in continental Asia as P. t. tigris, and those in the Sunda Islands as P. t. sondaica. This two-subspecies view is still disputed by researchers, since the currently recognized nine subspecies can be distinguished genetically. Results of a 2018 whole-genome sequencing of 32 specimens support six monophyletic tiger clades corresponding with the living subspecies and indicate that the most recent common ancestor lived about 110,000 years ago. The following tables are based on the classification of the species Panthera tigris provided in Mammal Species of the World, and also reflect the classification used by the Cat Classification Task Force in 2017: Evolution The tiger's closest living relatives were previously thought to be the Panthera species lion, leopard and jaguar. Results of genetic analysis indicate that about 2.88 million years ago, the tiger and the snow leopard lineages diverged from the other Panthera species, and that both may be more closely related to each other than to the lion, leopard and jaguar. The geographic origin of the Panthera is most likely northern Central Asia. The tiger–snow leopard lineage dispersed in Southeast Asia during the Miocene. Panthera zdanskyi is considered to be a sister taxon of the modern tiger. It lived at the beginning of the Pleistocene about two million years ago, its fossil remains were excavated in Gansu of northwestern China. It was smaller and more "primitive", but functionally and ecologically similar to the modern tiger. It is disputed as to whether it had the striping pattern. Northwestern China is thought to be the origin of the tiger lineage. Tigers grew in size, possibly in response to adaptive radiations of prey species like deer and bovids, which may have occurred in Southeast Asia during the Early Pleistocene. Panthera tigris trinilensis lived about and is known from fossils excavated near Trinil in Java. The Wanhsien, Ngandong, Trinil, and Japanese tigers became extinct in prehistoric times. Tigers reached India and northern Asia in the late Pleistocene, reaching eastern Beringia, Japan, and Sakhalin. Some fossil skulls are morphologically distinct from lion skulls, which could indicate tiger presence in Alaska during the last glacial period, about 100,000 years ago. Fossil teeth and bones found in Borneo were attributed to the Bornean tiger and date to about 13,745 to 3,000 years ago. It may have accessed Borneo, when the sea level was low during a glaciation period, and may have survived until about 200 years ago.