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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.

Isotopic analyses of mammalian tooth enamel from a well-defined, laterally extensive 150 k.y. interval (9.15–9.30 Ma) reveal an ecological gradient in vegetation on the late Miocene sub-Himalayan alluvial plain. Two contemporaneous river systems deposited the sediments of this interval, with a mountain-sourced system (herein, Blue-gray) to the southwest interfingering with a foothill-sourced system (Buff) to the northeast. Fossil mammal teeth collected from a 32 km transect across this fluvial gradient are significantly more depleted in 13C from northeastern localities than from southwestern localities. This trend occurs in equids, giraffids, suids, sivapithecine hominoids, and anthracotheres. We propose that the Buff fluvial system provided more equably moist substrate conditions and supported more closed-canopy vegetation than the Blue-gray fluvial system. Herbivores living along the paleovegetation gradient thus acquired different carbon isotopic signatures during the period of tooth enamel formation, resulting from higher δ13C values in the forage supported by the Blue-gray fluvial system compared with forage associated with the Buff system. The data also imply that many Siwalik mammalian herbivores displayed marked fidelity in juvenile home ranges and habitats.

The discovery of the skull known as Toumai four years ago in Chad began a controversy. Faunal studies suggested an age close to 7 million years; a small cranium suggested chimpanzee-like brain size. The team that found Toumai considered it to be a hominid on our side of the chimp-human divide, but others thought it more ape-like. Important finds of teeth and jaw pieces of the Toumai species, Sahelanthropus tchadensis, now help to distance the species from apes, suggesting that it is a hominid closely related to the last common ancestor of chimps and humans. A virtual reconstruction of the Toumai cranium provides more evidence of a close relationship to humans — and this week's cover. You are looking at the face of the earliest known hominid. (Cover by MPFT; M. Brunet, E. Daynes, Ph. Plailly and A. Garaudel contributed). Discoveries in Chad by the Mission Paleoanthropologique Franco-Tchadienne have substantially changed our understanding of early human evolution in Africa1,2,3. In particular, the TM 266 locality in the Toros-Menalla fossiliferous area yielded a nearly complete cranium (TM 266-01-60-1), a mandible, and several isolated teeth assigned to Sahelanthropus tchadensis3 and biochronologically dated to the late Miocene epoch (about 7 million years ago). Despite the relative completeness of the TM 266 cranium, there has been some controversy about its morphology and its status in the hominid clade4,5. Here we describe new dental and mandibular specimens from three Toros-Menalla (Chad) fossiliferous localities (TM 247, TM 266 and TM 292) of the same age6. This new material, including a lower canine consistent with a non-honing C/P3 complex, post-canine teeth with primitive root morphology and intermediate radial enamel thickness, is attributed to S. tchadensis. It expands the hypodigm of the species and provides additional anatomical characters that confirm the morphological differences between S. tchadensis and African apes. S. tchadensis presents several key derived features consistent with its position in the hominid clade close to the last common ancestor of chimpanzees and humans.

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

Fossils from a large-bodied hominoid from early Miocene sediments of Uganda, along with material recovered in the 1960s, show features of the shoulder and vertebral column that are significantly similar to those of living apes and humans. The large-bodied hominoid from Uganda dates to at least 20.6 million years ago and thus represents the oldest known hominoid sharing these derived characters with living apes and humans.

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.

The Siwalik sequence, particularly the interval from 18 to 7 Ma, provides one of the few terrestrial data sets that allows direct measurement of temporal durations of mammalian species. Its data are drawn from a single biogeographic subprovince and superposed collections likely represent successive samples of single lineages. Observed temporal ranges underestimate total species longevities if (1) species existed in other biogeographic provinces before or after the temporal ranges recorded in the Siwaliks, or (2) the fossil record inadequately samples species durations in the Siwalik subprovince. Some data, notably from Afghanistan, China, and Thailand, bear on the first variable. The second can be controlled by considering data quality, in this case the temporal distribution of good data sets, to assess the scale of accuracy available for defining range endpoints. In general, range endpoints can be estimated to the nearest 0.1 million years.The diverse Rodentia give a mean species longevity of 2.2 million years for the Miocene Siwaliks. This includes single records, but of course ignores unretrieved rare or short-lived taxa. The diverse Artiodactyla yield 3.1 million years. The difference may reflect greater body size and longer generation time; large Perissodactyla and Proboscidea have longer temporal ranges. Carnivorous mammals also show about 3 million year durations. Given these data, the average longevity for Sivapithecus species (1.6 million years) is modest. The deposits of the Clarks Fork Basin, Wyoming, offer a Paleogene data set comparable to that of the Neogene Siwaliks. Paleocene-Eocene mammals of North America yield shorter longevities (most less than one million years).Extinction is the dominant mode of species termination for Siwalik mammals. Most taxa originated by immigration (as at about 13.5 Ma) or abrupt speciation. There are some cases for insitu transformation of lineages, for example in the genera Punjabemys, Antemus, Percrocuta, Dorcatherium, Giraffokeryx, and Selenoportax. The rodent Kanisamys shows a rate of increase in tooth size of 0.5 darwins. This overall rate is moderate by Paleogene standards, but includes an interval of more rapid change between 9.0 and 8.5 Ma.

The Siwalik Sequence of northern Pakistan contains a 16-Ma record of paleosol carbonate and fossil teeth from which a record of paleovegetation can potentially be reconstructed and compared. The carbon isotopic composition of paleosol carbonate and organic matter from Siwalik strata reflects a major paleoecological change on the floodplains of major rivers beginning7.3 Ma ago. By 6 Ma C 3 -dominated plant communities, probably composed of mostly trees and shrubs, were displaced by nearly continuous C 4 grassland. We find that the carbon isotopic ratios in herbivore tooth enamel reflect this dramatic ecologic shift. Carbonate in enamel older than 7 Ma averages −11‰ in δ 13 C PDB , consistent with a largely C 3 diet. Enamel from the Plio-PIeistocene averages +1.9‰ in δ 13 C, similar to the value displayed by modern C 4 grazers. Analysis of post-burial carbonate cements, and the concordance with isotopic evidence from paleosols argues strongly against major isotopic alteration of the enamel, while coexisting bone may have been altered early in burial. This study confirms that enamel apatite is useful for paleodietary reconstruction much further back in the geologic record than was previously thought.

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.

Problems of stratigraphic completeness and poor temporal resolution make analysis of faunal change in terrestrial sequences difficult. The fluvial Neogene Siwalik formations of India and Pakistan are an exception. They contain a long vertebrate record and have good chronostratigraphic control, making it possible to assess the influence of biotic interchange on Siwalik fossil communities. In Pakistan, the interval between 18 and 7 Ma has been most intensively studied and changes in diversity and relative abundance of ruminant artiodactyls and muroid rodents are documented with temporal resolution of 200,000 years. Within this interval, diversity varies considerably, including an abrupt rise in species number between 15 and 13 Ma, followed by a decline in ruminant diversity after 12 Ma and a decline in muroid diversity in two steps at 13 and 10 Ma. Significant changes in relative abundance of taxa include an increase in bovids between 16.5 and 15 Ma, a decrease in tragulids after 9 Ma, and a very abrupt increase in murids at 12 Ma. Megacricetodontine rodents also decrease significantly at 12 Ma, and smaller declines are recorded among myocricetodontine and copemyine rodents after 16 Ma. An increase of dendromurine rodents at 15.5 Ma is also observed. There is also a trend of progressive size increase among giraffoids and bovids throughout the sequence.We have also investigated relationships between biotic interchange and diversity, body size, and relative abundance, concluding that (1) the rapid increase in ruminant and muroid diversity was largely due to immigration, whereas in situ speciation had only a secondary role; (2) during intervals of increasing diversity, resident lineages did not have higher than average rates of in situ speciation; (3) during intervals with rising diversity, greater extinction did not accompany increased immigration; (4) during intervals with falling diversity, there may have been greater extinction in recently invading lineages; and (5) change in diversity was independent of changes in relative abundance and body size.

Geohistorical records reveal the long-term impacts of climate change on ecosystem structure. A 5-myr record of mammalian faunas from floodplain ecosystems of South Asia shows substantial change in species richness and ecological structure in relation to vegetation change as documented by stable isotopes of C and O from paleosols. Between 8.5 and 6.0 Ma, C 4 savannah replaced C 3 forest and woodland. Isotopic historical trends for 27 mammalian herbivore species, in combination with ecomorphological data from teeth, show three patterns of response. Most forest frugivores and browsers maintained their dietary habits and disappeared. Other herbivores altered their dietary habits to include increasing amounts of C 4 plants and persisted for >1 myr during the vegetation transition. The few lineages that persisted through the vegetation transition show isotopic enrichment of δ 13 C values over time. These results are evidence for long-term climatic forcing of vegetation structure and mammalian ecological diversity at the subcontinental scale.

Magnetostratigraphy provides unparalleled chronologic precision for long terrestrial sedimentary records. The Siwaliks of the Potwar Plateau, northern Pakistan, present perhaps the best example of a sequence of well dated faunal horizons spanning most of the Neogene in a single terrestrial biogeographic province. Temporal control on fossil localities tied to multiple paleomagnetic sections is ca. 0.1 m.y., less given special conditions of short magnetozone duration or superpositional relationships. New correlations are presented for two long sections in the lower Siwaliks showing the power and the limitations of mag-netostratigraphic correlation within the Siwalik depositional setting. Correlation of Potwar fossil localities to those of an East African section, also dated paleomagnetically, are established with fossil localities from those two biogeographic provinces shown to be coeval on a scale of $$10^{5}$$ yr. The composite biostratigraphy rendered by the thick, well exposed, well dated Potwar Siwalik...

The recent reconstruction of the Sahelanthropus tchadensis cranium (TM 266-01-60-1) provides an opportunity to examine in detail differences in cranial shape between this earliest-known hominid, African apes, and other hominid taxa. Here we compare the reconstruction of TM 266-01-60-1 with crania of African apes, humans, and several Pliocene hominids. The results not only confirm that TM 266-01-60-1 is a hominid but also reveal a unique mosaic of characters. The TM 266-01-60-1 reconstruction shares many primitive features with chimpanzees but overall is most similar to Australopithecus , particularly in the basicranium. However, TM 266-01-60-1 is distinctive in having the combination of a short subnasal region associated with a vertical upper face that projects substantially in front of the neurocranium. Further research is needed to determine the evolutionary relationships between Sahelanthropus and the known Miocene and Pliocene hominids.

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The first sites with Pliocene and Pleistocene mammals west of the Rift Valley in Central Africa in northern Chad were reported in 1959 (ref. 1), and documented the presence of mixed savannah and woodland habitats. Further sites and a probable Homo erectus cranio-facial fragment were subsequently discovered. In 1993 a survey of Pliocene and Pleistocene formations in the Borkou-Ennedi-Tibesti Province of Chad (B.E.T.) led to the discovery of 17 new sites in the region of Bahr el Ghazal (classical Arabic for River of the Gazelles) near Koro Toro. One site, KT 12 (15 degrees 58'10"N, 18 degrees 52'46"E) yielded an australopithecine mandible associated with a fauna biochronologically estimated to be 3.0-3.5 Myr old. Australopithecine species described since 1925 are known from southern Africa and from sites spread along the eastern Rift Valley from Tanzania to Ethiopia (Fig. 1). This new find from Chad, which is most similar in morphology to Australopithecus afarensis, documents the presence of an early hominid a considerable distance, 2,500 km, west of the Rift Valley.

(2000). Chad: discovery of a vertebrate fauna close to the Mio-Pliocene boundary. Journal of Vertebrate Paleontology: Vol. 20, No. 1, pp. 205-209.

This brief commentary begins with my graduate work with Elwyn Simons which culminated in the 1965 “Preliminary Revision of the Dryopithecinae,” then about the most comprehensive review of the paleontological record of the great apes (Simons and Pilbeam, 1965). It reflected a time when that fossil record was dominated by teeth and fragmentary jaws, one decent skull, and a handful of postcranial remains. Much has changed since then, both in the record itself and in how it is interpreted, and what follows are reflections on where we are, how we got here, and where we might go next.

Nature 418, 145–151 (2002). Owing to an editorial oversight, the sentence in the second column of page 150 that reads ‘Lower c and the lower and upper premolars each have three pulp canals and two roots’ is in error. Instead, it should read ‘Lower and upper premolars each have three pulp canals and two roots’.

The results of excavations in Miocene deposits at Maboko Island, Western Kenya, in 1973 are described. An account is given of the geology, and it is concluded that the deposits form part of a sequence of floodplain overbank deposits. These consist mainly of diagenetically altered sediments laid down in wet conditions and they differ from the more dry conditions indicated by the pedogenetically altered sediments, with the development of calcretes, to the north of Majiwa and Kaloma. The Maboko fauna contains abundant aquatic elements whereas the Majiwa and Kaloma faunas have greater terrestrial affinities, although the differences between the faunas is small. Faunal analysis and radiometric data reported here suggest that the age of the Maboko fauna is about 15 Ma.

Siwalik deposits in the Punjab have yielded a rich collection of hominoidprimate remains. Together with other recent finds they indicate the need for some changes in hominoid classification.

The magnetic polarity zonation of the terrestrial strata exposed in the Dhok Pathan area of Pakistan has been established utilizing data from 204 paleomagnetic sites. Individual magnetic transitions are traced laterally over 15 km and provide convenient time lines for correlating the fluvial facies of the middle Siwalik Group. A pervasive, normal polarity zone dominates throughout the region and has been interpreted as Magnetic Polarity Epoch 9. Based on this interpretation and using the absolute ages from the published magnetic time scales the average sedimentation rate in the area is calculated at 0.8 m/1000 years, and the average elapsed time between fluvial cycles is 56,000 years. Major sandstone units are minimally time transgressive in an east-west direction. The Nagri Formation in the Dhok Pathan area spans the time from 10.0 to 8.6 m.y. B.P. Ramapithecus and other hominoid primates are found in Epoch 9 at about 9 m.y.

The phylogenetic affinites of Ramapithecus have been debated since its initial description in the 1930s. The concensus view that Ramapithecus represents the earliest hominid has been challenged by new evidence from molecular studies and the discovery of fossils which include formerly unknown parts of the facial skeleton. These suggest that the “ramamorphs” may be more closely related to Pongo than to the African apes and hominids. The implications of this interpretation of the Miocene hominoids requires re-evaluation of certain previous assumptions about pongid and hominid evolution.

The cranial capacity of Olduvai Hominid 7 is estimated to be 690 cc, with a standard uncertainty range of 538 to 868 cc. The estimate is derived from a systematic consideration of the relationships between Bregma-Asterion chords and cranial capacities obtained from a large sample of Homo sapiens and Pan troglodytes and from available fossil hominids. The estimation technique is applicable to other characters and specimens.

The period from 14 to four million years is poorly known in Africa, but during this time the Ethiopian fauna became established and hominids originated. The sedimentary sequence of the Tugen Hills in the Baringo area of Kenya provides important geological, environmental and plaeontological data concerning this interval. Concordant radiometric and palaeomagnetic determinations within the type section of the Ngorora Formation show that it spans more than 2 m.y., from 13 m.y.a. to less than 10 m.y.a., and from chrons 14 to 9. Other dates refine the calibration of the Younger Mpcsida, Lukeino and Chemeron units. Palaeontological results include the collection from the Ngorora Formation of one of the best Neogene macrofloras in Africa, and more fauna, including hominoids. No equids have been recorded older than 10 m.y.a. We also report new fauna from the more recent units.

One of the biggest problems facing palaeoanthropologists at the moment is the question of disagreement and definition.

(1972). Adaptive response of hominids to their environment as ascertained by fossil evidence. Social Biology: Vol. 19, No. 2, pp. 115-127.

A large ape existed in India at the close of the Miocene or the beginning of the Pliocene epochs; this ape shows a complex of anatomical structures at the opposite pole from its contemporary, Ramapithecus. Although found in the same beds, the two seldom occur at the same exact sites and levels. Considering the thickness of these beds, recovery close to Haritalyangar does not, of itself, prove sympatry of these two different kinds of Hominoidea. However, both are definitely present at one recently located site representing, most probably, a death assemblage. Observations by the authors on scores of chimpanzees suggest that, at least in this ape, wear gradients on molar crowns exist, but that the wear differential between adjacent molars is almost never raised to the degree seen in most Ramapithecus. Dryopithecus itdicus and D. fontani (from southern France), in contrast, show almost no wear gradient at all; that is, whether an individual is dentally young or old, wear on all three molars and the two premolars has proceeded to about the same degree. It is of considerable importance in understanding hominid phylogeny to be able to stress that an ape known to be contemporary with Ramapithecus shows far less differential wear than does the hominid. This, in turn, strongly suggests that the molar eruption sequence of D. indicus was rapid, while that of the hominid was delayed. The implication is that, as far back as the late Miocene, the hominid maturation period was lengthened, relative to that of apes. A further fact which emerges is that the rate of interstitial wear was faster in the Haritalyangar ape than in the hominid contemporary with it. This, together with its large size, flatness of unworn tooth crowns, and other associated characters, suggests that D. indicus is in, or close to, the ancestry of Gigantopithecus. From this emerges yet another object lesson, emphasizing the caution one has to observe in the manner and method by which ancient and modern apes are compared and contrasted. None of the species of Hominoidea dealt with here, whether pongid (D. indicus and Pan troglodytes) or hominid (R. punjabicus), accumulates either interstitial or crown wear at the same rate or in the same manner.

Neogene hominoid cranial material is regrettably scarce, especially from the middle and late Miocene. Between the 18-Myr-old virtually complete early Miocene Proconsul africanus skull from Rusinga1 and the 3–4-Myr-old Hadar hominoid cranial material2, the only significant large (non-hylobatid) hominoid facial or cranial specimens are those from the late Miocene Salonika in Greece3, Yassioren in Turkey4, Lufeng in China5, the possibly middle Miocene site of Moroto in Uganda6 and the new facial-mandibular piece from late Miocene deposits in Pakistan reported here. The specimen is a Sivapithecus indicus7 adult, probably male, and consists of most of the left side of the face including a small portion of the frontal bone, the zygomatic arch and temporo-mandibular joint, the maxilla, a virtually entire mandible and the complete dentition. The fossil, catalogued as GSP 15000, is the property of the Government of Pakistan and is at present on loan for study at Harvard University.

Fossil vertebrates discovered in 1986 from Cameroon, West Africa, occur in three different areas in the northern part of the country. Cretaceous rocks northeast of Garoua, in the Babouri-Figuil Basin, yield complete Lepidotes skeletons. Southeast of Garoua, Cretaceous rocks of the Mayo Rey Basin, near Koum, are more clearly terrestrial and contain diverse vertebrates. The Hama Koussou Basin, just north of Garoua, produces fragmentary Lepidotes and dinosaurs. Weathered from a veneer of Pleistocene sediment overlying the latter deposit, the well fossilized remains of Equus, Phacochoerus, and a bovid were recovered.

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.

Our knowledge of hominoid paleobiology has expanded dramatically in the past 10 years. Many new hominoid fossils have been recovered, principally from middle and late Miocene deposits in Europe and Asia. They are between 17 and 5 million years old. Comparative molecular studies on living hominoids have established a clear pattern of similarities and differences that almost certainly reflects a branching sequence. Broader “historical geological” research in many areas has enriched our knowledge of paleogeography, paleoclimates, and past faunas and floras considerably.

Analysis of enamel prism patterns in a selected series of extant hominoids reveals that pongids have a pattern distinctively different from that of Homo sapiens. The pattern for a Miocene hominoid, Ramapithecus, is very similar to that seen in Homo sapiens. The finding allows a new approach to the evaluation of isolated teeth.

The contact of the Afro-Arabian Plate with Eurasia around 17 million years ago (m.y.a.) is associated with profound changes in Miocene faunal communities. At or about this time, a hominoid appeared in East Africa that was anatomically quite different from the Proconsul species complex that had been endemic there for over 6 million years. These differences involved elements of occlusal design, thickness of molar enamel caps, and gnathic buttressing, which showed a general increase in robusticity. By the mid 1970s, this combination of features had come to be regarded as exclusively characteristic of australopithecines or their immediate ancestors. Thus the presence of a hominoid with thick enamel and robust maxillae at Fort Ternan seemed to provide the oldest evidence of hominids (Simons, 1968; Andrews and Tekkaya, 1976; Simons and Pilbeam, 1978). The later discovery and diagnosis of Australopithecus afarensis from Pliocene deposits in Ethiopia and Tanzania (Johanson et al., 1978; Johanson and White, 1979) tended to further strengthen the argument that an animal like Ramapithecus from East Africa and Indo-Pakistan was ancestral to the earliest undoubted hominids.

Hipparion species are important markers in faunal correlations. Their appearance is normally taken to define the boundary between the Miocene and Pliocene in continental deposits1. The genus is thought to have evolved in North America, probably around 12 million years ago2, and the spread of early, primitive Hipparion species to Eurasia has consequently been presumed to have occurred at this time, although it might have happened earlier if Hipparion older than 12 million years is dated in North America. The relative age of the faunas of the classic Siwalik deposits of north-west India and Pakistan is of considerable interest for the dating of the fossil primates Dryopithecus and Ramapithecus. The age of these primates is important because Ramapithecus has been recognized as the earliest probable hominid and it may lie in the direct line of human ancestry.

WOLPOFF1 has recently argued that the cranial capacity of the type specimen of Homo habilis2 from Olduvai Gorge, Tanzania (Olduvai hominid 7), is not sufficiently different from those of South African Australopithecus africanus to warrant placement in a separate species. He arrives at this conclusion by pooling the sets of observations from Olduvai and South Africa, calculating the mean and standard deviation of this “sample”, and showing that the sample coefficient of variation is not unduly high. He also shows that Olduvai hominid 7 falls only 2.03 standard deviations from the sample mean.

I SHOULD like to make a few points arising from the previous letter1. Much of the debate centres around the problem of species in palaeontology; how to define these, and how to assign new specimens to their appropriate taxon2. It is obvious that “the specimens representing the species make up the statistical universe”. The point which Wolpoff ignores is the manner in which individual specimens are assigned to “species”. In classifying fossils, due attention must be paid to variation within and between infraspecific populations, as well as to possible variation due to time2. The most important issue to decide in the evaluation of a new find is the species lineage (that is, a sequence of ancestral/descendant species populations) to which it belongs, and this requires some consideration of position with respect to infraspecific lineages (infraspecific lineages being sequences of ancestral/descendant infraspecific populations which are not isolated from others but which do have some time duration). Only when this decision has been made ought attention to be turned to classification at the species level, that is, to dividing up the evolving continuum and giving the arbitrary divisions binomina.

Day and Wood have very elegantly shown that three hominoid tali from the early Miocene of Kenya are functionally similar to those from the living pronograde quadrupedal African apes, Pan and Gorilla, and unlike modern bipedal man1. Two of the tali (CMH 145 from Songhor and CMH 147 from Rusinga) were described first by Maclnnes2 and later more fully by Le Gros Clark and Leakey3; Le Gros Clark subsequently described a second talus from Rusinga4. I have some tentative suggestions concerning their identification.