Until recently, scientists believed that the mega-swamp dried up more than 10 million years ago, before the Amazon River reversed course. During most of the Miocene, this river flowed from east to west, opposite to its present direction. The giant animals disappeared when the waters of Pebas receded.
While investigating sediments associated with vertebrate fossils from two paleontological sites on the Acre and Purus Rivers, Marcos César Bissaro Júnior, a biologist affiliated with the University of São Paulo's Ribeirão Preto School of Philosophy, Science and Letters (FFCLRP-USP) in Brazil, obtained datings of 8.5 million years with a margin of error of plus or minus 500,000 million years.
Evidence - Amazon - Direction - Years - Andes
There is evidence that the Amazon was already running in its present direction 8.5 million years ago, draining from the Peruvian Andes into the Atlantic Ocean. By then, the Pebas system must have no longer resembled the magnificent wetlands of old. Rather, the system resembled a floodplain similar to the present-day Brazilian Pantanal. This is the view of Annie Schmaltz Hsiou, a professor in the Biology Department at FFCLRP-USP and supervisor of Bissaro Júnior's research, which is described in a recently published article in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.
The study was supported by São Paulo Research Foundation...
(Excerpt) Read more at: ScienceDaily