Giant sloths were a thing

Correct, yet these were not "a thing" 500 years ago, not even 5000,try double that and then then "maybe"

The point in the parent comment was not about the literal number 500 but rather about a point in time before humans altered the megafauna

It's actually pretty clear from new imagery the Amazon was significantly deforested and farmed before European diseases wiped out the natives.

And before that, the extinctions mammoths and mastadons (by humans) led to a lot of tree cover that was grassland when the grazers kept the forests in check.

area check https://en.wikipedia.org/wiki/Amazon_rainforest

the amazing, Amazon Basin, is far, far larger than any previous human terraculture eh?

There was an interesting discussion on HN not too long ago (1-3 months?), that we have been wrong about human stress on mammoths etc. We should find it. As usual we learn neat things on HN.