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A reappraisal of the zoogesaphy and systematics of Asian colobines demonstrates marked discontinuities in their distribution. The Bornean proboscis mqnkTy is sepgated by S s a t r a from its sole congener on the Mentawai Islands. &&Gpecies have a discontinuous distribution at the range limit of the As@ Col$inz The existence in the Himala as of some disjunct relatives of the south Ind& S e n e j o h n i i , has one subspecies in southe2India and another in north Vietnam. A closely related Vietnamese leaf m z k e y is a subspecies of the otherwise Indonesian X~u r a~t s~h~u z t a is disjunct between west JLva, northern S u z t r a and northern Bsmeo. The Menswai Islands P. poha'ani is closely related. Biogeographic parallels imply a common cause and previous continuity across the mtervening areas. The only wholly compatible explanation is that the disjunct areas done retained adequate moisture and temperature to support their endemic biota during a cool d r s h t . That not only genera, but species are disjunct, indicates such conditions prevailed recently, and are probably attributable to the Pleistocene glaciations. The supposition that its maritime climate shielded Assan rain@& from the glaci2drought Gown to have partially defossted Africa a 3 SouthAmerica, is inapplicable to the Indian subcontinent, and ignores the climatic effects2 the emergence of the S s d a and the Sahul s h z e s . Such known influences, the distaution of drought indicator plants, foqil plants and fosgd mammals, grassland birds and freshwater fish, and the anatomical specializ&ons of Nasalis confirm the instability of the Asian environment. Theabsence of endemic representatives of c e s n primates in north Sumatra implFs the occurrence of two cold droshts. Available evidence appears to correlate the deforessons with the abrupt curtailment of glacial Stages 7 and 5, at about 190 000 years BP and about 80000 years BP. The greater significance of cx9atic than topographical barriers in delineating the Oriental zoogqsaphic region, and a rapid speciation rate, is implied. Morphological change is evidently generated by geographic dispersal, rather'than geographic isolation.01996 The Linnean Society of London ADDITIONAL KEY WORDS: -biogeographydispersalglaciation -Pleistocenerainforestfauna, has obscured a wider disjunction in w r;-y ich for example, the h o o d m k

With the sakis (Pithecia) and the bearded sakis (Chiropotes), the uakaris (Cacajao) constitute the cebid subfamily, Pitheciinae. The most recent revision recognized six Cacajao subspecies in two species, confined to the Amazon basin. Before 1970 most field information derived from 19th century travellers. Studies still lag behind those of other cebid genera. This paper summarises the known ecology of Cacajao, and identifies future research and conservation priorities. The relevance of Pleistocene refugia and metachromism in analysing its biogeography is discussed. Range size remains obscure but, with the exception of C. c. calvus, may be extensive, as all other subspecies appear to migrate in the dry season from flooded riverine forest to terra firme. Observed group size ranges from 5 to 50, indicating the operation of a fission-fusion society. Social organization appears to be multi-male and non-hierarchical. This accords with the minimal sexual dimorphism. The highly developed canines function primarily as fruit openers. Cacajao is a dietary specialist on hard-shelled fruit, and appears unique among Amazonian cebids in its dependence (at least seasonally) on riverine forests. Hunting may be a problem locally, but local taboos sometimes offer protection. They appear vulnerable to habitat disturbance. On the Rio Negro, the range of C. m. melanocephalus appears to have greatly diminished. To ensure protection of viable populations, the inferred dietary dependence on seasonal migration may require accommodation. Research priorities include the status, habitat preference, diet and social ecology of all taxa except C. c. calvus. A more complete knowledge of the biogeography of the genus would be valuable.

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