indicates that the common ancestor of Caspian and Siberian tigers colonized Central Asia via the Gansu−Silk Road region from eastern China less than 10,000 years ago, and subsequently traversed eastward to establish the Siberian tiger population in the Russian Far East. The Caspian and Siberian tigers were likely a single contiguous population until the early 19th century, but became isolated from another due to fragmentation and loss of habitat during the Industrial Revolution. In 2015, morphological, ecological and molecular traits of all putative tiger subspecies were analysed in a combined approach. Results support distinction of the two evolutionary groups continental and Sunda tigers. The authors proposed recognition of only two subspecies, namely P. t. tigris comprising the Bengal, Malayan, Indochinese, South Chinese, Siberian and Caspian tiger populations, and P. t. sondaica comprising the Javan, Bali and Sumatran tiger populations. Tigers in mainland Asia fall into two clades, namely a northern clade formed by the Caspian and Siberian tiger populations, and a southern clade formed by populations in remaining mainland Asia. In 2017, the Cat Specialist Group revised felid taxonomy and now recognizes the tiger populations in continental Asia as P. t. tigris. However, a genetic study published in 2018 supported six monophyletic clades, with the Amur and Caspian tigers being distinct from other mainland Asian populations, thus supporting the traditional concept of six living subspecies. Characteristics Fur Photographs of skins of Caspian and Siberian tigers indicate that the main background colour of the Caspian tiger's fur varied and was generally brighter and more uniform than that of the Siberian tiger. The stripes were narrower, fuller and more closely set than those of tigers from Manchuria. The colour of its stripes was a mixture of brown or cinnamon shades. Pure black patterns were invariably found only on head, neck, the middle of the back and at the tip of the tail. Angular patterns at the base of the tail were less developed than those of Far Eastern populations. The contrast between the summer and winter coats was sharp, though not to the same extent as in Far Eastern populations. The winter coat was paler, with less distinct patterns. The summer coat had a similar density and hair length to that of the Bengal tiger, though its stripes were usually narrower, longer and closer set. It had the thickest fur amongst tigers, possibly due its occurrence in the temperate parts of Asia.