It is discoveries like this one that make me think that the estimates of human population in the ancient world are extremely low.
For instance the large cities in the Incan empire that are being discovered with Satellites.
It seems that the human population exploded rapidly at the end of the last ice age.
I had a class back when I was young and pretty that had as one of its texts, "The Invasion of America", a predictably anti-colonialist screed. One of the claims was that the population of North America (as was the case in Central America) had hit a height before 1492-ish that wouldn't be reached again until the 19th century or early 20th century. Obviously the culprit (if there was one) would have been inadvertently introduced diseases.
Interestingly enough, in a completely different class we learned that the Mayans had I think four different population peaks, with the final one in the early 16th century, just as Cortez arrived. Unless one attributes the earlier ones to a similar introduction of diseases by ocean-crossers -- which could help clarify where some of the ancient pandemics in Eurasia came from -- one is stuck with the 100 percent natural climate changes that continue to this day.