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São Paulo – The country of the giants. This is the best definition for Lake Pebas, the megapantbad that existed in the western Amazon during the Miocene, a period that stretched from 23 million to 5.3 million years ago.
Pebas was home to the largest alligator and largest known gharial crocodilian, more than 10 meters long, and the largest turtle, whose hull is 3.5 meters in diameter.
Traces of this ancient biome are spread over more than one million square kilometers, spread between Bolivia, Acre, the western Amazon, Peru, Colombia and Venezuela. . The first dating, done in Venezuela, shows that Lake Pebas existed 18 million years ago. However, it was thought that the megaphanthbad would have dried up more than 10 million years ago, before reversing the course of the Amazon River which, in most of the Miocene, was going from there. west, so in the opposite direction to the current price. With the depletion of the Pebas, the large animals have disappeared.
8.5 million years ago, signs that the Amazon was already running in the current direction, ranging from the Peruvian Andes to the Atlantic. To this day, Pebas should no longer remember the beautiful marsh today. This should look like a floodplain, like the Pantbad of Mato Grosso. It is the opinion of Annie Schmaltz Hsiou, Professor in the Department of Biology of the FFCLRP-USP and Supervisor of the works of Bissaro Júnior, whose results were published in the journal Palaeogeography, Palaeoclimatology, Paleoecology .
The study is supported by the Amparo Foundation. the research of the State of São Paulo (Fapesp) and the National Council for Scientific and Technological Development (CNPq). Participants included researchers from the Federal University of Santa Maria, the Natural Science Museum of the Zoobotanic Foundation of Rio Grande do Sul, the Paulista State University (Unesp), the University of Santa Federal University of Acre and Boise State University in the United States
the name of the Pebas system to the badociation of recordings of various formations geological conditions existing in the western part of the Amazon. These are the Pebas and Fitzcarrald teams in Peru and Brazil, the Solimões formation in Brazil, the Urumaco and Socorro formations in Venezuela, the La Venta formation in Colombia and Quebrada Honda in Brazil. Bolivia.
"Although the formation of Solimões is one of the stratigraphic units of the Neogene period with better fossil samples from northern South America, the badumptions about the age of deposit on Brazilian territory rested largely on indirect methods, "said Bissaro Júnior
The absence of absolute age hinders finer interpretations of palaeoenvironments and palaeoecology of the faunal badociations that are found there and does not allow answer some important fundamental questions, as if these layers had been deposited before the formation of the proto-Amazon or when they had already formed it. "
The first fossils of the region were discovered in the 1980s
Bi logo Bissaro junior shows in his work the first geochronology (for zircon mineral samples) of the Solimões formation.The samples were taken from two of the most well-sampled palaeontological sites in the region, in Niterói, Rio Acre (Senador Guiomar) and Talismã, in the Purus River (municipality of Manuel Urbano).
found, from the 1980s, many Miocene fossils, among crocodilians, fish, rodents, turtles, birds and xenarthropes (terrestrial sloths) .Talisman, from the late 1980s, Miocene remains of crocodilians, snakes, extinct rodents, primates, sloths and ungulates of South America (Litoptera) were discovered
Due to the dating, Bissaro Junior discovered that ro The Niterói site has, as a maximum age of deposition, about 8.5 million years and the Talismã rocks about 10.9 million years ago.
"On the basis of differences, faunísticas and maximum age differences between two localities suggest that Talismã is older than Niterói, but we emphasize the need for new absolute dates to verify this hypothesis, as well as efforts to dating of other sites of the Formation of Solimões ", said Bissaro Júnior.
Depletion of Pebas
The formation of Pebas Lake was due to the uprising of the lands of the Amazon protobacy. This was due to the rise of the Andes, which accelerated compared to 20 million years ago. At that time, the western Amazon was bathed by the Amazon Basins (which were heading to the Caribbean) and the Magdalena River in Colombia. The rise of the Andes, in present-day Peru and Colombia, ended up interrupting the flow of water to the Pacific, which eventually settled at the height of the western Amazon, giving birth to the megapantiano
But the Andes continued to rise. The continuous uprising of Amazonian lands has had two effects. The Proto-Amazon, formerly impounded on Lake Pebas, has reversed its course to become the majestic river we know. Throughout this process, the waters of the mega-shanty town of Pebas were emptied.
The former wetland would become a floodplain, full of huge animals, which still existed 8.5 million years ago, according to new dates of Bissaro Júnior. Finally, unstoppable geological forces eventually drained the waters of what was left of lagoons and temporary lakes in the western Amazon. It was the end of Pebas and its fauna.
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