Caspian Sea
The Caspian has characteristics common to both seas and lakes. It is often listed as the world's largest lake, although it is not a freshwater lake. It contains about 3.5 times more water, by volume, than all five of North America's Great Lakes combined. The Caspian was once part of the Tethys Ocean, but became landlocked about 5.5 million years ago due to plate tectonics. The Volga River (about 80% of the inflow) and the Ural River discharge into the Caspian Sea, but it has no natural outflow other than by evaporation. Thus the Caspian ecosystem is a closed basin, with its own sea level history that is independent of the eustatic level of the world's oceans.
Caspian tiger
Its former distribution can be approximated by examining the distribution of ungulates in the region. Wild boar was the numerically dominant ungulate occurring in forested habitats, along watercourses, in reed beds and in thickets of the Caspian and Aral Seas. Where watercourses penetrated deep into desert areas, suitable wild pig and tiger habitat was often linear, only a few kilometers wide at most. Red and roe deer occurred in forests around the Black Sea to the western side and around the southern side of the Caspian Sea in a narrow belt of forest cover. Roe deer occurred in forested areas south of Lake Balkash. Bactrian deer occurred in the narrow belt of forest habitat on the southern border of the Aral Sea, and southward along the Syr-Darya and Amu-Darya rivers.