Geissmann T., 1987: Evolution of facial markings in gibbons (Hylobates spp.). International Journal of Primatology 8: 540 (Abstract only).
Anthropological Institute, University Zürich-Irchel
The different forms of bright facial markings in gibbons are frequently used to assess systematic and phylogenetic relationships between the various species. Siamangs (Hylobates syndactylus) and Kloss gibbons (H. klossii) usually have no facial markings. In siamangs, a very faint face ring may occasionally occur in old age (Haimoff et al., 1982: Folia primatol. 39: 213). Here, I report the occurrence of a white brow-band (similar to those of H. hoolock males and H. agilis females) in a family of siamang, maintained in captivity for the third generation. This characteristic occurs in 3 related females, but is absent from 2 unrelated males and from a further male bred in the colony. The trait therefore seems to be inherited and may be sex-limited. Its presence was first documented at the age of nine months. Additional white markings occur in at least one of these individuals on hands, feet, and in a corona above the ears which darkened with age. This report casts doubt on recent studies identifying the absence of white facial markings in gibbons as a primitive character state. Likewise, the presence or absence of white hands and feet, of a bright corona, and even of sexual dimorphism in colouration all have to be reconsidered with respect of their evolutionary history.
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