Vertebrate remains generally are rare in the fossil record as a whole, with each bone or tooth potentially representing a new and important piece of the evolutionary puzzle.  Long hours of field surveying combined with careful documentation and collection represent the mission of the professional paleontologist, even when the resulting specimens are fragmentary and hard to interpret.  In some eroding sedimentary rock sequences, however, vertebrate fossils are quite abundant, with fragmentary teeth and bones littering the surfaces of eroding hills and valleys.  Such places provide opportunities for a different kind of field surveying that involves careful documentation of large numbers of surface fossils along with limited collecting of only the most complete, informative specimens.  The Siwalik sequence of northern Pakistan has abundant vertebrate fossils that have eroded from thousands of meters of strata spanning millions of years during the Miocene Epoch (~18–5 million years ago).  Using a method called biostratigraphic surveying, which records all fossils found by survey teams within specific stratigraphic intervals and then compares data for successive intervals, we examine trends through time in the numbers of identifiable fossils, the types of skeletal parts, and kinds of animals that inhabited the ancient ecosystems of the ancestral Indus and Ganges alluvial plains on the Indian sub-continent.