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The country of the giants. This is the best definition of 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 earliest date, made in Venezuela, is that Lake Pebas existed 18 million years ago.
In the meantime, it was thought that the megapanthbad would have dried up more than 10 million years before the reversal of the month. Amazon, which in most of the Miocene was traveled from east to west, so in the opposite direction of the current course.
Survey of the sediments of two paleontological sites of the Acre and Purus rivers, badociated with vertebrate fossils, biologist Marcos César Bissaro Júnior, of the Faculty of Philosophy, Sciences and Letters of Ribeirão The Black University of São Paulo (FFCLRP-USP) has obtained dates of at least 8.5 million years, with a margin of error of 500,000 years for plus or minus.
8.5 million years ago, it seems that the Amazon is already heading in the same direction, going from the Peruvian Andes to the Atlantic. To this day, Pebas should no longer remember the beautiful marsh today. It should look like a floodplain, just like the current swamp 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, Palaeoecology .
The study was funded by 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. "
To answer these questions and others, Bissaro Júnior presents in You are working on the first geochronology (on samples of mineral zircons) of the formation of Solimões The samples were collected in two of the most paleontological sites sampled from the region, at Niterói, in the Acre River (municipality of Senador Guiomar), and at Talismã, in the Purus River (municipality of Manuel Urbano)
found, from the 1980s, many fossils of the Miocene, among crocodilians, fish, rodents, turtles, birds and xenarthropes (terrestrial sloth) In Talisman, from the late 1980s, Miocene remains of crocodilians, snakes, rodents, extinct primates, sloths and ungulates from South America (Litoptera) were discovered
Due to dating, Bissaro Junior discovered that rock hey of the Niterói site have, as maximum age of deposit, 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.
Formation of Pebas Lake was due to the uprising of the lands of the Amazon protobacy, the rise of the Andes, which has accelerated for 20 million years. The western Amazon was bathed by the Amazon Basins (which were heading towards 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
"The problem of dating Pebas has always been to badociate the dates directly to the vertebrate fauna. There are innumerable dates of Rocks where invertebrate fossils have been discovered.Rocks with vertebrates was one of our goals, "said Schmaltz Hsiou.
According to the teacher, the new dates give us an opportunity to suggest that the Pebas system, from the Great Swamp, would have existed between 23 and 10 million years ago. gave birth to the so-called Acre system, the great floodplain that existed between 10 and 7 million years ago, where reptiles still lived, such as Purussaurus and Mourasuchus .
"The Acre system should be a biome similar to that of Venezuela at the same time, consisting of lagoons around the delta of a large river, which would be the proto-Orinoco," said Schmaltz Hsiou.
Rodents are a group of extremely diverse mammals of all continents, with the exception of Antarctica.
"In particular, a group of rodents known scientifically as Caviomorpha arrived on our continent about 41 million years ago, from Africa," did he declare. another author of the article published in Palaeogeography, Palaeoclimatology, Palaeoecology, Leonardo Kerber, Center for Support of Paleontological Research of the Fourth Colony (Cappa) of the Federal University of Santa Maria [19659006] "At that time, known as the Eocene, Africa and South America were already totally separated from at least 1,000 km between the nearest points of the two continents; which would make biogeographic links unworkable to allow terrestrial vertebrates to migrate between two land mbades, while ocean currents have caused ocean dispersion by means of natural floating rafts formed by a group of logs and branches cut by These floating ferries eventually carry small vertebrates, such an event may have favored the crossing of small mammals. eras, such as Platyrrhyni (19459005) Platyrrhyni and small rodents that would give birth to one of the most iconic groups of South American mammals, caviomorphic rodents, "he said. 19659002] According to Kerber, since their arrival on the continent, caviomorphic rodents have experienced a long period of evolution, which has made them extremely diverse. Currently, representatives of this group in Brazil are bullets, cuties, preas, porcupines, thorny rats and capybara, the largest rodent in the world.
"Especially in the Amazon, today there is a great diversity of thorny and porcupine rats or hedgehogs, as well as agate and ball, but in the Miocene, the fauna of the Amazonian region was very different. from the one we can observe today, "said Kerber.
"In recent years, besides the communication of the presence of several fossils of species already known to science, some (19459005) Potamarchus adamiae Pseudopotamarchus villanuevai Pseudopotamarchus villanuevai ] and Ferigolomys pacarana – Dinomyidae ), which have a relationship of kinship with the pacarana, "he said.
Kerber says this in an article to be published soon in the Journal of Vertebrate The paleontology of the species Neoepiblema acreensis a Neoepiblemidic rodent endemic to the Miocene of Brazil which weighed about 120 kilos, was recognized as
"The species was described in 1990 but was considered invalid at the end of the same decade.These records, both of known species and new species, help to understand how life has evolved. in this region, thus showing that biodiversity has evolved and has also been extinct over the last millions of years, "said Kerber
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