Paratethys
The Paratethys was a huge, shallow inland sea that covered much of Europe and parts of western Asia during the middle to late Cenozoic, from the late Paleogene to the late Neogene. At its peak it stretched from north of the Alps across Central Europe to the Aral Sea. It formed about 34 million years ago when the northern part of the ancient Tethys Ocean was cut off from the Mediterranean region by the building of mountains like the Alps and Carpathians. Sometimes Paratethys connected again with the Tethys or the Mediterranean, but in the late Miocene it became a mostly isolated, landlocked sea that extended from the eastern Alps to what is now Kazakhstan. From about 5 million years ago it became progressively shallower. Today’s Black Sea, Caspian Sea, and Aral Sea are remnants of the Paratethys.
The name Paratethys was first used in 1924 by Vladimir Laskarev, who originally based it on Neogene fossils. Later, scientists widened the idea to include older rocks as well. The Paratethys had a distinctive, mostly endemic set of animals and plants, especially in its freshwater and brackish areas. This made its fossil record different from other seas, so geologists use their own regional stages when studying it.
Geography and history: Paratethys began as a group of deep basins in what is now Central Europe and western Asia. These basins were connected to the world ocean by narrow, shallow channels, which limited water exchange and often led to low-oxygen conditions in parts of the sea. Over time, tectonic uplift (the same forces that formed the Alps and other mountain belts) reduced connections to the global ocean and helped create long-lasting isolation.
In the earliest part of the Cenozoic, there was a big drop in the global sea level and cooling of the climate, which helped separate Paratethys from the rest of the Tethys Ocean. The eastern part stayed largely anoxic for about 20 million years, acting as a giant carbon sink. In the middle Miocene, a period of flooding called the Badenian Flooding briefly reconnected Paratethys with the global ocean and allowed open-marine life to spread. But later, ongoing mountain building and sea-level drops again isolated Paratethys, causing a major salinity crisis from about 13.8 to 13.4 million years ago. Evaporites like salt and gypsum formed in several basins.
Megawetland to megalake: About 12 million years ago Paratethys largely became a huge megalake, covering more than 2.8 million square kilometers from the eastern Alps to today’s Kazakhstan. Salinity was moderate, around 12–14 parts per thousand. This long-lived megalake hosted unique species found nowhere else, including some microscopic and small marine mammals. In 2023, Guinness World Records called it the largest lake in Earth’s history. A later crisis reduced its unique fish fauna. When parts of the Mediterranean dried up during the Messinian crisis about 6 million years ago, Paratethys water briefly flowed into some Mediterranean basins.
The Pliocene era saw Paratethys break into a few inland seas, such as the Pannonian Sea, with many of these bodies disappearing before the start of the Pleistocene. Today, only the Black Sea, Caspian Sea, and Aral Sea remain as echoes of the old Paratethys.
Biology and fossils: During the middle Miocene, Paratethys supported a warm, biodiverse ecosystem with coral reefs and many endemic species. Some areas in what is now Poland were deep enough to host unique deep-water communities. The Paratethys fossil record shows a distinctive mix of species that evolved separately from those in other oceans, including groups of gobies and various herring-like fish that later spread elsewhere. Sharks and other marine life entered Paratethys from the Mediterranean in the early Miocene, but later isolation reduced deep-water shark diversity. Large sharks such as the megalodon continued to live there, helped by the presence of marine mammals.
Marine mammals were also diverse in Paratethys, including small baleen whales and various toothed whales. As salinity rose with isolation, many marine animals evolved denser bones as an adaptation, a pattern seen in seals and some whales. Some of these bones later spread eastward within the Paratethys region.
In short, Paratethys was a vast, evolving inland sea whose changes in connection, depth, and salinity shaped a unique and now largely lost world of life. Its remnants live on in the Black Sea, Caspian Sea, and Aral Sea.
This page was last edited on 3 February 2026, at 21:03 (CET).