ABSTRACT
THE FAuN A oF a region changes in course of time in response to climatic oscillations, there is emergence and spread of new species, and the dying out of others. Some genera and species are more useful age-indicators than others, either on account of being subject to rapid evolutionary change (eg elephants), or on account of the speed and extent of their migrations ( eg deer). Among mammalia, the most useful groups for correlating Pleistocene deposits are: elephants, rhinoceroses, bears, hyenas, certain small mammals (microtine rodents, shrews, etc), pigs, deer and bovids. The extent to which R.3 dating by means of Pleistocene mammalia approaches 'absolute' (in the sense of synchronic) dating, depends on the speed with which the 'dating' species migrated. Where unchecked the larger mammals spread at the rate of about r,ooo kilometres in a century, but with small mammals the rate is slower (Kurten, 1957). Probably the main limitation to correlating deposits across the world by means of mammalia is the fact that some forms do not migrate far, and that even the most widespread species fail to cross certain boundaries.
