The Caspian tiger was a Panthera tigris tigris population native to eastern Turkey, northern Iran, Mesopotamia, the Caucasus around the Caspian Sea, Central Asia to northern Afghanistan, and the Xinjiang region in western China. Until the Middle Ages, it was also present in Ukraine and southern Russia. It inhabited sparse forests and riverine corridors in this region until the 1970s. This population was regarded as a distinct subspecies and assessed as extinct in 2003. Results of a phylogeographic analysis evinces that the Caspian and Siberian tiger populations shared a common continuous geographic distribution until the early 19th century. Some Caspian tigers were intermediate in size between Siberian and Bengal tigers. It was also called Balkhash tiger, Hyrcanian tiger, Turanian tiger, and Mazandaran tiger (). Taxonomy Felis virgata was a scientific name used by Johann Karl Wilhelm Illiger in 1815 for the greyish tiger in the area surrounding the Caspian Sea. Tigris septentrionalis was the scientific name proposed by Konstantin Satunin in 1904 for a skull and mounted skins of tigers that were killed in the Lankaran Lowland in the 1860s. Felis tigris lecoqi and Felis tigris trabata were proposed by Ernst Schwarz in 1916 for tiger skins and skulls from Lop Nur and Ili River areas, respectively. In 1929, Reginald Innes Pocock subordinated the tiger to the genus Panthera. For several decades, the Caspian tiger was considered a distinct tiger subspecies. In 1999, the validity of several tiger subspecies was questioned. Most putative subspecies described in the 19th and 20th centuries were distinguished on basis of fur length and colouration, striping patterns and body size, hence characteristics that vary widely within populations. Morphologically, tigers from different regions vary little, and gene flow between populations in those regions is considered to have been possible during the Pleistocene. Therefore, it was proposed to recognize only two tiger subspecies as valid, namely P. t. tigris in mainland Asia, and P. t. sondaica in the Greater Sunda Islands and possibly in Sundaland. At the start of the 21st century, genetic studies were carried out using 20 tiger bone and tissue samples from museum collections and sequencing at least one segment of five mitochondrial genes. Results revealed a low amount of variability in the mitochondrial DNA in Caspian tigers; and that Caspian and Siberian tigers were remarkably similar, indicating that the Siberian tiger is the genetically closest living relative of the Caspian tiger. Phylogeographic analysis