Chronological overlap between humans and megafauna in Sahul (Pleistocene Australia–New Guinea): A review of the evidence

Over 60 faunal species disappeared from the Australian continent during the Middle–Late Pleistocene. Most of these animals were large to gigantic marsupials, birds and reptiles. A terminal extinction date of 46.4 kyr has been proposed for the megafauna, with all sites containing younger fossil megafauna dismissed by some researchers because of questions over stratigraphic integrity or chronologies. The timing of the extinctions is argued to be broadly coincident with estimates of first colonization of the continent by modern humans, and explanatory extinction models involving humans have subsequently gained currency. However there is considerable evidence to suggest that in some parts of the continent, people and some species of megafauna may have co-existed well beyond 46.4 kyr. In other places, such as Tasmania and the north of the continent, there is no known record of a human–megafauna temporal overlap. A review of the available evidence indicates that only 13 species of megafauna were extant on human arrival in Australia. The archaeology of this period indicates that rather than a focus on big game hunting or ‘firestick farming’, it was characterized by regional variability in subsistence strategies consistent with the range of environmental zones. At the present time there is no substantive argument for a terminal extinction date of 46.4 kyr, the current evidence indicating that there is no specific time period that correlates to any single mass extinction event. On the basis of available evidence arguments for either human or climatic causation are entirely circumstantial and implicitly require acceptance of many unproven assumptions. Claims to have eliminated climate as a primary driver are premature and the recent focus on delivering ‘proof’ of human causation in Pleistocene faunal extinctions diverts attention from achieving a better understanding of the differential impacts of climate change and short term climatic flux in a land of environmental extremes.     

Climate,environment, and humans in North America’s Great Basin during the Younger Dryas, 12,900–11,600 calendar years ago

Global climate change associated with the onset of the Younger Dryas chronozone affected different regions of the northern hemisphere in different ways. In the Great Basin of western North America, the effect was positive for human populations. Relatively cool temperatures causing effectively wetter conditions filled some pluvial basins with shallow but permanent lakes and other basins with well-watered marshes or meadows. Vegetation communities dominated by sagebrush and grasses promoted healthy and diverse animal populations. Ten archaeological sites from the region have been dated to the Younger Dryas chronozone. Evidence from these sites indicates that Paleoindians with skull shapes and mitochondrial DNA similar to modern western North American Indians occupied the region. These early humans produced a material culture characterized predominantly by large stemmed bifacial points, although one site contained a small fluted point. Curated tool forms and technological activities represented in analyzed lithic assemblages suggest a highly mobile settlement strategy, and redundant short-term occupations of sites indicate frequent and long-distance residential moves across territories spanning distances of up to 400 km. Paleoindian subsistence pursuits focused on artiodactyls (primarily mule deer, bighorn sheep, and pronghorn antelope), leporids (chiefly jackrabbits), birds (sage grouse and waterfowl), insects (grasshoppers), and possibly fish. Easy-to-process plants like cactus pads were also eaten, but small seeds do not seem to have been an important part of Great Basin human diets until long after the Younger Dryas, closer to 9500 cal BP. The Great Basin record contains no evidence for natural catastrophe at the onset of the chronozone. Instead, the Younger Dryas appears to have been among the best of times for human foragers in this region of North America.     

Geoarchaeology of stratified paleoindian deposits at the Big Eddy site,Southwest Missouri,U.S.A.

The Big Eddy site (23CE426) in the Sac River valley of southwest Missouri is a rare recorded example of distinctly stratified Early through Late Paleoindian cultural deposits. Early point types recovered from the site include Gainey, Sedgwick, Dalton (fluted and unfluted), San Patrice, Wilson, and Packard. The Paleoindian record at Big Eddy represents only a fraction of the site's prehistoric cultural record; stratified cultural deposits in alluvium above the Paleoindian components span the entire known prehistoric sequence, and terminal Pleistocene alluvium may contain pre‐Early Paleoindian cultural deposits. This study focused on the paleogeomorphic setting, stratigraphy, depositional environments, pedology, geochronology, and history of landscape evolution of the late Pleistocene and early Holocene alluvium at the site. The Paleoindian sequence is associated with a complex buried soil 2.85 m below the modern surface (T1a) of the first terrace of the Sac River valley in the site vicinity. This soil formed at the top of the early submember of the Rodgers Shelter Member (underlying the T1c paleogeomorphic surface) and contains at least 70 cm of stratified Paleoindian cultural deposits, all in floodplain and upper point‐bar facies. A suite of 36 radiocarbon ages indicates that the alluvium hosting the Paleoindian sequence aggraded between ca. 13,250 and 11,870 cal yr B.P. (11,380 and 10,180 14C yr B.P.). Underlying deposits accumulated between ca. 15,300 and 13,250 cal yr B.P. (12,950 and 11,380 14C yr B.P.). By ca. 11,250 cal yr B.P. (9,840 14C yr B.P.) the T1c paleogeomorphic surface was buried by the earliest increment of a thick sequence of overbank sheetflood facies, ultimately resulting in deep burial and preservation of the Paleoindian record. The landform‐sediment assemblage that hosts the Paleoindian and possibly earlier cultural deposits at Big Eddy is both widespread and well preserved in the lower Sac River valley. Moreover, the terminal Pleistocene and early Holocene depositional environments were favorable for the preservation of the archaeological record. © 2007 Wiley Periodicals, Inc.     

Biodiversity,taxonomic richness and specialists-generalists during Late Pleistocene/Early Holocene times in Pampa and Patagonia (Argentina,Southern South America)

Human subsistence systems in the Pampa and Patagonia regions evolved from generalists during the Late Pleistocene/Early Holocene to specialists during the Middle Holocene, according to diversity and relative taxonomic richness counts. The general hypothesis is summarized as follows: 1) at the end of the Pleistocene and beginning of the Holocene (interval between 13.0 and 8.5 ka), the Pampean and Patagonian landscape was different from the present one, with a mammal biodiversity larger than in the Middle Holocene; 2) during the Middle Holocene, the highest mammal taxonomic richness corresponds to one species, Lama guanicoe. Although available biomass was the same for the hunter-gatherers, it was due to the larger abundance of individuals of that single species; 3) the emerged continental surface during the Late Pleistocene/Early Holocene was more extensive than during the Middle Holocene. In ecological terms, this greater land mass is reflected in an equally larger biodiversity, even assuming that populations of Pleistocenic megafauna were diminishing in number since ca. 13,500 years BP.Based on the analysis of our own information and published data, we state that the human groups which colonized the Pampean and Patagonian regions towards the end of the Pleistocene and beginning of the Holocene used generalist strategies encompassing a wide range of faunal resources (birds and mammals, especially of terrestrial habitats). Plasticity of hunter-gatherer societies, plus a complex technology, a higher social mobility and unfilled territories, allowed them to rapidly replace one resource for another in conditions of environmental stress. This lifestyle resulted in the occupation of different ecological zones (niches) and the evolution to specialized systems, based on one or a few mammal species, once the colonization and support in the different environments were successful and the resources of the Late Pleistocene/Early Holocene disappeared.     

Human choices and environmental constraints: deciphering the variability of large game procurement from Mousterian to Aurignacian times (MIS 5-3) in southwestern France

The evolution in the selection of prey made by past humans, especially the Neandertals and the first anatomically modern humans, has been widely debated. Between Marine Isotope Stages (MIS) 5 and 3, the accuracy of absolute dating is still insufficient to precisely correlate paleoclimatic and archaeological data. It is often difficult, therefore, to estimate to what extent changes in species procurement are correlated with either climate fluctuations or deliberate cultural choices in terms of subsistence behavior. Here, the full development of archeostratigraphy and Bayesian statistical analysis of absolute dates allows the archeological and paleoclimatic chronologies to be compared. The variability in hunted fauna is investigated using multivariate statistical analysis of quantitative faunal lists of 148 assemblages from 39 archeological sequences from MIS 5 through MIS 3. Despite significant intra-technocomplex variability, it is possible to identify major shifts in the human diet during these stages. The integration of archeological data, paleoclimatic proxies and the ecological characteristics of the different species of prey shows that the shifts in large game hunting can be explained by an adaptation of the human groups to climatic fluctuations. However, even if Middle and Early Upper Paleolithic men adapted to changes in their environment and to contrasting landscapes, they ultimately belonged to the ecosystems of the past and were limited by environmental constraints.     

东亚与北美细石叶遗存的古环境

对东亚和北美更新世晚期和全新世早期古环境的分析可以了解,细石叶遗存是一类分布于差异极大的生态环境中的器物。它们于东亚和北美的广布应与史前人类开拓动物资源为主和流动性很大的生存方式有关。它们之间的相似性很可能是由于传播和迁移而非多次的独立发明。     

How Bedrock‐Controlled Channel Migration Can Structure Selective Preservation of Archaeological Sites: Implications for Modeling Paleoindian Settlement

Although Paleoindian sites in Indiana, USA, are commonly located on late Wisconsin (Last Glacial Maximum) outwash terraces, drainage basin development since deglaciation often obscures the visibility of such sites on flood plains by either burying them under alluvium or destroying them through erosion. Significant clusters of Paleoindian and Early Archaic sites, however, have been identified proximal to the modern White River channel in central Indiana on what is mapped as “floodplain.” These site cluster locations are patterned. They typically occur within bedrock‐controlled river reaches but are rare along unconfined meandering reaches. Subsurface reconnaissance and chronology indicate that despite the fact that they often flood, portions of the so‐called flood plains within bedrock‐confined reaches are actually terraces constructed of late Wisconsin outwash with minimal overbank sedimentation. Terrace preservation in these settings is a result of bedrock structure that protects older sediments from lateral erosion and differentially preserves archaeological sites near the modern channel in bedrock‐controlled reaches. Comparisons of archaeological sites within bedrock‐controlled segments of the White River to those in unconfined meandering segments suggests that significant numbers of Paleoindian and Early Archaic sites may be missing from river settings across the midcontinent. These findings demonstrate that bedrock channel controls are important to recognize when assessing prehistoric settlement distributions.     

Paleoecological perspectives on human adaptation in central Panama. I. The Pleistocene

Paleoecological data from two sites in central Pacific Panama have allowed the reconstruction of Late Pleistocene climate and vegetation in lowland areas, the timing of important environmental changes, and the generation of predictions concerning Paleoindian settlement and subsistence. The last 9000 years of the glacial period, from 20,000 B.P. until 11,050 B.P. were marked by climates cooler and drier than today's. The period from ca. 16,000 B.P. until 11,000 B.P. appears to have been the coolest and driest. We postulate that the major effects of these conditions were to have brought montane vegetation 900 m lower than its present range and to create tracts of open landscape along the Pacific coast. Forests, however, were widespread in extent and many lowland forest taxa apparently persisted, creating the basis for the rejection of refugial theory as an explanatory model for early human occupation. Neither the admittedly limited archaeological or paleoecological data indicated the presence of pre-Clovis populations in Panama, and we chose to view Clovis as the first human expression on the Isthmus. Correlation of reconstructed environmental setting with Paleoindian site location suggests that Clovis adaptations were fluid and flexible, and utilized a wide variety of vegetation types. Occupation and modification of tropical forest appear to have been integral parts of Clovis subsistence and settlement strategies.     

Late Pleistocene and Early Holocene lake‐level fluctuations in the Lahontan Basin,Nevada: Implications for the distribution of archaeological sites

The Great Basin of the western U.S. contains a rich record of Late Pleistocene and Holocene lake‐level fluctuations as well as an extensive record of human occupation during the same time frame. We compare spatial‐temporal relationships between these records in the Lahontan basin to consider whether lake‐level fluctuations across the Pleistocene‐Holocene transition controlled distribution of archaeological sites. We use the reasonably well‐dated archaeological record from caves and rockshelters as well as results from new pedestrian surveys to investigate this problem. Although lake levels probably reached maximum elevations of about 1230–1235 m in the different subbasins of Lahontan during the Younger Dryas (YD) period, the duration that the lakes occupied the highest levels was brief. Paleoindian and Early Archaic archaeological sites are concentrated on somewhat lower and slightly younger shorelines (_1220–1225 m) that also date from the Younger Dryas period. This study suggests that Paleoindians often concentrated their activities adjacent to large lakes and wetland resources soon after they first entered the Great Basin. © 2008 Wiley Periodicals, Inc.     

Sedimentological and palaeoenvironmental study from Waregi Hill in the Hiwegi Formation (early Miocene) on Rusinga Island,Lake Victoria,Kenya

Palaeontological deposits on Rusinga Island, Lake Victoria, Kenya, provide a rich record of floral and faunal evolution in the early Neogene of East Africa. Yet, despite a wealth of available fossil material, previous palaeoenvironmental reconstructions from Rusinga have resulted in widely divergent results, ranging from closed forest to open woodland environments. Presented here is a detailed study of the sedimentology and fauna of the early Miocene Hiwegi Formation at Waregi Hill on Rusinga Island, Kenya. New sedimentological analyses demonstrate that the Hiwegi Formation records an environmental transition from the bottom to the top of the formation. Lower in the Hiwegi Formation, satin-spar calcite after gypsum in siltstone deposits are interpreted as evidence for open hypersaline lakes. Moving up-section, carbonate deposits – interpreted previously as evidence of aridity – are actually diagenetic calcite cements, which preserve root systems of trees, suggesting a more closed environment; further up-section, the uppermost palaeosol layer contains abundant root traces and tree-stump casts, previously reported as evidence of a closed-canopy forest. These newly interpreted environmental differences are reflected by differences in faunal composition and abundance data from Hiwegi Formation fossil sites R1 and R3. Taken together, this work suggests that divergent palaeoenvironmental reconstructions in previous studies may have been informed by time-averaging across multiple environments. Further, results demonstrate that during the early Miocene local or regional habitat heterogeneity already existed. Rusinga’s Hiwegi Formation varied both spatially and temporally, which challenges the interpretation that a broad forested environment stretched across the African continent during the early Neogene, transitioning later to predominately open landscapes that characterize the region today. This result has important implications for interpretations of the selective pressures faced by early Miocene fauna, including Rusinga Island’s well-preserved fossil primates.     

中国新近纪哺乳动物群的演化与青藏高原隆升的关系

新近纪哺乳动物的起源、辐射、扩散、绝灭等方面反映了气候环境的重大变化,晚新生代青藏高原的形成对东亚地区哺乳动物的演化具有直接而深远的影响。高原的隆升使自然环境发生改变,环境的变化又导致动物组成和分布的分异,以及动物对环境适应性的调整。中国新近纪哺乳动物化石研究的结果不仅表明哺乳动物群的组成和特征具有明显的区域性差异,而且中国还是一些代表性门类的起源扩散中心,也是哺乳动物洲际迁徙的关键通道。青藏高原新近纪晚期的哺乳动物群具有非常重要的意义,因为在随之而来的第四纪冰期中这些寒冷适应性动物获得了优势地位,由此成为现代动物地理区系和多样性的基础。通过以点带面的综合研究,将能够全面地认识新近纪动物地理区系对重大气候事件的响应,更准确地判断青藏高原隆升对陆地生态系统的影响。     

Investigating human and megafauna co-occurrence in Australian prehistory: Mode and causality in fossil accumulations at Cuddie Springs

Human arrival in Sahul – Pleistocene Australia and New Guinea – has long been argued as the catalyst in the decline and disappearance of a suite of extinct animals referred to as megafauna. The debate concerning causality in Sahul is highly polarised, with climate change often cited as the alternative explanatory model. On continental Australia, there are few datasets available with which to explore the likely processes leading to the extinction events. At the present time, there is one site in New Guinea (Nombe Rockshelter) and one on continental Australia (Cuddie Springs) where the coexistence and temporal overlap of humans and megafauna has been identified. The Cuddie Springs Pleistocene archaeological site in southeastern Australia contains an association of fossil extinct and extant fauna with an archaeological record through two sequential stratigraphic units dating from c. 36 to c. 30 ka ago. A taphonomic study of the fossil fauna has revealed an accumulation of bone in a primary depositional context, consistent with a waterhole death assemblage. Overall the faunal assemblage studied here (n: 8146; NISP: 1355) has yielded little direct evidence of carnivore damage or human activities. Post depositional factors such as physical destruction incurred by trampling, compaction of sediments, and/or the hydrological status of the lake at that time have played important roles. As the only known site on continental Australia where megafauna and humans co-occur, the Cuddie Springs faunal assemblage yields equivocal evidence for a significant human role in the accumulation of the fauna here. At the present time there is no evidential basis to the argument that humans had a primary role in the extinction of the Australian megafauna. The first colonisers are likely to have preyed upon those few species known to have persisted to this time, but their impact may have been restricted to the tail end of a process that had been underway for millennia prior to human arrival.     

Terminal Pleistocene/Early Holocene Environmental Change at the Sunshine Locality, North-Central Nevada, U.S.A.

Sedimentological, faunal, and archaeological investigations at the Sunshine Locality, Long Valley, Nevada reveal a history of human adaptation and environmental change at the last glacial–interglacial transition in North America's north-central Great Basin. The locality contains a suite of lacustrine, alluvial, and eolian deposits associated with fluvially reworked faunal remains and Paleoindian artifacts. Radiocarbon-dated stratigraphy indicates a history of receding pluvial lake levels followed by alluvial downcutting and subsequent valley filling with marsh-like conditions at the end of the Pleistocene. A period of alluvial deposition and shallow water tables (9,800 to 11,000 ¹⁴C yr B.P.) correlates to the Younger Dryas. Subsequent drier conditions and reduced surface runoff mark the early Holocene; sand dunes replace wetlands by 8,000 ¹⁴C yr B.P. The stratigraphy at Sunshine is similar to sites located 400 km south and supports regional climatic synchroneity in the central and southern Great Basin during the terminal Pleistocene/early Holocene. Given regional climate change and recurrent geomorphic settings comparable to Sunshine, we believe that there is a high potential for buried Paleoindian features in primary association with extinct fauna elsewhere in the region yet to be discovered due to limited stratigraphic exposure and consequent low visibility.     

Lubbock Lake: Late Quaternary cultural and environmental change on the Southern High Plains,USA

Lubbock Lake (Southern High Plains of Texas) contains a cultural, faunal, and floral record within a virtually complete geological record spanning the past 11 100+ years. More than 88 archaeological occurrences have been excavated from five major stratigraphic units. The Paleoindian record (11 500–6500yr BP) begins with Clovis-age occupation (ca. 11 100yr BP) found within fluvial deposits (stratum 1). Subsequent Paleoindian occupations are found in lake and marsh sediments (stratum 2). Archaic occupations (8500-2000yr BP) are contained within aeolian and marsh deposits (strata 3 and 4). Ceramic occupations (2000-500yr BP) are found on a soil developed in stratum 4, in marsh sediments (strata 4 and 5), and in slopewash and aeolian sediments (stratum 5). The Protohistoric (500-300yr BP) and Historic (300-100yr BP) remains are in slopewash, aeolian, and marsh sediments (stratum 5) and associated soils. The Southern High Plains remained a grasslands throughout the last 11 500 years and neither man nor bison abandoned the region. The successive local faunas reflect changing ecosystems under pluvial to arid to more mesic to semiarid conditions. The occupation of Lubbock Lake through time appears to have been by small groups of people for both economic and short-term residential uses. These hunter-gatherer peoples underwent adaptive change brought about by climatic stress and alterations to food resources.     

Generalism as a subsistence strategy: advantages and limitations of the highly flexible feeding traits of Pleistocene Stephanorhinus hundsheimensis (Rhinocerotidae,Mammalia)

The so-called Hundsheim rhinoceros, Stephanorhinus hundsheimensis, was a very common faunal element of the Early to early Middle Pleistocene period in the western Palaearctic. In this study, individuals from two different central European populations of the Hundsheim rhinoceros were analysed in order to determine whether their local dietary signals could reflect differing food availability between the two populations, and whether such information could provide a better understanding of the ecological role of S. hundsheimensis within corresponding faunal assemblages, and of its principal subsistence strategy in the western Palaearctic. The mesowear traits observed in the studied S. hundsheimensis populations have been interpreted as representing biome-specific signals, indicating grassland vegetation at the site of Süßenborn, and dense to open forests at Voigtstedt (both localities in Germany). The analyses performed on the fossil rhino material demonstrate the most pronounced dietary variability ever established for a single herbivorous ungulate species by mesowear studies. This variability ranges from an attrition dominated grazing regime, to a one of predominantly browsing, and characterises S. hundsheimensis as the most ecologically tolerant rhinoceros of the Palaearctic Plio-Pleistocene. Although such dietary flexibility proved an effective enough subsistence strategy over a period of 600–900 ka (1.4/1.2–0.6/0.5 Myr) in the western Palaearctic, the situation changed dramatically after 0.6 Myr BP, when the new species of rhinoceroses, Stephanorhinus hemitoechus and Stephanorhinus kirchbergensis, appeared and started to compete for both the grass and the browse. For the generalist S. hundsheimensis, this bilateral interference was detrimental to its success in all of its habitats. The successful competition of specialised forms of rhinoceroses, which might have originated as a result of the development of 100 ka periodicity in the global climatic record, is proposed as the main reason for the extinction of S. hundsheimensis during the early Middle Pleistocene.     

北祁连造山带中—西段陆壳残块群的构造—地层特征

北祁连造山带是一条多旋回的造山带,其最大特点是早古生代岩系中镶嵌有众多大小不一的由前震旦系变质岩系所组成的陆壳残块群,它们源于晋宁期末,统一的巨型华北古大陆早古生代初的裂解。寒武 奥陶纪西段演化为裂谷系,陆壳残块群组成裂谷系的正性隆起构造单元;中段发育微洋盆沟弧盆体系,在南缘的陆壳残块群处于奥陶纪活动大陆边缘张裂带上,并构成被晚期弧后盆地及裂谷分开后的陆壳基底部位,少数陆壳残块为沟弧盆体系中的孤岛隆起。它们不是由中祁连推覆来的飞来峰或是外来移置的滑覆体,而是由统一的巨型华北古大陆西南缘古阿拉善地块于早古生代初裂解后向洋或裂谷演化过程中残留其中的大小不一的陆壳残块。北祁连早奥陶世海域与现在加拿大北部巴芬湾及伊丽莎白女王群岛的构造格局相似。     

A geoarchaeological approach to using surface sites for paleoenvironmental reconstructions

Archaeological sites that have only surface scatters are usually considered to be of little or no use in reconstructing paleoenvironmental conditions during episodes of human occupation. However, geoarchaeological research at the Skare site in south-central Wisconsin reveals that these sites can be used to provide information about the timing of paleoenvironmental changes and their affect on the location of human occupations. Geomorphic investigations revealed the presence of Alfisols formed in late Wisconsin loess on upland and low bench positions; morphologically younger Mollisols formed in alluvial and colluvial sediments on low alluvial plain positions; and beach sediments that represent the low-water stand of Glacial Lake Yahara. Semiquantitative age control for timing the formation of these soils and the lake level(s) of Glacial Lake Yahara is based on the location of diagnostic artifacts (Early Paleoindian to Late Woodland) recovered during ten separate surface collections. Early and Late Paleoindian artifacts all occur on Alfisols and are only found above the low-water stand of Glacial Lake Yahara, indicating that loess deposition and subsequent soil formation happened sometime between 12,000 and 11,000 yr B.P., and that Glacial Lake Yahara remained near the low-water stand at least until ∼9500 yr B.P. Early Archaic artifacts are present below the low-water stand and provide ages for lowering of the lake to be between 8000 and 9500 yr B.P. Middle Archaic artifacts are present on Mollisols and provide an age of soil formation to be between 5000 and 3000 yr B.P. A majority of Woodland artifacts occur on these Mollisols and are present along the floodplain of the Yahara River, possibly representing a change in subsistence strategy and settlement patterns relative to Paleoindian and Archaic occupations. The agreement of soil morphological and sedimentological data with semiquantitative age data of diagnostic artifacts provides evidence that archaeological surface scatters can be useful tools in dating soils and landforms associated with these sites. © 1998 John Wiley & Sons, Inc.     

A “marginality” model to explain major spatial and temporal gaps in the old and new world Pleistocene settlement records

A key argument currently invoked to cast skepticism on certain South American sites, that suggest a first peopling of the New World by ca. 35,000 B.P., is the perplexingly low visibility of the archaeological record until 12,000 B.P. But, contrary to a popular misconception, great spatial and temporal discontinuities are common in the Old World Paleolithic settlement record. In Southern Africa, carefully controlled archaeological stratigraphies show that the now semiarid interior was unoccupied for 50,000 and more years at a time. Episodes of widespread settlement in marginal environments were relatively brief, limited to periods of substantially wetter climate, and closely linked with moist habitats. A risk-minimization model is proposed to explain these discontinuities. Plant and animal resources in the region, given a climate as dry or drier than today, were of low productivity and low reliability for unspecialized hunter-gatherers during the dry seasons of poor years. This would require large foraging territories and very wide spacing of proximal bands, so that the exchange of vital information on temporary or migratory resources was minimal. Finally, during extended droughts, fat-depleted animals provided an unsatisfactory source of food. These variables suggest that environments with low productivity and predictability were too risky for unspecialized hunter-gatherers with a pre-Upper Paleolithic technology, such as those who would have been able to enter the New World 35,000 B.P. Major spatial and temporal gaps in the New World settlement record should therefore be expected prior to the appearance of specialized Paleoindian hunter-gatherers ca. 12,000 B.P. Implications for geoarchaeological strategies are discussed.     

The Ñuagapua alluvial fan sequence: Early and Late Holocene human-induced changes in the Bolivian Chaco?

The Quebrada Ñaguapua alluvial fan provides a record of changes that have affected the Bolivian Chaco during the Holocene. The 4th oldest Unit, possibly related to the last glaciation, is restricted to the fan apex; it was deeply dissected during the Early Holocene, with three other units emplaced within the resultant incision. Sandy sediments characterise Unit 1 and 3 while Unit 2 is a forest soil that marks a period of stability. The oldest Unit 1 was deposited just before 6900 years BP. It contains artefacts that represent the earliest evidence of human occupation and suggests that deposition was perhaps induced by deforestation. Anthropogenic deforestation is evident at the base of Unit 3, which contains a wooden plank (140 years BP), charcoal, ash and charred tree-trunks. Some trunks have been burnt in situ while others survived the fire and are still growing, although their roots emanate from Unit 2. Although, similar events slightly to the north have been attributed to climatic changes, the delay in soil erosion in closely spaced areas could be plausibly attributed to human-induced changes. Megafaunal remains in Unit 1 represent the last occurrence of megafauna, including horse, in South America. The faunal association is anomalous because of the concurrent presence of aquatic, forest and open-environment species. We suggest that the last migrated from the southern part of Continent, where ecologic conditions allowed their survival in the Early Holocene, after the widespread clearing of the natural forest and shortly prior to the extinction of the Magafauna.