Geissmann, T. (2003). Circumfacial marking in siamangs and evolution of the face ring in the Hylobatidae. International Journal of Primatology 24: 143-158.
Institute of Zoology, Tierärztliche Hochschule Hannover, Germany
Key words: Symphalangus syndactylus;
siamang; gibbon; face ring; fur coloration; evolution
Abstract: The occurrence of a white brow band in siamangs is documented for the first time. The characteristic occurs in 4.4% of the 250 siamangs examined for this study. Among adult siamangs, the characteristic was found more often in females than in males (11.3% of 71 females vs. 1.4% of 73 males, respectively). In a particular family lineage of captive siamangs (not included in the numbers above), the characteristic was unusually frequent (42.9% of 14). The trait appears to be inherited (possibly an autosomal dominant inheritance). Additional white markings occur in at least one of the study animals on hands, feet, and in a corona above the ears. In contrast to other studies, the results of the present paper suggest that the presence of white facial markings, and possibly also of white hands and feet and of a bright corona are primitive gibbon traits. In addition, some degree of sexual dichromatism in the circumfacial markings appears to have occurred in the common ancestor of all gibbons.
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