-facial bony structures. In addition, the interorbital distance is relatively
wider and the muzzle more shortened than most colobines, exhibiting a net concave mid-facial profile
(Jablonski, 1998). The purpose of this anatomical feature is unclear but it’s possible that this could
have the function of warming and the humidifying of inhaled air in a dry and cold mountain habitat.
The species of Rhinopithecus, in particular the Chinese species, are also distinguished by a series of
gnathic and dental charcteristics (Jablonski, 1998).
The Tonkin snub-nosed monkey is Vietnam’s largest primate. Compared with other Rhinopithecus
taxa, R. avunculus has a different constitution and different habits (Ren et al., 1998). For instance, R.
avunculus is more slender, with elongated digits, and slightly less sexual dimorphism.
The diet of the Rhinopithecus species seems to consist largely of leaves, grass, lichens, bamboo shots,
buds, and fruits. But there is a differentiation within the species (Bleisch et al., 1998).
The diet of R. avunculus is composed mainly of fruit and leaves. The first studies of stomach contents
suggested that the species was mostly folivorous, with a strong preference for bamboo. Indeed more than
60% of the stomach contents of two females contained bamboo fragments (Ratajszczak et al., 1992).
However, the later surveys tend to suggest a more frugivorous diet (Pham Nhat, 1994b; Boonratana & Le
Xuan Canh, 1994). This second hypothesis is supported by further studies of stomach contents and field
surveys. Boonratana & Le Xuan Canh (1994), using scan sampling from 34 feeding observations, estimated
that 47% of its diet constituted whole, unripe fruit, 15% seeds of ripe fruits and 38% of young leaves and
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