Most of the large mammals in North America mysteriously became extinct after the arrival of native Americans.
The evidence is overwhelming it was human hunting....
The authour of "Guns, Germs, and Steel" thinks it was and that's one of the greates books I've ever read.
Unlike the large animals of Africa, the ones of North America didn't have humans gradually evolving so they could get used to the idea that humans were a danger to them......they were easy marks.