North America, in particular, is an example of a place where humans speeded the process of climate-caused extinction, in many cases by overkill. Evidence of mammoth kills date from near the first appearance of stone spearheads made by the human Clovis civilization 11,400 years ago. Only mammoths and mastodons have been found with incontrovertible evidence that they were killed by humans in North America, though human artifacts have been found in association with extinct megafauna fossils on all continents, including Africa.
Over a period of, at most, 1,500 years, following the appearance of Clovis-style hunters, camels and horses, rhinos and peccaries, short-faced bears and saber-toothed tigers, as well as the armadillo-like glyptodonts and the giant ground sloths (Megatheriadae), all disappeared from the North American continent.
"Humans and climate change came together at exactly the same time" to lead to these great megafauna extinctions, Barnosky said.
The case in South America is still muddled, he noted, but there, too, human incursions combined with climate change possibly coincided with the departure of large mammals, such as a variety of armadillos and llama- and camel-like animals, in a case similar to that in North America. In Africa, as well, it is unclear why any large mammals went extinct, since humans arose in concert with these animals and, by some arguments, they should have been in balance with one another. There, as in South America, the uncertainty comes from lack of data.
In these fairly recent large-mammal extinctions, Barnosky sees lessons for the future.'"/>