John C. Barry

A 16-Ma record of paleodiet using carbon and oxygen isotopes in fossil teeth from Pakistan

Abstract 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.

A biostratigraphic zonation of the middle and upper siwaliks of the potwar plateau of Northern Pakistan

Abstract Two biostratigraphic reference sections are designated for the middle and upper Siwalik formations of northern Pakistan. The stratigraphic ranges of 41 mammalian taxa are established in the reference sections and the two sections are correlated to each other and to the standard Magnetic Polarity Time Scale by the magnetic-polarity stratigraphy. The resulting stratigraphic and magnetostratigraphic framework is used to define four contiguous biostratigraphic interval-zones. The proposed interval-zones are bounded by five important faunal events which are identified in the reference sections. The four proposed interval-zones and the approximate ages in the reference sections of their lower and upper boundaries are: (1) the “ Hipparion s.l.” Interval-Zone 7.4–9.5 m.y. B.P.; (2) the Selenoportax lydekkeri Interval-Zone 5.3–7.4 m.y. B.P.; (3) the Hexaprotodon sivalensis Interval-Zone 5.3-2.9 m.y. B.P.; and (4) the Elephas planifrons Interval-Zone 2.9-1.5 m.y. B.P. The paleomagnetic and biostratigraphic evidence indicates that the Tatrot Beds, from which Pilgrim developed his “Tatrot Faunal Zone”, are between 2.5 and 3.4 m.y. B.P., with a preferred maximum age of 2.9 m.y. B.P. The biostratigraphic evidence indicates the Sethi Nagri locality (Y311)—the primary source of Pilgrims “Nagri Faunal Zone”— is in the “ Hipparion s.l.” Interval-Zone. The paleomagnetic evidence suggests an approximate age of 9 m.y. B.P. A major faunal event at 9.5 m.y. B.P. introduced equids, suids, and large giraffes from Eurasia into the Indain subcontinent. A second, more diffuse faunal event between 5.3 and 2.9 m.y. B.P. introduced several African taxa as well as Equus and cervids from Eurasia.

Ecological changes in Miocene mammalian record show impact of prolonged climatic forcing

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, C4 savannah replaced C3 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 C4 plants and persisted for >1 myr during the vegetation transition. The few lineages that persisted through the vegetation transition show isotopic enrichment of δ13C values over time. These results are evidence for long-term climatic forcing of vegetation structure and mammalian ecological diversity at the subcontinental scale.

Geology and palaeontology of Neogene strata of Pakistan

A joint study of the Potwar Plateau of Pakistan is yielding abundant material for stratigraphic and palaeontological reassessment.

Neogene palaeontology and geochronology of the Baringo Basin, Kenya

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.

Key Biostratigraphic Events in the Siwalik Sequence

Miocene movements of crustal plates brought about fundamental changes in the oceans by fragmenting the Tethys Seaway and further isolating the Atlantic, Indian, and Pacific basins. Although controversial in the details of interpretation, the resulting paleoceanographic and tectonic events have been linked to global climate (Kennett et al., 1985; Woodruff, 1985; Hodell et al., 1986) and, largely through their effects on climate, can be seen to have had a far-reaching influence on the plants and animals of the Miocene.

The earliest occurrence ofSivapithecus from the middle Miocene Chinji Formation of Pakistan

Abstract 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.

Probing DNA Replication Mechanisms with the T4 Bacteriophage In Vitro System

We have previously reported the development of a multienzyme in vitro DNA replication system which replicates double-stranded (DS) DNA templates efficiently. This system consists of six highly purified bacteriophage T4-encoded proteins, the products of genes 32, 41, 43, 44, 45, and 62 (Morris et al. 1975; Alberts et al. 1975, 1977). Each of these proteins has been shown to be essential for DNA replication in vivo (Epstein et al. 1964). An amber mutation in any of these genes results in a phenotype showing very little or no DNA synthesis (Warner and Hobbs 1967), even though adequate deoxyriboand ribonucleoside triphosphate levels are maintained (Mathews 1972). Additionally, temperature-sensitive mutants have been isolated in genes 32, 41, 43, and 45 which cease DNA replication immediately upon transfer to the restrictive temperature (Riva et al. 1970; Curtis and Alberts 1976). From such in vivo data, each of the above proteins is expected to function directly at a replication fork and, therefore, to be an important component of any T4 in vitro replication system. Our reconstructed in vitro system, in fact, requires each of these six proteins, as previously shown (Morris et al. 1975; Alberts et al. 1975, 1977). In addition, a seventh T4-encoded protein, which has recently been isolated and purified from T4-infected lysates, is shown to have an essential role in the in vitro DNA replication process (see below). It has been our goal to dissect and reconstruct the T4-encoded replication apparatus in order to understand the protein-protein and protein-DNA interactions generally involved in DNA replication. We wish to obtain a static picture of the architecture of a replication fork (including the arrangement of the multienzyme complex which functions there), as well as a dynamic picture of the events that accompany D N A polymerization. Heretofore much of the work has, of necessity, focused on the isolation and purification of the different replication proteins and on a search for separate, intrinsic protein activities. Recent work from this laboratory has been directed toward understanding the following three major aspects of the in vitro DNA synthesis catalyzed by the complete T4 DNA replication system: (1) How do the T4 proteins interact to initiate de novo synthesis of DNA strands, and what is the nature of the primer involved? (2) Does the rate of replication on duplex templates obtained in vitro approach the rate obtained in vivo, and is the energy of ATP hydrolysis utilized to drive the strand-displacement reaction? (3) How faithful is in vitro template copying, and how is this fidelity generated? After a brief review of the proteins that comprise the in vitro replication system, the status of these three aspects of our research is discussed in the order indicated.

The Siwaliks of Pakistan: time and faunas in a Miocene terrestrial setting

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