ABSTRACT Extensive fields of large boulders are common around the base of hills in the Atacama De... more ABSTRACT Extensive fields of large boulders are common around the base of hills in the Atacama Desert. How these boulders are transported from nearby hillslopes is unclear given the lack of rainfall of the region. Here we document the central role of seismicity, not runoff, in transporting and smoothing > 1 ton boulders all across the hyperarid core of the Atacama Desert. The generally granitoid boulders emerge as corestones on hillslopes at an erosion rate of 0.1-1 m Ma− 1. Thereafter, physical and cosmogenic isotopic evidence suggests that boulders slide and bounce rather than roll down hills and onto adjacent flats. In the transport process, the largest boulders are split and the smaller ones are weathered to grus, narrowing average boulder mass to ~ 2 tons (< 1 m3). At the base of hills, the boulders bunch together and rub during the frequent earthquakes in the region, producing distinctive smoothing around boulder mid-sections, and silt moats around the boulder bases. Our measurements show a strong correlation between boulder field density and rubbing, and only when the density exceeds 60-70% does rubbing become common. Except for slow removal by rubbing, the boulders seem to undergo no further erosion while in the flats. Exposure times for some boulders are > 12 Ma, making them among the oldest continuously exposed features on the Earth. Boulder rubbing is just one geologic feature among many in the Atacama that underscore the role that seismicity probably plays in shaping landscapes of the waterless worlds of the solar system.
The Zada basin of southwestern Tibet is the largest late Cenozoic basin on the Tibetan plateau. T... more The Zada basin of southwestern Tibet is the largest late Cenozoic basin on the Tibetan plateau. The basin developed above the Tethyan Himalayan sequence and is located between major detachment faults to the northwest and southeast, the Ayi Shan Mountains along the dextral Karakoram fault to the northeast, and a major newly recognized dextral strike slip fault to the southwest. However, Zada basin fill is presently flat-lying, buttressing paleotopography along its northern and southern margins and not spatially associated with the South Tibetan detachment system. The Zada basin records one major pulse of accommodation creation as indicated by basal debris flows and fluvial pebble conglomerates. Paleocurrent data show transverse flow along basin margins and axial NW-ward flow along the basin center. A period of lacustrine sedimentation followed, with deposition of multiple, upward coarsening calcareous clay - fine sand para-sequences within an overall progradational sequence. The sand...
ABSTRACT Large mid-Tertiary sedimentary basins at 4.4 km elevation in the north-central Lhasa ter... more ABSTRACT Large mid-Tertiary sedimentary basins at 4.4 km elevation in the north-central Lhasa terrane archive the history of environments and paleoelevation in the central part of the Tibetan Plateau. In the Nyima basin, more than 3 km of strongly shortened fluvial, alluvial fan, and lacustrine sediment accumulated along the north flank of a major north-verging fold-thrust belt. The maximum age of the succession is 40 Ma, based on U-Pb ages of detrital zircons. Biotite 40Ar/39Ar ages from reworked tuffs in the lower third of the succession indicate deposition at 25 to 26 Ma. Provenance and paleocurrent data require sediment source areas to the south in the fold-thrust belt. d18O values from lacustrine marls and fossil shell material are strongly negative (-10 to -14); if unaltered by diagenesis these values suggest paleoelevations on the order of 4 km. Roughly 50 km to the north, in the Muggar Kangri Range, thick nonmarine strata record a wide variety of depositional environments, including eolian dune facies. Unlike the Nyima basin, the Muggar Kangri basin reflects longitudinal eastward flowing paleodrainage. Eolian dune facies yield generally eastward paleowind directions. Sediment source areas lay toward the north, in thrust-faulted ranges lying within the southern Qiangtang terrane. Regional correlations based on lithostratigraphy suggest that the upper part of the Muggar Kangri basin fill is roughly the same age as the Nyima basin fill. Taken together, the new geochronologic, oxygen isotopic, and sedimentary facies data indicate that (1) Nyima basin fill is younger than widely distributed Eocene-Oligocene strata in north-central Tibet, challenging models that predict a systematic northward younging in upper crustal shortening and basin development and (2) the central part of the Plateau was high (>4 km) and dry by mid-Tertiary time.
Pluvial lakes in Argentina provide a unique record of climate change during the Late Quaternary. ... more Pluvial lakes in Argentina provide a unique record of climate change during the Late Quaternary. Two lake systems were studied as part of an effort to understand major climatic changes during the Last Glacial Maximum (LGM: 24-18 ka) and the following deglaciation (18-13 ka). Today, both of the studied regions are arid, and the lake basins contain much smaller lakes than in the past. Laguna Cari-Laufquen is located at 41°S and the modern basin is occupied by two lakes: Cari-Laufquen Grande and Chica. Preserved shorelines and sediments show these two lakes rose and merged multiple times during the Late Quaternary. Initial radiocarbon and U-series dates show the lake was the highest during the LGM, with several smaller, more recent lake oscillations. The second lake system in this study is Laguna Bebedero, located at 33°S in western Argentina. Previous studies show the highest shorelines date to 23-16,000 yrs BP. Our new radiocarbon dates help constrain the timing of the highstands, al...
We analyzed modern meteoric water (n = 170) and soil carbonate (n = 300) from southern and centra... more We analyzed modern meteoric water (n = 170) and soil carbonate (n = 300) from southern and central Tibet in order to establish an isotopic framework for reconstructions of paleoelevation of the Tibetan Plateau. The oxygen isotopic composition of modern meteoric waters is not a simple function of elevation---as assumed by some previous reconstructions of paleoelevation---but increases markedly with distance north of the Himalayan massif (~3 per mil/degree latitude; r2 = 0.6). This decrease reflects the interplay of monsoonal moisture sources in the south with northern moisture sources possibly recycled from local lakes, bogs, and soils. The oxygen isotopic value of modern soil carbonate shows significant scatter due to the effects of evaporation, but the most negative, least evaporated oxygen isotopic values also increase northwards, following the pattern of meteoric waters but at a lower slope of 1.0-1.5 per mil/degree latitude. The latitudinal differences in the modern soil and wat...
Coeval Oligo-Miocene basins along the Bangong and Yarlung suture zones (BSZ and YSZ) in Tibet rec... more Coeval Oligo-Miocene basins along the Bangong and Yarlung suture zones (BSZ and YSZ) in Tibet record drastically different environmental conditions, tectonic processes, and possibly paleoelevations. The Nima and Lunpola basins formed in a contractile tectonic setting during late Oligocene reactivation of the BSZ, and filled with alluvial, fluvial, and lacustrine facies that were strongly influenced by boreal or alpine dry climate and high paleoelevation (>4.6 km). At the same time, the Kailas basin developed along the YSZ approximately 450 km to the west-southwest. The Kailas Formation is >2500 m thick, and rests in buttress unconformity upon ca. 67 Ma silicic volcanic rocks, which are intruded by 55 Ma granite. U-Pb ages from tuffs and detrital zircons in the Kailas Formation indicate deposition at 26-23 Ma, possibly continuing into mid- Miocene time. Unlike the strongly oxidized, evaporitic, and paleosol carbonate-rich deposits of Nima basin, the Kailas basin is dominated by...
ABSTRACT Here we explore a variety of isotopic systems to reconstruct paleoatitude in southern Ti... more ABSTRACT Here we explore a variety of isotopic systems to reconstruct paleoatitude in southern Tibet and the central Andes. A multi-system approach is essential since the necessary mineral archives are not always available, and because diagenetic resetting of some systems clearly occurs. In the central Andes at ~24°S, carbonate is rare due to hyperaridity, and where present, evaporation in soils and lakes completely alters the primary meteoric signal. Waters of hydration of volcanic glass are a much more promising target in this region given the prevalence of volcanic tuffs. We have analyzed the δD value of a suite of modern and ancient glasses back to 34 Ma that show little change in elevation in the western Cordillera of the Andes. By contrast, the eastern Cordillera of the Andes rose in the last 15 Ma. This pattern is consistent with gradual eastward propagation of the whole orogen at this latitude, including the trench, forearc, magmatic arc, and foreland. The paleoaltimetry of Tibet poses quite different challenges to those in South America. Volcanic glass archives are so far unavailable, whereas carbonate archives are common but in some cases diagenetically reset. We have focused on records of conventional δ18O values and clumped isotope thermometry. One must treat both archives with great caution due to resetting, especially clumped isotopes. Available evidence suggests that southern Tibet has been near current elevations since the early Miocene. For the pre- Miocene we present new isotopic/paleosol records found along the suture zone of India and Asia that we believe partly chronicle the rise of the suture zone from near sea-level to >4000 m today.
Two large paleolakes (33,000 and 60,000 km2) occupied dry basins on the southern Bolivian Altipla... more Two large paleolakes (33,000 and 60,000 km2) occupied dry basins on the southern Bolivian Altiplano during the Late Glacial, providing evidence of dramatic changes in low-latitude moisture. It is now apparent that the Tauca (18.1-14.1 ka) and Coipasa (13-11 ka) lake cycles are part of a regional wet interval, the Central Andean Pluvial Event (CAPE). Proposed driving mechanisms for CAPE include changes in: summer solar insolation, Pacific SST gradients (ENSO variability), Atlantic SST gradients (the Younger Dryas and Heinrich I), and moisture levels in the eastern lowlands. The region impacted by CAPE may extend from 10 to 26°S. The Southern Altiplano (18-22°S) is at the center of this region. Regional climate histories, however, highlight existing uncertainties and contradictions about the timing, magnitude, and synchrony of the CAPE both across the region and within Altiplano lake basins. Are differing conclusions about the timing and mechanisms of central Andean climate change rel...
The connection between global climate and regional climate in the southern hemisphere tropics and... more The connection between global climate and regional climate in the southern hemisphere tropics and subtropics is poorly understood. On the Bolivian Altiplano, a new unified lake history based on evidence from both naturally exposed shoreline deposits and sediment cores is coupled with a hydrologic budget model to yield a record of precipitation changes on the southern Bolivian Altiplano over the last 130 ka. Ten lake cycles and two major trends are apparent in the Altiplano precipitation record: 1) the Altiplano was relatively dry during the global cold interval between 80 and 20 ka; and 2) each of ten precipitation increases coincides with a cold event in the north Atlantic. This long range, high-resolution lake record allows us to test possible links between central Andean climate and global climate events such as: 1) changes over glacial-interglacial cycles; 2) seasonal insolation over land; 3) Pacific sea surface temperature (SST) gradients; and 4) Atlantic thermohaline circulati...
The Atacama Desert of Northern Chile is often viewed as stable and hyperarid over many millions o... more The Atacama Desert of Northern Chile is often viewed as stable and hyperarid over many millions of years. Among the primary lines of evidence for both a landscape and climate that has remained stable and hyperarid for >10 Ma are extremely high cosmogenic nuclide concentrations from ancient geomorphic surfaces. Here, we present concentrations of the cosmogenic nuclides 10Be, 26Al and 21Ne in boulders from the broadest portion of the Atacama Desert, where the modern Andean rainshadow is most pronounced. These boulders occur in groups of hundreds to thousands, are up to two meters in diameter, and rest independent from each other on the surface within an area having definite boundaries (up to 0.5 km in extent). These 'Atacama boulder fields" are unique but common features in the driest portions of the Atacama. Modern mass wasting features containing boulders are not present here and boulder fields are relicts of a time when the Atacama experienced significantly more geomorp...
Since 2000, significant collections of Latest Miocene hominin fossils have been recovered from Ch... more Since 2000, significant collections of Latest Miocene hominin fossils have been recovered from Chad, Kenya, and Ethiopia. These fossils have provided a better understanding of earliest hominin biology and context. Here, we describe five hominin teeth from two periods (ca. 5.4 Million-years-ago and ca. 6.3 Ma) that were recovered from the Adu-Asa Formation in the Gona Paleoanthropological Research Project area in the Afar, Ethiopia that we assign to either Hominina, gen. et sp. indet. or Ardipithecus kadabba. These specimens are compared with extant African ape and other Latest Miocene and Early Pliocene hominin teeth. The derived morphology of the large, non-sectorial maxillary canine and mandibular third premolar links them with later hominins and they are phenetically distinguishable and thus phyletically distinct from extant apes.
The Gona Paleoanthropological Research Project (GPRP) area includes many rich fossil localities t... more The Gona Paleoanthropological Research Project (GPRP) area includes many rich fossil localities that are of great consequence to the study of human evolution. Genetic estimates of the divergence between human and chimpanzee lineages indicate that this split happened between 5 and 7 Mya. The sedimentary deposits at Gona range in age from .15 Ma to 4.5 Ma at the base
Soil samples taken from a 4500-m elevational transect just south of the Tropic of Capricorn (−24°... more Soil samples taken from a 4500-m elevational transect just south of the Tropic of Capricorn (−24°S) all yielded culturable bacteria on R2A agar (1, 2), including samples from elevations of absolute desert that have not harbored plant life for a million years or more. Four of our ...
... Late Pleistocene C 4 Plant Dominance and Summer Rainfall in the Southwestern United States fr... more ... Late Pleistocene C 4 Plant Dominance and Summer Rainfall in the Southwestern United States from Isotopic Study of ... of climate and C 4 plant abundance in the southwestern United States during the last glaciation were evaluated from isotopic study of herbivore tooth ...
ABSTRACT Extensive fields of large boulders are common around the base of hills in the Atacama De... more ABSTRACT Extensive fields of large boulders are common around the base of hills in the Atacama Desert. How these boulders are transported from nearby hillslopes is unclear given the lack of rainfall of the region. Here we document the central role of seismicity, not runoff, in transporting and smoothing > 1 ton boulders all across the hyperarid core of the Atacama Desert. The generally granitoid boulders emerge as corestones on hillslopes at an erosion rate of 0.1-1 m Ma− 1. Thereafter, physical and cosmogenic isotopic evidence suggests that boulders slide and bounce rather than roll down hills and onto adjacent flats. In the transport process, the largest boulders are split and the smaller ones are weathered to grus, narrowing average boulder mass to ~ 2 tons (< 1 m3). At the base of hills, the boulders bunch together and rub during the frequent earthquakes in the region, producing distinctive smoothing around boulder mid-sections, and silt moats around the boulder bases. Our measurements show a strong correlation between boulder field density and rubbing, and only when the density exceeds 60-70% does rubbing become common. Except for slow removal by rubbing, the boulders seem to undergo no further erosion while in the flats. Exposure times for some boulders are > 12 Ma, making them among the oldest continuously exposed features on the Earth. Boulder rubbing is just one geologic feature among many in the Atacama that underscore the role that seismicity probably plays in shaping landscapes of the waterless worlds of the solar system.
The Zada basin of southwestern Tibet is the largest late Cenozoic basin on the Tibetan plateau. T... more The Zada basin of southwestern Tibet is the largest late Cenozoic basin on the Tibetan plateau. The basin developed above the Tethyan Himalayan sequence and is located between major detachment faults to the northwest and southeast, the Ayi Shan Mountains along the dextral Karakoram fault to the northeast, and a major newly recognized dextral strike slip fault to the southwest. However, Zada basin fill is presently flat-lying, buttressing paleotopography along its northern and southern margins and not spatially associated with the South Tibetan detachment system. The Zada basin records one major pulse of accommodation creation as indicated by basal debris flows and fluvial pebble conglomerates. Paleocurrent data show transverse flow along basin margins and axial NW-ward flow along the basin center. A period of lacustrine sedimentation followed, with deposition of multiple, upward coarsening calcareous clay - fine sand para-sequences within an overall progradational sequence. The sand...
ABSTRACT Large mid-Tertiary sedimentary basins at 4.4 km elevation in the north-central Lhasa ter... more ABSTRACT Large mid-Tertiary sedimentary basins at 4.4 km elevation in the north-central Lhasa terrane archive the history of environments and paleoelevation in the central part of the Tibetan Plateau. In the Nyima basin, more than 3 km of strongly shortened fluvial, alluvial fan, and lacustrine sediment accumulated along the north flank of a major north-verging fold-thrust belt. The maximum age of the succession is 40 Ma, based on U-Pb ages of detrital zircons. Biotite 40Ar/39Ar ages from reworked tuffs in the lower third of the succession indicate deposition at 25 to 26 Ma. Provenance and paleocurrent data require sediment source areas to the south in the fold-thrust belt. d18O values from lacustrine marls and fossil shell material are strongly negative (-10 to -14); if unaltered by diagenesis these values suggest paleoelevations on the order of 4 km. Roughly 50 km to the north, in the Muggar Kangri Range, thick nonmarine strata record a wide variety of depositional environments, including eolian dune facies. Unlike the Nyima basin, the Muggar Kangri basin reflects longitudinal eastward flowing paleodrainage. Eolian dune facies yield generally eastward paleowind directions. Sediment source areas lay toward the north, in thrust-faulted ranges lying within the southern Qiangtang terrane. Regional correlations based on lithostratigraphy suggest that the upper part of the Muggar Kangri basin fill is roughly the same age as the Nyima basin fill. Taken together, the new geochronologic, oxygen isotopic, and sedimentary facies data indicate that (1) Nyima basin fill is younger than widely distributed Eocene-Oligocene strata in north-central Tibet, challenging models that predict a systematic northward younging in upper crustal shortening and basin development and (2) the central part of the Plateau was high (>4 km) and dry by mid-Tertiary time.
Pluvial lakes in Argentina provide a unique record of climate change during the Late Quaternary. ... more Pluvial lakes in Argentina provide a unique record of climate change during the Late Quaternary. Two lake systems were studied as part of an effort to understand major climatic changes during the Last Glacial Maximum (LGM: 24-18 ka) and the following deglaciation (18-13 ka). Today, both of the studied regions are arid, and the lake basins contain much smaller lakes than in the past. Laguna Cari-Laufquen is located at 41°S and the modern basin is occupied by two lakes: Cari-Laufquen Grande and Chica. Preserved shorelines and sediments show these two lakes rose and merged multiple times during the Late Quaternary. Initial radiocarbon and U-series dates show the lake was the highest during the LGM, with several smaller, more recent lake oscillations. The second lake system in this study is Laguna Bebedero, located at 33°S in western Argentina. Previous studies show the highest shorelines date to 23-16,000 yrs BP. Our new radiocarbon dates help constrain the timing of the highstands, al...
We analyzed modern meteoric water (n = 170) and soil carbonate (n = 300) from southern and centra... more We analyzed modern meteoric water (n = 170) and soil carbonate (n = 300) from southern and central Tibet in order to establish an isotopic framework for reconstructions of paleoelevation of the Tibetan Plateau. The oxygen isotopic composition of modern meteoric waters is not a simple function of elevation---as assumed by some previous reconstructions of paleoelevation---but increases markedly with distance north of the Himalayan massif (~3 per mil/degree latitude; r2 = 0.6). This decrease reflects the interplay of monsoonal moisture sources in the south with northern moisture sources possibly recycled from local lakes, bogs, and soils. The oxygen isotopic value of modern soil carbonate shows significant scatter due to the effects of evaporation, but the most negative, least evaporated oxygen isotopic values also increase northwards, following the pattern of meteoric waters but at a lower slope of 1.0-1.5 per mil/degree latitude. The latitudinal differences in the modern soil and wat...
Coeval Oligo-Miocene basins along the Bangong and Yarlung suture zones (BSZ and YSZ) in Tibet rec... more Coeval Oligo-Miocene basins along the Bangong and Yarlung suture zones (BSZ and YSZ) in Tibet record drastically different environmental conditions, tectonic processes, and possibly paleoelevations. The Nima and Lunpola basins formed in a contractile tectonic setting during late Oligocene reactivation of the BSZ, and filled with alluvial, fluvial, and lacustrine facies that were strongly influenced by boreal or alpine dry climate and high paleoelevation (>4.6 km). At the same time, the Kailas basin developed along the YSZ approximately 450 km to the west-southwest. The Kailas Formation is >2500 m thick, and rests in buttress unconformity upon ca. 67 Ma silicic volcanic rocks, which are intruded by 55 Ma granite. U-Pb ages from tuffs and detrital zircons in the Kailas Formation indicate deposition at 26-23 Ma, possibly continuing into mid- Miocene time. Unlike the strongly oxidized, evaporitic, and paleosol carbonate-rich deposits of Nima basin, the Kailas basin is dominated by...
ABSTRACT Here we explore a variety of isotopic systems to reconstruct paleoatitude in southern Ti... more ABSTRACT Here we explore a variety of isotopic systems to reconstruct paleoatitude in southern Tibet and the central Andes. A multi-system approach is essential since the necessary mineral archives are not always available, and because diagenetic resetting of some systems clearly occurs. In the central Andes at ~24°S, carbonate is rare due to hyperaridity, and where present, evaporation in soils and lakes completely alters the primary meteoric signal. Waters of hydration of volcanic glass are a much more promising target in this region given the prevalence of volcanic tuffs. We have analyzed the δD value of a suite of modern and ancient glasses back to 34 Ma that show little change in elevation in the western Cordillera of the Andes. By contrast, the eastern Cordillera of the Andes rose in the last 15 Ma. This pattern is consistent with gradual eastward propagation of the whole orogen at this latitude, including the trench, forearc, magmatic arc, and foreland. The paleoaltimetry of Tibet poses quite different challenges to those in South America. Volcanic glass archives are so far unavailable, whereas carbonate archives are common but in some cases diagenetically reset. We have focused on records of conventional δ18O values and clumped isotope thermometry. One must treat both archives with great caution due to resetting, especially clumped isotopes. Available evidence suggests that southern Tibet has been near current elevations since the early Miocene. For the pre- Miocene we present new isotopic/paleosol records found along the suture zone of India and Asia that we believe partly chronicle the rise of the suture zone from near sea-level to >4000 m today.
Two large paleolakes (33,000 and 60,000 km2) occupied dry basins on the southern Bolivian Altipla... more Two large paleolakes (33,000 and 60,000 km2) occupied dry basins on the southern Bolivian Altiplano during the Late Glacial, providing evidence of dramatic changes in low-latitude moisture. It is now apparent that the Tauca (18.1-14.1 ka) and Coipasa (13-11 ka) lake cycles are part of a regional wet interval, the Central Andean Pluvial Event (CAPE). Proposed driving mechanisms for CAPE include changes in: summer solar insolation, Pacific SST gradients (ENSO variability), Atlantic SST gradients (the Younger Dryas and Heinrich I), and moisture levels in the eastern lowlands. The region impacted by CAPE may extend from 10 to 26°S. The Southern Altiplano (18-22°S) is at the center of this region. Regional climate histories, however, highlight existing uncertainties and contradictions about the timing, magnitude, and synchrony of the CAPE both across the region and within Altiplano lake basins. Are differing conclusions about the timing and mechanisms of central Andean climate change rel...
The connection between global climate and regional climate in the southern hemisphere tropics and... more The connection between global climate and regional climate in the southern hemisphere tropics and subtropics is poorly understood. On the Bolivian Altiplano, a new unified lake history based on evidence from both naturally exposed shoreline deposits and sediment cores is coupled with a hydrologic budget model to yield a record of precipitation changes on the southern Bolivian Altiplano over the last 130 ka. Ten lake cycles and two major trends are apparent in the Altiplano precipitation record: 1) the Altiplano was relatively dry during the global cold interval between 80 and 20 ka; and 2) each of ten precipitation increases coincides with a cold event in the north Atlantic. This long range, high-resolution lake record allows us to test possible links between central Andean climate and global climate events such as: 1) changes over glacial-interglacial cycles; 2) seasonal insolation over land; 3) Pacific sea surface temperature (SST) gradients; and 4) Atlantic thermohaline circulati...
The Atacama Desert of Northern Chile is often viewed as stable and hyperarid over many millions o... more The Atacama Desert of Northern Chile is often viewed as stable and hyperarid over many millions of years. Among the primary lines of evidence for both a landscape and climate that has remained stable and hyperarid for >10 Ma are extremely high cosmogenic nuclide concentrations from ancient geomorphic surfaces. Here, we present concentrations of the cosmogenic nuclides 10Be, 26Al and 21Ne in boulders from the broadest portion of the Atacama Desert, where the modern Andean rainshadow is most pronounced. These boulders occur in groups of hundreds to thousands, are up to two meters in diameter, and rest independent from each other on the surface within an area having definite boundaries (up to 0.5 km in extent). These 'Atacama boulder fields" are unique but common features in the driest portions of the Atacama. Modern mass wasting features containing boulders are not present here and boulder fields are relicts of a time when the Atacama experienced significantly more geomorp...
Since 2000, significant collections of Latest Miocene hominin fossils have been recovered from Ch... more Since 2000, significant collections of Latest Miocene hominin fossils have been recovered from Chad, Kenya, and Ethiopia. These fossils have provided a better understanding of earliest hominin biology and context. Here, we describe five hominin teeth from two periods (ca. 5.4 Million-years-ago and ca. 6.3 Ma) that were recovered from the Adu-Asa Formation in the Gona Paleoanthropological Research Project area in the Afar, Ethiopia that we assign to either Hominina, gen. et sp. indet. or Ardipithecus kadabba. These specimens are compared with extant African ape and other Latest Miocene and Early Pliocene hominin teeth. The derived morphology of the large, non-sectorial maxillary canine and mandibular third premolar links them with later hominins and they are phenetically distinguishable and thus phyletically distinct from extant apes.
The Gona Paleoanthropological Research Project (GPRP) area includes many rich fossil localities t... more The Gona Paleoanthropological Research Project (GPRP) area includes many rich fossil localities that are of great consequence to the study of human evolution. Genetic estimates of the divergence between human and chimpanzee lineages indicate that this split happened between 5 and 7 Mya. The sedimentary deposits at Gona range in age from .15 Ma to 4.5 Ma at the base
Soil samples taken from a 4500-m elevational transect just south of the Tropic of Capricorn (−24°... more Soil samples taken from a 4500-m elevational transect just south of the Tropic of Capricorn (−24°S) all yielded culturable bacteria on R2A agar (1, 2), including samples from elevations of absolute desert that have not harbored plant life for a million years or more. Four of our ...
... Late Pleistocene C 4 Plant Dominance and Summer Rainfall in the Southwestern United States fr... more ... Late Pleistocene C 4 Plant Dominance and Summer Rainfall in the Southwestern United States from Isotopic Study of ... of climate and C 4 plant abundance in the southwestern United States during the last glaciation were evaluated from isotopic study of herbivore tooth ...
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