What caused the Pleistocene Mass Extinction?

[tigerluver]

@brotherbear , I agree, that's what makes the situation so intriguing. A. simus' hypercarnivory has been refuted multiple times now and it is now considered an omnivore. As an omnivore, it must have had a dietary plasticity not too far off as the modern bears. So what doomed A. simus but not our modern American bears? 

In the case of A. simus, I don't think it was humans as hunting it even with a spear would not be easy and there was no good reason to do so. Hunting the prey of A. simus should not have been a major problem as well, as it was omnivorous. 

My gut tells me size is one factor, as there was a floral turnover due to the climate change event. If I remember correctly, weren't prehistoric American brown bears a bit smaller than today's? Maybe that's why they survived the energy shortage and A. simus did not. Once the niche of gigantic bear opened up and the Earth recovered, modern bears began putting on size and mass. Reply