Toward the end of the last ice age, a group of horse species that lived in Alaska shrank in body size over several millennia before going extinct. That finding implicates changing environmental conditions as the stimulus for equine die-offs in the region, one researcher suggests. Some scientists previously proposed that the arrival of human hunters was to blame for the demise of many species of large North American mammals (SN: 12/4/99, p. 360: http://www.sciencenews.org/sn_arc99/12_4_99/bob1.htm).
Caballoid horses, a group of stocky species related to some Eurasian horses, were once common in what is now Alaska. But they, along with 70 percent of North America's large mammal species, disappeared by the end of the last ice age, says R. Dale Guthrie of the University of Alaska in Fairbanks.