"Mammals went extinct as humans expanded, and they went extinct in areas where the climate was stable but humans were new." That squares with something I think

"Mammals went extinct as humans expanded, and they went extinct in areas where the climate was stable but humans were new." That squares with something I think I read in Guns, Germs, and, Steel, which was that the reason African megafauna like elephants, lions, etc. survived to this day is that they co-evolved alongside humans to the point that they knew to be afraid of the puny little buggers. Meanwhile a 2-ton giant marsupial in Australia had no reason to fear and evade the new bipedal neighbors, or so it thought...