Animal and plant life have not evolved much during the relatively short Holocene, but there have been major shifts in the distributions of plants and animals. A number of large animals including mammoths and mastodons, saber-toothed cats like "Smilodon" and "Homotherium", and giant sloths disappeared in the late Pleistocene and early Holocene—especially in North America, where animals that survived elsewhere (including horses and camels) became extinct. This extinction of American megafauna has been blamed by some on the Clovis people, who vanished at the same time, though climatic change or a bolide impact are favored by others.