Paratethys

The Paratethys Sea, also called the Paratethys Ocean or Paratethys realm, was a vast shallow inland sea that covered much of mainland Europe and parts of western Asia during the middle to late Cenozoic. It existed from the late Paleogene to the late Neogene and is considered the largest inland sea ever known. At its biggest, it stretched from north of the Alps across Central Europe to the Aral Sea in Central Asia.

Paratethys formed about 34 million years ago at the start of the Oligocene epoch. This happened when the northern part of the Tethys Ocean became separated from the Mediterranean area because of the formation of the Alps, Carpathians, Dinarides, Taurus, and Elburz mountains. Over time, Paratethys sometimes connected back to the Tethys or its successors, like the Mediterranean Sea or the Indian Ocean, but later became trapped and turned into a huge lake.

From the Pliocene epoch onward, about 5 million years ago, Paratethys grew shallower and shallower. Today, the Black Sea, Caspian Sea, and Aral Sea are what remain of this ancient sea.

Name and research

The name Paratethys was first used by Vladimir Laskarev in 1924. He used it to describe fossils and layers of sediment from the sea during the Neogene period. Later, scientists added the Oligocene period to this definition too.

Scientists learned about this ancient sea by studying the animals that lived in it, like mollusks, fish, and tiny creatures called ostracods. When parts of the Paratethys were cut off from other oceans, special groups of animals developed there. This makes it tricky to match the layers of rock from Paratethys with those from other oceans, because the animals evolved in their own way. So, experts who study layers of rock from Paratethys use their own special time steps, which are different from the main timeline used for the whole world.

Palaeogeographic evolution

Paratethys was special because of where it was located: it had deep basins that formed long ago during the Late Jurassic period. These basins were linked to each other and to the global ocean by narrow waterways, which often limited water flow and caused low oxygen levels in the water.

Paratethys covered a large area in Central Europe and western Asia. It included places like the Molasse basin north of the Alps, the Vienna Basin, the Outer Carpathian Basin, the Pannonian Basin, and areas near the Black Sea, Caspian Sea, and Aral Sea.

During a time of big climate change and mountain building, Paratethys became separated from the global ocean. This caused the water to have very low oxygen levels for many millions of years. Later, better connections with the ocean improved water flow and oxygen levels.

After this, Paratethys had open waters with many sea creatures like sharks and corals. But soon after, rising mountains and falling sea levels caused salt to build up in the water. Thick layers of salt formed in many places, which we still mine today.

About 12 million years ago, Paratethys changed into a huge lake covering over 2.8 million square kilometers. This lake had many unique animals, including small versions of whales and dolphins. Sadly, changes in the environment later caused many of these animals to disappear.

Finally, during a time when parts of the Mediterranean dried up, water from Paratethys flowed into the Mediterranean. Later, Paratethys split into smaller seas, and today only the Black Sea, Caspian Sea, and Aral Sea remain.

Paleoecology

During the Middle Miocene Climatic Optimum, the Paratethys had a warm to very warm water world with many different kinds of sea life and lots of special species, including coral reef areas. Some parts of the Paratethys, over where Poland is today, were deep enough to support special deep-sea life. We know about this from a very well-preserved set of fossils from the Oligocene-aged Menilite Formation, which includes fossils of deep-sea fish and special layers made by tiny sea organisms. But later changes in the environment hurt this rich sea life a lot. The coral reefs disappeared when the water got colder during the Middle Miocene disruption, and changes in water flow and lack of oxygen destroyed the deep-sea homes. Surface sea animals also declined because tiny sea creatures they ate disappeared. Even though it was full of life, this special time for sea creatures only lasted about 3 million years.

Fishes

Because the Paratethys was separated from other big oceans, many types of fish changed and grew in new ways to fit their new home. These fish were closely related to fish we see today, but they were special groups that are now gone. For example, a group of small fish called gobies did very well in the Paratethys, with many special kinds known from fossils and tiny ear bones of fish. The many kinds of modern herrings, shad, and similar fish also grew a lot in the Paratethys, and we know about many from fossils.

Links from the Paratethys to the Mediterranean Sea let many sharks and rays move into the Paratethys Sea by the early Miocene. A group of deep-water sharks from Slovakia that lived in the Miocene seems to have been small and not very many, perhaps because their home was not very healthy. Later groups of fossils show that when the Paratethys became more separated in the middle Miocene, most smaller deep-water and open-ocean sharks disappeared. But bigger sharks, like the large megalodon and Cosmopolitodus, stayed around, probably because they could eat marine mammals that were common.

Marine mammals

The Paratethys was also home to many kinds of sea mammals, including whales and seals. It had several small kinds of baleen whales from a group called Cetotheriidae, like Cetotherium rathkii and Ciuciulea davidi. These are some of the smallest baleen whales known, and it’s thought they might have first lived in the Paratethys. A special group of toothed whales called eurhinodelphinids seems to have entered the Paratethys from the Mediterranean during the middle Miocene, with fossils of the common genus Xiphiacetus found in Austria. Another older toothed whale, Romaleodelphis, also seems to have been special to the Paratethys. Over time, as the Paratethys became saltier because it was separated, sea mammals separately developed very thick, heavy bones. This change happened in seals, toothed whales, and baleen whales, starting in the central Paratethys after a big change in salt levels and then spreading eastward.