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The Tertiary sediments of northern Pakistan are an exceptional record of terrestrial sedimentation and represent most of Neogene time. Foremost is the Siwalik Group of the Potwar Plateau, for which multiple, superposed fossil levels span ∼18–6 Ma. Well-developed magnetostratigraphic control provides secure dating so that Siwalik fossil horizons may be interpolated into a time scale with resolution to 100,000 years. We describe the geographic setting of the Potwar, give an overview of the temporal distribution of faunas, and discuss changes in paleohabitat and paleoecology with coinciding faunal change, as seen from the Siwalik viewpoint. The long Siwalik biostratigraphy of many successive assemblages with its resolved time scale may be compared directly with other well-dated sequences. Immigrant arrival and timing of faunal change may be traced. The basins of the Iberian Peninsula show somewhat different timing of introduction of hipparionine horses, and faunal turnover in the Siwaliks clearly precedes the Vallesian crisis in Spain. In contrast to the increasingly seasonal precipitation of the late Miocene Potwar, the paleohabitat of coeval North China appears to have been moist and equable, with high diversity faunas. Continued development and comparison of resolved Neogene records allow increasing resolution of the patterns of faunal change on regional to global levels.

The Siwalik formations of northern Pakistan consist of deposits of ancient rivers that existed throughout the early Miocene through the late Pliocene. The formations are highly fossil- iferous with a diverse array of terrestrial and freshwater vertebrates, which in combination with exceptional lateral exposure and good chronostratigraphic control allows a more detailed and tem- porally resolved study of the sediments and faunas than is typical in terrestrial deposits. Conse- quently the Siwaliks provide an opportunity to document temporal differences in species richness, turnover, and ecological structure in a terrestrial setting, and to investigate how such differences are related to changes in the fluvial system, vegetation, and climate. Here we focus on the interval between 10.7 and 5.7 Ma, a time of significant local tectonic and global climatic change. It is also the interval with the best temporal calibration of Siwalik faunas and most comprehensive data on species occurrences. A methodological focus of this paper is on controlling sampling biases that confound biological and ecological signals. Such biases include uneven sampling through time, differential preservation of larger animals and more durable skeletal elements, errors in age-dating imposed by uncertainties in correlation and paleomagnetic timescale calibrations, and uneven tax- onomic treatment across groups. We attempt to control for them primarily by using a relative-abun- dance model to estimate limits for the first and last appearances from the occurrence data. This model also incorporates uncertainties in age estimates. Because of sampling limitations inherent in the terrestrial fossil record, our 100-Kyr temporal resolution may approach the finest possible level of resolution for studies of vertebrate faunal changes over periods of millions of years. Approximately 40,000 specimens from surface and screenwash collections made at 555 localities form the basis of our study. Sixty percent of the localities have maximum and minimum age esti- mates differing by 100 Kyr or less, 82% by 200 Kyr or less. The fossils represent 115 mammalian species or lineages of ten orders: Insectivora, Scandentia, Primates, Tubulidentata, Proboscidea, Pholidota, Lagomorpha, Perissodactyla, Artiodactyla, and Rodentia. Important taxa omitted from this study include Carnivora, Elephantoidea, and Rhinocerotidae. Because different collecting methods were used for large and small species, they are treated separately in analyses. Small spe- cies include insectivores, tree shrews, rodents, lagomorphs, and small primates. They generally weigh less than 5 kg. The sediments of the study interval were deposited by coexisting fluvial systems, with the larger emergent Nagri system being displaced between 10.1 and 9.0 Ma by an interfan Dhok Pathan sys- tem. In comparison to Nagri floodplains, Dhok Pathan floodplains were less well drained, with smaller rivers having more seasonally variable flow and more frequent avulsions. Paleosol se- quences indicate reorganization of topography and drainage accompanying a transition to a more seasonal climate. A few paleosols may have formed under waterlogged, grassy woodlands, but most formed under drier conditions and more closed vegetation. The oxygen isotopic record also indicates significant change in the patterns of precipitation be- ginning at 9.2 Ma, in what may have been a shift to a drier and more seasonal climate. The carbon isotope record demonstrates that after 8.1 Ma significant amounts of C 4 grasses began to appear and that by 6.8 Ma floodplain habitats included extensive C4 grasslands. Plant communities with predominantly C3 plants were greatly diminished after 7.0 Ma, and those with predominantly C4 plants, which would have been open woodlands or grassy woodlands, appeared as early as 7.4 Ma. Inferred first and last appearances show a constant, low level of faunal turnover throughout the interval 10.7-5.7-Ma, with three short periods of elevated turnover at 10.3, 7.8, and 7.3-7.0 Ma. The three pulses account for nearly 44% of all turnover. Throughout the late Miocene, species richness declined steadily, and diversity and richness indices together with data on body size imply that community ecological structure changed abruptly just after 10 Ma, and then again at 7.8 Ma. Be- tween 10 and 7.8 Ma the large-mammal assemblages were strongly dominated by equids, with more balanced faunas before and after. The pattern of appearance and disappearance is selective with respect to inferred habits of the animals. Species appearing after 9.0 Ma are grazers or typical of more open habitats, whereas many species that disappear can be linked to more closed vege- tation. We presume exceptions to this pattern were animals of the mixed C

The Lower Siwalik, Chinji Formation (Late Miocene) of the Chinji Village area, northern Pakistan has provided remarkable material for the study of terrestrial fossil faunas, magnetic reversal stratigraphy and fluvial sedimentology. This paper considers patterns in the sedimentary stratigraphy, using magnetic reversals to constrain the time framework, and focusing on an intermediate (kilometre) horizontal length-scale. The project aimed to determine the architecture and time relationships of the channel sandstone bodies in a panel 300 m in stratigraphic thickness, and 11 km in horizontal length (along stratigraphic strike). This panel (the 1990 Fence) trends at a high angle to the flow direction of the Late Miocene river channels, and represents about 2 Ma of sediment accumulation. There is a continuous range in thickness of the sandstone bodies, but they can be usefully classified into (i) microbodies, (ii) minor sheets, (iii) thin mega-sheets and (iv) thick mega-sheets. The microbodies are probably mainly marginal features of the thicker bodies. The minor sheets were formed by small river channels, and the mega-sheets were formed as the deposits of the largest, generally braided, channel belts. Two aspects of the intermediate length-scale architecture of the Chinji Formation are analysed: (1) the presence in the Fence of three thick mega-sheets separated by two mudstone-dominated intervals that lasted for about 0.5 and 1.0 Ma, respectively and (2) the abrupt upwards increase in sandstone/mudstone proportions that defines the upper stratigraphic boundary of the Chinji Formation. We suggest that each of the three thick mega-sheet episodes resulted from avulsions into the area of large-channel belt complexes that formed central features of the Chinji river network and were each constrained by scarps or valley-side slopes during episodes of net deposition that lasted for about 100 ka, and may have resulted from climate and/or sea-level changes. The regional upward change from mudstone- to sandstone-domination at the top of the Chinji Formation resulted from a similar, but one-off, and more widespread, change in plan-view style of the river network, produced either by tectonic change in the mountain source area, or by climatic change.

Small mammals from two mid-Pliocene localities in Azad Kashmir produce a modern shrew comparableto living Suncus and murids assignable to three genera. These are Golunda kelleri , a species described previously from an early Pleistocene locality in northern Pakistan, cf. Hadromys sp., and Mus sp. The murids date to about 3 Ma and thus include the oldest record of Golunda and of the Hadromys lineage.

Two new small-sized bovid species are described from the Miocene of Pakistan (Kamlial and Vihowa formations, about 18 Ma), based on associated dentitions and horn cores. Eotragus noyei, sp. nov. is probably ancestral to all younger Eotragus and the modern Boselaphini. E. noyei has a horn core which does not have a pronounced anterior concavity and posterior convexity seen in younger Eotragus species and it has primitive teeth with inclined buccal walls. The indeterminate genus and species from the Vihowa Formation has compressed, keeled horn cores and more advanced teeth with vertical buccal walls. The morphology of the horn cores suggests that this taxon could represent the earliest known member of the keeled Boselaphini. If this hypothesis is correct, we are witnessing the presence in Pakistan of the first split within the Boselaphini (keeled Miocene species versus Eotragus and modern taxa).

We compare the taphonomy of vertebrate assemblages from two long continental records—the early Paleogene of the Bighorn Basin, Wyoming, and the Neogene Siwalik sequence of northern Pakistan. Both sequences contain a similar array of fluvial facies, and the abundance of these facies differs among formations. We document environments of preservation of vertebrate localities over time to determine comparability of fossil assemblages within and between sequences. Changes in sample size and species richness are noted to reveal potential sampling effects on patterns of faunal turnover. Preservational history determined the environment, sample size, quality of specimens, taxonomic composition, and spatial and temporal resolution of fossil assemblages and thereby the quality of the fossil record and its suitability for further analyses. In both sequences, changes in prevailing taphonomic processes reflect changes in lithofacies and habitat distribution. Correlated changes are found in fossil productivity, species richness, and faunal composition. Both sequences contain some episodes of apparent faunal change in which appearances and disappearances of rare taxa can be attributed principally to changes in sample size. The Paleogene record has high taxonomic resolution (i.e., to genus or species) for most mammalian fossil remains. Temporal and spatial averaging of Paleogene fossil assemblages changes with lithofacies. The Neogene record has higher taxonomic resolution for remains of small mammals ( Different preservational circumstances impose different constraints on paleocological and evolutionary analyses. The best opportunities for paleocommunity reconstruction are provided by high taxonomic resolution, large samples, nd varied environments of preservation. These circumstances are found in limited portions of each record. The best opportunities for documenting evolution within lineages and species-replacement patterns are provided by high taxonomic resolution, high temporal resolution, and consistent preservational context. These taphonomic attributes pertain to the more common Paleogene mammals, particularly from the rich paleosol localities of the Willwood Formation, and to the more common Neogene small mammals from abandoned-channel fills of the Siwalik record.

The fluvial Neogene Siwalik formations of northern Pakistan contain a long and richly fossiliferous sequence of terrestrial vertebrate faunas in which patterns of faunal turnover and changes in diversity can be documented and analyzed for intervals having durations of 0.5 m.y. The complete sequence extends from circa 18.5 to 1 Ma, but the part between 18.5 and 5.5 Ma is best sampled, and most intervals within it are well represented. Thirteen orders of Siwalik mammals have been identified, with well-sampled intervals having 50 or more species. Most Siwalik mammals, however, are either rodents or artiodactyls. Bovids are the most common and most speciose of the larger mammals, while murid and “cricetid” rodents dominate the small mammal assemblages. Between 18.5 and 5.5 Ma species diversity varied considerably. Among artiodactyls and rodents the number of species first increased between 15 and 13 Ma and then fell. Data on stratigraphic ranges of rodents and artiodactyls show that faunal change in the Siwaliks was episodic, occurring during short intervals with high turnover followed by longer periods with considerably less change. Maxima of first appearances occurred at approximately 13.5 and 8.5 Ma, while maxima of last occurrences were at 12.5 and 8.0 Ma. Some of the observed faunal events can be correlated to climatic and environmental changes. The Middle Miocene diversification occurred during a period of global cooling, while the latest Miocene decline in diversity and increased turnover accompanied oxygen and carbon isotopic changes that correlate to globally increasing seasonality and aridity. Other correlations are ambiguous. The marked decrease in diversity and the major turnover events between 13 and 8 Ma do not correspond to known local or global events. The Neogene Siwaliks and Paleogene Bighorn-Crazy Mountains sequence in Wyoming and Montana share many similarities. They have equivalent levels of temporal resolution and similar levels of completeness of their fossil records. Siwalik ordinal abundance and diversity patterns differ markedly from those of the Paleogene, but generic, and probably species, diversity was approximately the same, although the Siwalik faunas may have been slightly less diverse. Over time, changes in diversity were of comparable magnitude, with monotonic trends persisting for more than 5 million years. The magnitude of faunal turnover was also similar, ranging from less than half to 3.5 times that expected. In both sequences faunal change appears to have been episodic, with strong pulses between intervals of low turnover. The Siwaliks, in contrast to the Paleogene sequence, may have had more distinct pulses and longer intervals between pulses. Neither sequence has peaks of first occurrences coinciding with peaks of last occurrences.

MODERN whales (order Cetacea) are marine mammals that evolved from a land-mammal ancestor, probably a cursorial Palaeocene–Eocene mesonychid1–3. Living whales are streamlined, lack external hind limbs, and all swim by dorsoventral oscillation of a heavily muscled tail4,5. A steamlined rigid body minimizes resistance, while thrust is provided by a lunate horizontal fluke attached to the tail at a narrow base or pedicle6. We describe here a new 46–47-million-year-old archaeocete intermediate between land mammals and later whales. It has short cervical vertebrae, a reduced femur, and the flexible sacrum, robust tail and high neural spines on lumbars and caudals required for dorsoventral oscillation of a heavily muscled tail. This is the oldest fossil whale described from deep-neritic shelf deposits, and it shows that tail swimming evolved early in the history of cetaceans.

The magnetostratigraphy of the Chinji Formation (Siwalik Group, Pakistan) provides age estimates for the earliest occurrence of hominoids attributable toSivapithecus. This report documents a new earliest occurrence for the genus and provides age estimates for other Chinji Formation specimens described previously. These middle Miocene primates have figured prominently in discussions of the course and timing of hominoid evolution.Sivapithecus shares with the living orang-utan (Pongo) a number of derived craniofacial features indicating that they are sister taxa. The newly discovered specimens from the Chinji Formation therefore provide a minimum estimate for the time of the initial divergence between the Asian and African large hominoid clades. Large-bodied hominoids first appear in the Siwaliks at 12·5 m.y.a., with specimens preserving the derived craniofacial features dated at ∼ 12 m.y.a. This age estimate can be used to calibrate branching times of extant hominoids as determined from comparative molecular data.

The Paleogene of Wyoming and Montana and the Neogene Siwaliks of Pakistan contain deposits representing a wide variety of terrestrial environments. Although fossils are preserved in all of these environments, fossil vertebrates are abundant in only certain facies. These principal preservational environments vary within and, particularly, between formations in each region.The Bighorn and Crazy Mountain basins of Wyoming and Montana contain abundant remains of Paleocene and Eocene vertebrates. Over 1800 localities in this region have been established in the Paleocene Fort Union and Paleocene to Eocene Willwood formations. The distribution of vertebrate remains changes dramatically upsection in this sequence. The Fort Union consists of thick fluvial sandstones and minor swampy floodplain mudstones in the lower part, and more widely separated channel sandstones interbedded with better drained floodplain deposits that include paleosol horizons in the upper part. These changes reflect a local increase in aggradation rate. Vertebrates are preserved almost exclusively in channel mud-clast conglomerates in the lower part of the formation, but appear in a wider variety of environments (channels, splays, swamps, and paleosols) in the upper part. The Willwood Formation continues the changes evident in the upper Fort Union. With increased aggradation rates, floodplain deposits became thicker and more well drained. Except for rare occurrences in other environments (channels, a variety of calcareous environments, and oxbows), fossils are recovered primarily from paleosol horizons developed in fine grained floodplain deposits.The Fort Union channel deposits contain assemblages that are often highly biased samples of faunal composition with large aquatic taxa well represented and small terrestrial forms unevenly represented. The upper Fort Union and Willwood floodplain paleosols contain more homogeneous (and therefore comparable) assemblages. These paleosols differ systematically, however, in terms of soil maturity and vertebrate composition, and they are commonly biased against large or aquatic taxa.The distribution of Siwalik vertebrate localities among sedimentary environments is known for four formations spanning early middle to late Miocene: Kamlial, Chinji, Nagri, and Dhok Pathan. The principal deposits in which fossils occur are: major stream channel complexes, secondary (floodplain) channels, crevasse splays, and floodplains. The Kamlial and Nagri formations, dominated by coarse lithologies (>50% sandstone), are notably less productive of fossil localities than the Chinji and Dhok Pathan formations, dominated by fine grained lithologies (>50% mudstone). In the Kamlial and Nagri formations, major channel complexes form the most prevalent environment, and more localities are associated with these channels than with any other environment. In the Chinji and Dhok Pathan formations, the most prevalent environment is floodplain, but more localities are associated with the secondary channels on these floodplains than with any other environment. In the Chinji Formation, most localities developed in secondary channels occur in fining-upward fill sequences, whereas in the Dhok Pathan Formation, most sites in these channels occur in their lag deposits. In these more productive formations, the abundance of certain mammalian taxa is correlated with specific depositional environments. Change upsection in the abundance of these taxa could result largely from change in facies productivity.The taphonomy of the two areas is similar in that channel lag deposits are an important source of fossil vertebrates. The major difference is that the Rocky Mountain Paleogene contains fewer, but highly productive, environments that changed significantly through time, including the Eocene emergence of floodplain paleosols as the primary environment of vertebrate preservation.

The Manchar Formation, a middle and upper Miocene fluvial sequence of sandstones, silts, and conglomerates, is exposed in a narrow north–south belt in the Lower Indus Basin of Sind Province, Pakistan. The formation, as measured in geological sections near Lake Manchar, can be divided into three parts differing in the proportions of the sandstones and silts. The contact with the underlying marine Gaj Formation is gradational; when the base of the Manchar Formation is taken as the lowest thick sandstone of fluvial origin, it lies above the highest marine or estuarine beds. Fossil localities cluster into three stratigraphie groups which correspond to the three horizons previously recognized. New additions to the Manchar faunas include a large hominoid and another small primate, two creodonts, three amphicyonids, a shovel-tusked amebelodontine, a chalicothere, species of Orycteropus, Zygolophodon, Stegolophodon, and Brachyodus, a species comparable to Tetraconodon minor, two small species of Dorcathe...

We report here eight new hominoid specimens, attributable to Ramapithecus and Sivapithecus1,2, from the middle Miocene Chinji Formation of Pakistan. Hominoids previously described from the Chinji Formation cannot be precisely located although they most probably come from the upper two-thirds of the formation3–9. The new material, from the middle portion of the formation, is ∼12–13 Myr old based on magnetostratigraphy (refs 10, 11 and N. Johnson, personal communication). Two earlier specimens are supposedly from the underlying Kamlial Formation6,12, although the best candidate for an earliest Ramapithecus or Sivapithecus is an undescribed molar, AMNH 19565B, collected by Brown13 from a locality believed to be basal Chinji14, for which magnetostratigraphy indicates an age of 14.5 Myr (ref. 11 and N. Johnson, personal communication). Small hominoids are definitely known in the older Manchar Formation in Sind15. Together with the material discussed here, the new specimens record the earliest phases of Asian hominoid evolution following dispersal from Africa–Arabia16, and the apparent division of large hominoids into ‘African’ (lineages leading to Pan, Gorilla and Homo) and ‘Asian’ (leading to Pongo) clades at a minimum of 13 Myr17–19, probably more.

The fluvial Neogene Siwalik formations of northern Pakistan span long time intervals with only minor hiatuses and, being highly fossiliferous, are uniquely suited for studies of change in mammalian faunas. Magnetostratigraphic correlations of a critical stratigraphic section give dates for 45 middle and late Miocene biostratigraphic events. These mark either first appearances or extinctions in the mammal fauna and show that in the Siwaliks there were major fauna turnovers at between 20 and 16 Ma and at 9.5 and 7.4 Ma. Two minor faunal events are dated at 13.2 and about 12 Ma. Many species making their first appearance were immigrants from Europe or Africa and indicate when connections to those regions existed. Immigration and extinction were the dominant modes of faunal change; in situ evolution was much less important. The Siwalik biostratigraphic record correlates closely to climatic, oceanographic, and tectonic events, which probably controlled immigration into southern Asia. Abiotic events were therefore important factors affecting evolution of the mammal communities.