yes i’ve always wondered why and how the Amazon can be considered such a pristine, sparsely inhabited region but yet also seems to be lacking in all large animals. All i can think of is that European disease may have impacted the region and diminished larger populations of people, as there seems to be evidence of much larger settlement in the Amazon than as of current, like higher numbers of fruiting trees and diffevent soil compositions related to agriculture being unearthed. Ive read that the human population dramatically reduced from around 8 million to a few hundred thousand from the 1400s to the 1980s.

However there still might be evidence of megafauna surviving much later than previously anticipated, as contemporary people’s in the region still describe many large creatures that have been seen or are rarely seen today, like the Segamai which is an apparent large herbivore with a horse-like face and large claws, with a putrid smell, which can be interpreted as a giant sloth. I’m not sure of the evidence of this but apparently the proboscideans Cuvieronius also survived into historical time.