The linked article is from 2020, which seems to be when researchers started publishing more about it, not when it was discovered. Modern re-discovery seems to date back to at least the mid-19th century by Italo-Venezuelan geographer Agostino Codazzi, and then multiple other mentioned people in the 20th century. https://www.discovermagazine.com/amazon-rock-art-could-depict-millennia-old-megafauna-43686 The delay for research to catch up can be explained by the presence in the region of the FARC, the Columbian Marxist–Leninist guerrilla group, which disarmed itself in 2017 after a peace deal and 53 years of activity. https://www.sciencedirect.com/science/article/pii/S0278416524000448#b0130