Now let me get this straight. It is said that the Amazonian rainforest contains plant and animal species found nowhere else in the world (save the rainforest). If the rainforest is only 2,000-3,000 years old is that enough time to evolve these unique species?
I would imagine that the 2000 to 3000 years ago (I wonder if they meant 3000 years BC, since the cores go back 6000 years), the rainforests were just in a different place. Say SW North America which is now desert. As the climate changes in various places, the species (plants, animals, birds, etc.) just follow.
I recall reading some National Geographic article years ago. One article was about some animal that is being more and more rare in the U.S. due to Global Warming, and something needs to be done, etc. (The article did bury the fact that they are just heading north into Canada).
In the same mag, another article was shouting with joy the sighting of some rare bird, the first time it has been seen in the states for 200 years, and people from all over were coming to see it. (It’s usual range was a few hundred miles south of the border in Mexico. No mention of global warming).
That part of the article was very unclear. The extent of the rainforest ebbs and flows with climactic conditions. The rainforest in Bolivia has been there for a few thousand years but the rainforest as a whole has been there for millions of years.
The rainforest/jungle I that area is young but that does not imply there was no existing rainforest or jungle species in adjacent regions.
In short, the jungle encroached when rainfall permitted it, and birds and other animals followed the advance of the plant growth.