How the world’s largest lake appeared and disappeared

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US, WASHINGTON (ORDO NEWS) — Two new studies show the history of an ancient reservoir that was formed 12 million years ago. It was the largest lake in the world. It stretched from the Eastern Alps to today’s Kazakhstan. And it was inhabited by amazing animals – miniature versions of whales, dolphins and seals.

When lithospheric plates collided 12 million years ago, they not only created new mountains in Central Europe. They formed the largest lake in the world. In this huge reservoir called Paratethys, species appeared that were not found anywhere else, including the smallest whales in the world. Two new studies show how this sea took shape and how changes in the environment gave rise to elephants, giraffes and other mammals that still roam our planet.

To recreate the timeline, paleo-oceanographer Dan Palcu of the University of São Paulo and colleagues gathered information from geological and paleontological sources. When this ancient sea covered a maximum area of ​​2.8 million square kilometers, it stretched from the eastern Alps to today’s Kazakhstan. This is larger than the Mediterranean Sea today, scientists say in Scientific Reports. According to their estimates, this lake once contained 1.77 million cubic kilometers of water, which is 10 times the volume of all fresh and salt lakes combined today.

But due to climatic changes, the lake has significantly decreased in size at least four times over the five million years of its existence. In the period 7.65 – 7.9 million years ago, the water level in the lake dropped by 250 meters. During this longest period of drying up, the lake lost a third of its water and more than two-thirds of its area. Because of this, in its central basin, which coincides in outline with today’s Black Sea, the salinity level has increased sharply. If before the onset of the drying period, the salinity of Paratethys was three times lower than in today’s oceans, then after it it became equal to this level.

Due to these changes, many aquatic species became extinct, including numerous species of unicellular algae and other small free-swimming organisms. Creatures that could survive in salt water, including some molluscs, populated the lake when it began to increase in size again in wetter times, Palchu said.

Paratethys soon became home to a huge variety of molluscs, crustaceans and marine mammals not found anywhere else in the world. Many of the whales, dolphins and seals that lived there were miniature versions of species that inhabited the high seas, said evolutionary biologist Pavel Goldin, who works at the Institute of Zoology. Schmalhausen at the National Academy of Sciences of Ukraine and did not participate in this work. One species, the three-meter Cetotherium riabinina, was one meter shorter than today’s bottlenose dolphin, and is the smallest whale found in sediment. Dwarfism probably helped these animals adapt to the conditions of the shrinking Paratethys, Goldin says.

Climatic changes that caused the lake to shrink have also influenced the evolution of land animals, says Madelaine Böhme, an evolutionary biologist at the University of Tübingen. When the water level dropped, new coastal areas became grasslands, becoming a hotbed of evolution.

Recently Boehme and colleagues studied geological material from western Iran, where sedimentary deposits mimicked long-term climate change. Fossil finds show that in areas north of Paratethys, the ancestors of the modern sheep and goat grazed alongside the primitive antelope. And south of the lake, where western Iran is today, the progenitors of modern giraffes and elephants were found in abundance.

6.25 million to 8.75 million years ago there were four long dry spells, and most likely weather conditions forced these animals to migrate southwest towards Africa, Boehme and her colleagues wrote in Communications Earth & Environment last month. There they evolved, producing a wide variety of animals for which the African savanna is famous today.

And Paratethys was destined for a sadder fate. The lake ceased to exist 6.7 – 6.9 million years ago, when due to erosion in its southwestern part there was an outlet for water. This channel, most likely located under the Aegean Sea, gave rise to a short river, which eventually reached the Mediterranean Sea. But as Palchu says, this massive lake still screamed its last hurray. The water flowing out of it on its way to the sea created an “impressive waterfall”.


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