Origin of a Subtropical Fauna in the Middle Latitude as Exemplified by the Kakegawa Fauna

The pliocene Kakegawa fauna represents the last invasion of the subtropical fauna into southwest Japan in the Neogene history. It shows a rather sharp biogeographic boundary northward and grades into the tropical fauna southward, suggesting that the origin of the Kakegawa fauna is intimately related to a tropical fauna. While only a few characteristic Kakegawa elements are phyletically traced back to ancestral forms of the Middle Miocene Kadonosawa fauna of the antecedent tropical phase, major elements have the phyletic relation to the species of the southern Miocene. Origin of the Kakegawa fauna could be a result of speciation of the tropical species in the frontal fringe of distribution during northward expanding phase.