The Guinness Book of World Records has recognized a lake as the largest in the world, but the water dried up millions of years ago.
The Parathetys were once covered the present-day Black and Caspian Seas and covered parts of the surrounding European and Asian countries: Kazakhstan, Georgia, Azerbaijan, Romania, Hungary and Serbia.
At its largest, scientists suspect that Paratethys covered about 1.08 million square kilometers.
But the country also went through several periods of desiccation between 7.65 and 7.9 million years ago, eventually shrinking its borders.
And when it reconnected with the Mediterranean Sea between 6.7 and 6.9 million years ago, it was no longer an independent lake.
The new world record is based on a 2021 study that mapped the megalake's historic boundaries and volume.
The Megalake Paratethys once covered the area now occupied by the Black and Caspian Seas. Some of the only surviving evidence of its existence can be found in these cliffs overlooking the Black Sea
These ratios are published in the magazine Scientific reports.
Part of the reason for the delay was that the lake dried up long ago.
But thanks to advanced geological survey instruments, it took its rightful place in the world record books this month.
The Parathetys were home to unique wildlife, including giant elephants, small whales, and rich communities of single-celled organisms that formed the base of the food chain.
Cycles of drying and refilling left their mark on the rocks around the lake. By analyzing the magnetic signature in these rocks, scientists were able to propose a timeline for the lake's rise and fall.
The Parathetys had a tumultuous history, thanks to the region's actively shifting continental plates.
It initially formed as a sea some 34 million years ago, stretching from the Balkans to Kazakhstan and Turkmenistan, overlapping the modern-day coasts of both sides.
The Parathetys once included the Black Sea and the Caspian Sea. It also covered much of modern-day Georgia, Azerbaijan, Hungary, Romania and Serbia
About 11 million years ago, the melting of plates in the Earth's crust led to the formation of the Central European mountain ranges: the Balkans, the Alps and the Carpathians.
These changes cut off the Paratethys from the rest of the open ocean, turning it from a sea into a lake.
For millions of years, the marine species that were trapped as the mountains rose either adapted or went extinct.
A thriving ecosystem soon developed in the Paratethys.
Riabinini, the smallest baleen whale species in the world, has made its home there. This small mammal feeds by filtering microorganisms from the mud at the bottom of the lake.
And the swamps and lowlands around the megalake were home to the Deinotherium, a huge elephant species whose backward-curved tusks may have been used to dig up food.
Unique wildlife has made its home in and around the Eurasian megalake Parathetys. But a series of drying events devastated these communities, and it eventually came into contact with the open ocean again
Between 9.75 and 7.65 million years ago, a series of desiccations caused the lake to lose more than two-thirds of its surface area and a third of its volume. In some places the water level dropped by 250 meters (820 feet).
These fluctuations killed much of the wildlife in the lake. When the Parathetys lost water, the salt concentration rose too much for the residents to adapt.
The timeline of these events is recorded in the rock itself, and scientists can read this data using a technique known as magnetostratigraphy.
Every 100,000 to 1 million years, Earth's magnetic polarity reverses. When each of these events occurred, it left its mark in volcanic rock that hardened with the signature of the current direction.
So if there is a rock whose orientation corresponds to a known polarity reversal, then the surrounding soil and rock can be assumed to be from the same period.
By comparing samples from the areas around the lake with the dates of these reversals, scientists were able to reconstruct the dimensions of the Parathetys.
About 6.7 to 6.9 million years ago, after one of these drying cycles, the Parathetys replenished so much that they reconnected with the Mediterranean Sea.
At this point it ceased to be a separate body of water and lost its status as a lake.
But it still qualified as the largest lake the world has ever seen, cementing its place in the Guinness Book of World Records.