Craniometric variation in the tiger (Panthera tigris): Implications for patterns of diversity, taxonomy and conservation

Patterns of geographical variation in tigers are reviewed extensively by a morphometric analysis based on 273 skulls of certain wild origin. The following principal observations emerging from this investigation are found:1.Modern tigers contain two basic forms: the mainland Asia tiger and the Sunda Island tiger. They are differentiated markedly in skull morphology as well as other morphological characters, the characteristic skull shape and small body size in Java/Bali tigers can be interpreted as adaptational responses to a particular island landscape type and prey species fauna, an evolutionary process known as insular dwarfism.2.The Sumatran tiger (P.t. sumatrae) probably represents a hybrid of mainland and Island tigers, which originated from mainland Southeast Asia, colonized Indonesia and hybridized with the Sunda island tigers (Java tiger) during the late Pleistocene, and was subsequently completely isolated from both the mainland Southeast Asia and Java/Bali populations.3.Among the mainland Asia tigers, the Amur or Siberian tiger is the most distinct; India, Indochinese and South China tigers are craniometrically distinguishable on average, but with clear overlaps; the Caspian tiger, on the other hand, is indistinguishable from other mainland forms and extensively overlaps with both the Northern and Southern Asia subspecies.4.Most proportional craniometric differences among tigers observed from this study are mainly allometric; the pattern of craniometric variation in mainland tigers is clearly clinal; craniometric variation and sexual dimorphism are closely related.5.Skull morphometric characters are quite effective for discriminating major tiger geographical populations, but further analysis using other phenetic craniodental characters (shape of sagittal crest, degree of convexity of the frontal, endocranial volume, detailed carnassial morphology) as well as molecular genetic sources, rather than this purely metric study, would certainly be of considerable value in understanding the evolutionary relationships among mainland Asia tigers and their appropriate taxonomic designations.