Small mammal indicators of forest paleoenvironment in the Siwalik deposits of the Potwar Plateau, Pakistan

The Siwalik Group comprises a thick sequence of terrestrial deposits in the northern part of the Indian Subcontinent, with a relatively high degree of completeness over most of Neogene time. Derived from highlands to the north, the Siwaliks were deposited by river systems that preserved many superposed fossil assemblages that are well dated. In the Potwar Plateau of northern Pakistan, the fossil record is good for the interval of 18 to 6 Ma; deposits elsewhere and in India complement it. The record as a whole shows historical trends that test interpretations of paleoenvironments. Principle conclusions are these: (1) high mid-Miocene faunal diversity persisted until 10 Ma; (2) decreasing diversity is a sustained trend through the late Miocene; (3) mid-Miocene small mammal elements indicate considerable arboreal habitat; (4) forest elements decline slightly in diversity through 11 Ma, with return to higher proportions by 8 Ma; (5) open/grass adapted elements begin to appear in the interval of 9 - 8 Ma, and arboreal elements show turnover, with decline to a lower proportion by 7 Ma. The trends indicate sustained change that is not abrupt, and there is no major restructuring of the fauna until about 8 Ma. Late Miocene faunal change indicates changing arboreal habitat, which likely corresponds to increasing seasonality and fragmentation of formerly widespread forest. In general, modern mammalian analogues appear to be useful for interpreting habitat preferences of Miocene fossil rodents, but an apparent exception is the gundi Sayimys, which may have been a subtropical element unlike arid-adapted modern relatives.