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 fossiliferous 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 taxonomic 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 dra...

Tropical South America has the highest plant diversity of any region today, but this richness is usually characterized as a geologically recent development (Neogene or Pleistocene). From caldera-lake beds exposed at Laguna del Hunco in Patagonia, Argentina, paleolatitude ∼47°S, we report 102 leaf species. Radioisotopic and paleomagnetic analyses indicate that the flora was deposited 52 million years ago, the time of the early Eocene climatic optimum, when tropical plant taxa and warm, equable climates reached middle latitudes of both hemispheres. Adjusted for sample size, observed richness exceeds that of any other Eocene leaf flora, supporting an ancient history of high plant diversity in warm areas of South America.

Policy aimed at conserving biodiversity has focused on species diversity. Loss of genetic diversity, however, can affect population persistence, evolutionary potential, and individual fitness. Although mammals are a well-studied taxonomic group, a comprehensive assessment of mammalian genetic diversity based on modern molecular markers is lacking. We examined published microsatellite data from populations of 108 mammalian species to evaluate background patterns of genetic variability across taxa and body masses. We tested for loss of genetic diversity at the population level by asking whether populations that experienced demographic threats exhibited lower levels of genetic diversity. We also evaluated the effect of ascertainment bias (a reduction in variability when microsatellite primers are transferred across species) on our assessment of genetic diversity. Heterozygosity did not vary with body mass across species ranging in size from shrews to whales. Differences across taxonomic groupings were noted at the highest level, between populations of marsupial and placental mammals. We documented consistently lower heterozygosity, however, in populations that had experienced demographic threats across a wide range of mammalian species. We also documented a significant (p = 0.01) reduction in heterozygosity as a result of ascertainment bias. Our results suggest that populations of both rare and common mammals are currently losing genetic diversity and that conservation efforts focused above the population level may fail to protect the breadth of persisting genetic diversity. Conservation policy makers may need to focus their efforts below the species level to stem further losses of genetic resources.Resumen: Las políticas de conservación de la biodiversidad tradicionalmente se han centrado en la diversidad de especies. Sin embargo, la pérdida de diversidad genética puede impactar al potencial de persistencia y evolutivo, así como a la adaptabilidad individual. Aunque los mamíferos son un grupo taxonómico bien estudiado, se carece de una evaluación integral de la diversidad genética de mamíferos basada en marcadores moleculares. Examinamos datos publicados de microsatélites de poblaciones de 108 especies de mamíferos para evaluar los patrones de variabilidad genética entre los taxa y masas corporales. Probamos la pérdida de variabilidad en el nivel poblacional preguntando si las poblaciones que experimentaron amenazas demográficas exhibieron menores niveles de diversidad genética. También evaluamos el impacto del sesgo de determinación (una reducción en la variabilidad cuando los iniciadores de microsatélites son transferidos a otras especies) sobre nuestro análisis de diversidad genética. La heterocigosidad no varió con la masa corporal en especies que variaron en tamaño desde musarañas hasta ballenas. Las diferencias entre grupos taxonómicos se notaron en el nivel más alto, entre poblaciones mamíferos marsupiales y placentarios. Sin embargo, en un amplio rango de especies de mamíferos consistentemente documentamos ...

This study uses stable isotope variation within individual Mio-Pliocene paleosols to investigate subkilometer-scale phytogeography of late Miocene vegetation change in southeast Asia between ca. 8.1 and 5 Ma, a time interval that coincides with dramatic global vegetation change. We examine trends through time in the distribution of low-latitude grasses (C 4 plants) and forest (C 3 plants) on Indo-Gangetic fl oodplains using carbon (δ 13 C) and oxygen isotopic (δ 18 O) values in buried soil carbonates in Siwalik Series sediments exposed in the Rohtas Anticline, northcentral Pakistan. Revised, high-resolution magnetostratigraphy and a new 40 Ar/ 39 Ar date provide improved age control for the 2020 m Rohtas section. Carbon isotope results capture lateral variability of C 3 versus C 4 plants at fi ve stratigraphic levels, R11 (8.0 Ma), R15 (6.74-6.78 Ma), R23 (5.78 Ma), R29 (4.8-4.9 Ma), and upper boundary tuff (UBT; 2.4 Ma), using detailed sampling of paleosols traceable laterally over hundreds of meters. Paleosols and the contained isotopic results can be assigned to three different depositional contexts within the fl uvial sediments: channel fi ll, crevasse-splay, and fl oodplain environments. δ 13 C results show that near the beginning (8.0 Ma) and after (4.0 Ma) the period of major ecological change, vegetation was homogeneously C 3 or C 4 , respectively, regardless of paleo-landscape position. In the intervening period, there is a wide range of values overall, with C 4 grasses fi rst invading the drier portions of the system (fl oodplain surfaces) and C 3 plants persisting in moister settings, such as topographically lower channel swales. Although abrupt on a geologic timescale, changes in abundance of C 4 plants are modest (~2% per 100,000 yr) compared to rates of vegetation turnover in response to glacial and interglacial climate changes in the Quaternary. Earlier research documented a sharply defi ned C 3 to C 4 transition in Pakistan between 8.1 and 5.0 Ma, based on vertical sampling, but this higher-resolution study reveals a more gradual transition between 8.0 and 4.5 Ma in which C 3 and C 4 plants occupied different subenvironments of the Siwalik alluvial plain.δ 18 O values as well as δ 13 C values of soil carbonate increase up section at Rohtas, similar to isotope trends in other paleosol records from the region. Spatially, however, there is no correlation between δ 13 C and δ 18 O values at most stratigraphic levels. This implies that the changes in soil hydrology brought about by the shift from forest to grassland (i.e., an increase in average soil evaporation) did not produce the shift through time in δ 18 O values. We interpret the trend toward heavier soil carbonate δ 18 O values as a response to changes in external climatic factors such as a net decrease in rainfall over the past 9 Ma.

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