Over ten thousand fossil small mammal specimens represent the diverse Neogene-age microfaunas of northern Pakistan. The most productive area yielding by far the majority of the fossils is the Potwar Plateau, a >20,000 km2 region southwest of Islamabad, with a thick sequence of sedimentary deposits known as the Siwalik Group. The Siwaliks span early Miocene to early Pleistocene time (>18-<2 Ma), with rich, superposed fossil faunas throughout. In spite of an impressive set of fossil assemblages amassed over the course of 25 years, representation by fossil Lagomorpha (rabbits, hares, and pikas) remains poor. Throughout much of the sequence, lagomorphs appear to be absent, and where they occur, they are apparently rare.
Flynn et al. (1997) recovered a single isolated molar of an ochotonid (pika) from the base of the Siwalik Group. Similarly,
Wessels (2009) found limited evidence of an ochotonid in the Murree Formation at Sehwan, Sind Province.
Leporidae (rabbits and hares) have been known from the Indian Subcontinent for many years, but only from the Pliocene and younger deposits of northern India (Forsyth Major 1899;
2002). As the record of leporids emerged in Pakistan, it was noted at the family level in a series of reports, for example, by
Barry et al. (2002), who cited the family as ranging back to the late Miocene. We report here in greater detail the leporids from the Potwar Plateau, northern Pakistan, represented by approximately 20 cranial and postcranial specimens from nine localities, dating from the late Miocene to earliest Pleistocene.
The most continuous and well-exposed Siwalik series is found in northern Pakistan and best researched in the Potwar Plateau. The Siwaliks are fluvial deposits, thick clastic wedges derived from the uplift of the ranges adjacent to the Tibetan Plateau during the Neogene. On the Potwar Plateau, the Siwaliks are found in a folded belt extending from the Salt Range in the south to the Margala Hills in the north, and from the Jhelum River in the east to the Indus River in the west. Siwalik deposits are significant because they are highly fossiliferous and represent relatively continuous and complete sedimentation. The thick sequence is divided into formations recognized on the basis of dominant lithology. At the base is the Kamlial Formation that yielded the pika. The superposed Chinji Formation, including bright red mudstones and buff to bluish channel sands, has produced thousands of small mammals, but no lagomorphs. The subsequent Nagri Formation sandstones, dominantly bluish, also lack lagomorphs. It is the upper levels of the overlying Dhok Pathan Formation, mudstones related to mainly buff-colored channel sands, that produced the most and the oldest Leporidae. Thereafter, younger deposits (Soan Formation) have produced only one leporid tooth. These strata have been dated using paleomagnetic techniques (see below).
The Potwar Plateau lagomorphs are from localities Y457, Y921, Y456, Y581, Y908, Y975, DP13, DP8, and DP24. The geologically oldest Siwalik leporids (ca. 7.4 Ma; Y457 and Y921) show the group to have entered the Siwalik record late in the Miocene.
Barry et al. (2002) evaluated the density of fossil samples to estimate that the actual faunal introduction could have been as old as 7.8 Ma. All localities but DP8 and DP24 are near the village Hasnot. DP8 is younger, about 3.5 Ma, and from about 5 km north of Hasnot. The youngest locality that has produced lagomorphs in Pakistan is DP24 (ca. 1.7 Ma), which is in the Pabbi Hills to the east.
Barry et al. (2002) presented the Dhok Saira paleomagnetic log, the tool for dating deposits in the Hasnot area (Figure 1). This section near Hasnot correlates to chrons C4n.2n through C3An.2n of the geomagnetic polarity time scale. Interpolation assigns ages for localities resolvable at the scale of 105 years. Useful dates are thereby assigned to localities Y457, Y921, Y456, Y581, Y908, and DP13. Previous work assigned approximate ages for DP8 (late Gauss Chron,
Opdyke et al. 1979) and for DP24 (overlying the Olduvai event,
Keller et al. 1977). Y975 can be projected to about chron C3Bn in the Kotal Kund paleomagnetic section of
Opdyke et al. (1979).
Based on these interpretations, Leporidae are present in the Potwar Plateau at sites dating from the late Miocene to early Pleistocene. From oldest to youngest, most of the specimens are late Miocene in age (between 7.4 and 6.5 Ma). Three teeth from DP8 are Pliocene in age (ca. 3.5 Ma), and one specimen from DP24 is early Pleistocene (ca. 1.7 Ma).