Conclusions

Theories that have been advanced to account for the extinction of the late Pleistocene fauna can be divided into two basic types: those that attribute extinction to the agency of man (Martin 1967, 1973, 1974; Mosimann and Martin 1975) and those that invoke the effects of climatic change (Guilday 1967, Slaughter 1967, Dreimanis 1968). Importantly, the foundation of each is presumed temporal correlation. For example, Long and Martin observe, "the apparently synchronous loss of the Shasta ground sloth with the arrival of big game hunters in Arizona . . . [is] in accord with the [human overkill] model" (Long and Martin 1974:650).

The correlation between the appearance of Pleistocene hunters, the development of Holocene climates, and the disappearance of the Pleistocene fauna remains equivocal. Some archaeologists have questioned the apparent late Pleistocene arrival of man (MacNeish 1976, 1979; Bryan 1978; Byran et al. 1978). The timing of the major late and postglacial environmental changes has proven to be more complex than previously known (e.g., Wright 1981). And, as has been demonstrated here, the radiocarbon record for the relevant fauna leaves many questions unanswered.

The demonstration from the radiocarbon record that the extinctions were synchronous or gradual and successive will not itself resolve the nearly 200-year-old problem of the extinction of the late Pleistocene megafauna. The evidence from the radiocarbon record will have to be coupled with evidence relating to population dynamics, change, and collapse, and the whole embedded in a viable and testable theory. That will ultimately determine whether there was a wave of synchronous extinctions or whether one genus predeceased another by hundreds or even thousands of years.