Most mammoths went extinct 12,000 years ago, but some stayed around on. Moving glacier carved out prairie pothole region in america. (opening on. Clovis: first human inhabitants in north america, defined by clovis point spears. In favor of overkill: arrival of clovis coincides with extinction of at least 17 megafauna genera, some well-documented kill sites, evidence of overhunting causing extinction on islands, moas. Against overkill: evidence is sparse, continents are not small islands, animals have room to avoid people, clovis may not have been the first in north america, lots of extinctions 12,000 years ago in areas devoid of clovis. In favor of climate debate: extinctions coincide with younger dryas, 12,800 to 11,500 years ago, melting ice likely altered ocean currents and reversed warming. Against climate debate: doesn"t hold for a place like australia where the climate doesn"t change much, climatic shifts no worse than previous ones.