The current issue of the Proceedings of the National Academy of Science is chock-full of fascinating stuff. First, there’s this:
Asynchronous extinction of late Quaternary sloths on continents and islands
Whatever the cause, it is extraordinary that dozens of genera of large mammals became extinct during the late Quaternary throughout the Western Hemisphere, including 90% of the genera of the xenarthran suborder Phyllophaga (sloths). Radiocarbon dates directly on dung, bones, or other tissue of extinct sloths place their ”last appearance” datum at ~11,000 radiocarbon years before present (yr BP) or slightly less in North America, 10,500 yr BP in South America, and 4,400 yr BP on West Indian islands. This asynchronous situation is not compatible with glacial–interglacial climate change forcing these extinctions, especially given the great elevational, latitudinal, and longitudinal variation of the slothbearing continental sites. Instead, the chronology of last appearance of extinct sloths, whether on continents or islands, more closely tracks the first arrival of people.
This ties nicely into much current thinking in extinction theory, where human predation is increasingly viewed as the main causal element in many waves of species disappearance, dating back even to prehistoric times, as above. For a long time it had been thought that geological events were the cause, and while they undoubtedly played a role, the asynchronous extinction of sloths helps show that there was more to such waves than the odd meteor wiping out at the Yucatan Peninsula.
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