Paratethys

The Paratethys Sea, also called the Paratethys Ocean or Paratethys realm, was a big shallow inland sea. It 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. It is thought to be 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. This separation was caused by 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, it 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 talk about old fossils and layers of mud from the sea during the Neogene period. Later, scientists added the Oligocene period too.

Scientists learned about this old sea by looking at 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 hard to match the layers of rock from Paratethys with those from other oceans. So, experts who study these rock layers use their own 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 by narrow waterways. This 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. 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 warm water full of many kinds of sea life, including special coral reef areas. Some parts, like where Poland is today, were deep enough for deep-sea life. We know this from well-preserved fossils from the Oligocene-aged Menilite Formation, which include fossils of deep-sea fish and tiny sea organisms. But later changes hurt this 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 deep-sea homes. Surface sea animals also declined because the tiny sea creatures they ate disappeared. Even though it was full of life, this special time only lasted about 3 million years.

Fishes

The Paratethys was separated from other big oceans, so many types of fish changed in new ways to fit their home. These fish were related to fish we see today, but they were special groups that are now gone. For example, small fish called gobies did very well in the Paratethys, with many special kinds known from fossils. 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 in 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. Later groups of fossils show that when the Paratethys became more separated, most smaller deep-water and open-ocean sharks disappeared. But bigger sharks, like the large megalodon and Cosmopolitodus, stayed around.

Marine mammals

The Paratethys was 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. 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, sea mammals developed very thick, heavy bones. This change happened in seals, toothed whales, and baleen whales.