Abstract Questions surrounding the chronology, place, and character of the initial human colonization of the Americas are a long-standing focus of debate. Interdisciplinary debate continues over the timing of entry, the rapidity and direction of dispersion, the variety of human responses to diverse habitats, the criteria for evaluating the validity of early sites, and the differences and similarities between colonization in North and South America. Despite recent advances in our understanding of these issues, archaeology still faces challenges in defining interdisciplinary research problems, assessing the reliability of the data, and applying new interpretative models. As the debates and challenges continue, new studies take place and previous research reexamined. Here we discuss recent exploratory excavation at and interdisciplinary data from the Monte Verde area in Chile to further our understanding of the first peopling of the Americas. New evidence of stone artifacts, faunal remains, and burned areas suggests discrete horizons of ephemeral human activity in a sandur plain setting radiocarbon and luminescence dated between at least ~18,500 and 14,500 cal BP. Based on multiple lines of evidence, including sedimentary proxies and artifact analysis, we present the probable anthropogenic origins and wider implications of this evidence. In a non-glacial cold climate environment of the south-central Andes, which is challenging for human occupation and for the preservation of hunter-gatherer sites, these horizons provide insight into an earlier context of late Pleistocene human behavior in northern Patagonia.

Citation: Dillehay TD, Ocampo C, Saavedra J, Sawakuchi AO, Vega RM, Pino M, et al. (2015) New Archaeological Evidence for an Early Human Presence at Monte Verde, Chile. PLoS ONE 10(11): e0141923. https://doi.org/10.1371/journal.pone.0141923 Editor: John P. Hart, New York State Museum, UNITED STATES Received: April 28, 2015; Accepted: October 14, 2015; Published: November 18, 2015 Copyright: © 2015 Dillehay et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited Data Availability: All relevant data are presented within the paper and its Supporting Information files. Funding: This research was funded by the National Council of Monuments, Chile, the National Geographic Society, Vanderbilt University, SERNAGEOMIN, Chile, Instituto de Geociencias, Universidad Austral de Chile, Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Instituto de Geociências, Universidade de São Paulo, Brasil. The funding organizations had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. The funders provided support in the form of only travel, salary, field and laboratory costs for some authors [MP, CO, JS, RV, LSC], but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section. The Paleo Research Institute provided analytical services for only the pollen and phytolith studies. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: The commercial affiliation with the Paleo Research Institute does not alter the authors' adherence to PLOS ONE policies on sharing data and materials.

Discussion Paleovegetation records in the study area suggest that climate warming occurred between ~26,000 and 18,400 cal BP, with short cooling events at ~25,100 and 18,100 cal BP. Warming after the last glacial termination was well underway by ~17,600 cal BP and was followed by warmer pulses at ~17,000 and 15,300 cal BP. Post-glacial conditions changed to a cool, temperate climate by ~15,000 cal BP, slightly cooler and wetter than today [31–33,48], a time when the Chinchihuapi Creek formed. These intermittent warming trends correspond with most of the archaeological horizons recorded in sites MV-I, CH-1 and CH-II between ~18,500 and 15,000 cal BP and with the later, more prolonged presence of people at MV-II around ~14,500 cal BP. During all periods, volcanic eruptions and ecological barriers may have impacted people’s movements, as suggested by the numerous tephra lenses at sites and especially by a coating of ash on the artifacts at MV-II [14,34]. The new horizons represent low-density, discontinuous cultural deposits that contain few cultural materials. This suggests discrete, functionally similar, short-term anthropogenic activities most likely associated with hunting and gathering, heating food in small hearths, and producing and discarding expedient stone tools. More than a third of the stone tools associated with these deposits are made of exotic material, suggesting a high degree of mobility and/or long-distance exchange. If these scenarios are correct, then the settlement pattern in the Monte Verde area during this period was probably just one of several with small groups of people seasonally adapted to cold parkland and boreal environments, most likely during the warmer months. After ~17,000 cal BP, when the environment changed to a slightly warmer Northern Patagonian forest and after 15,000 cal BP, when the Chinchihuapi Creek formed, people settled for a longer stay as evidenced by more varied resources and artifact types and by the more extensive cultural deposits at MV-II. We had postulated previously that the wide variety of local and non-local resources at MV-II [13,14,25], which were obtained from a mosaic of environmental zones extending from the western Argentina steppes to the Pacific coastline, suggests direct procurement by people at the site. Given the detailed knowledge required to exploit several highly specific species (including medicinal plants and seaweeds) from different and distant zones, we now consider an additional explanation to account for the presence of exotics at the site, that is, exchange with different groups of people dispersed across these zones. It does not seem feasible that people at MV-II would have had intimate knowledge of so many different resources spread over such a large area. This knowledge was most likely learned and shared by several groups actively involved in exchange networks by at least 14,500 cal BP. Lastly, because few historical and present-day foragers have been documented in similar types of cold, post-glacial environments, it is difficult to use ethnographic analogy to gain insight into the possible types of archaeological records and inferred human behaviors we might expect for this earlier time period in south-central Chile. Perhaps one of the closest analogues is the Nunamiut of northern Alaska who made sporadic and brief hunting trips into cold, post-glacial-like environments, creating an ephemeral material record of small scattered hearths, bone remains, and other traces [49]. In comparison, there are several archaeological studies in periglacial and glaciogenic settings in high northern latitudes that discuss early pebble tool cultures and ephemeral, discontinuous archaeological records [50,51], which seem to be similar in some ways to the data presented here.

Conclusion An element that seems predictable in the archaeological horizons reported here is that the successive human presence in the Monte Verde area between at least 18,500 and 14,500 cal BP is likely to have been connected to Pacific coastal locations and possibly to deglaciated passes through the Andes to the Argentine steppes. This is suggested by the presence of exotic raw lithic materials dated to this period and plant species from both areas, especially those from coastal beaches and estuaries at MV-II [14,25]. It is doubtful whether local inhabitants would have procured non-local lithics when suitable basalts, andesites, quartzites, and other stones were readily available in the site area. The presence of a relatively high number of these materials prior to ~14,500 cal BP most likely suggests people from distant areas passing through the Monte Verde area. In turning to a methodological issue, the new archaeological horizons in the Monte Verde area are difficult to trace laterally over areas larger than ~8–10 m2 and probably represent only fragments of a broader landscape utilized by people adapting to changing climates and environments in the area. More of these horizons surely exist in the site areas at different vertical and horizontal locations undiscovered by out recent investigation. If we had employed a different excavation strategy focused more on extended, large block excavations than on discontinuous, systematically-placed cores, test pits and limited block excavations, we probably would have obtained similar results. That is, more extensive horizon excavation also probably would have revealed the same discontinuous and ephemeral nature of the earlier archaeological record of MV-I and CH-I and CH-II sites, which we first documented in the early 1980s (13,14). The criteria for defining and explaining some early sites may gradually change as we reconsider the scale of analysis applied by current research designs. For instance, when we first excavated the MV-II site in the late 1970s, we opened spatially limited areas (5 by 8 m and a few outlying 1 by 2 m test pits). These areas exposed one bifacial tool, a few unifacial flakes, and the bone remains of “mastodonts” or gomphotheres [24,47]. Later in the 1980s, when we returned to the site and excavated three larger excavation blocks (~6 by 15 m and more test pits and trenches), we discovered the dense and more extensive structured evidence of the MV-II occupation [13,14]. Now, after the recent investigation of a more extensive area and of other types of depositional environments in the site, we have discovered a different, more complex ecological and ephemeral archaeological setting. Would the type of evidence at and our thinking of previously some excavated early sites in other areas of the Americas change if they were reexamined and more extensively excavated? Furthermore, the type of ephemeral records revealed at sites like MV-I and CH-I does not easily fit the criteria of more laterally and/or vertically dense cultural deposits evidenced at later sites, such as MV-II, Arroyo Seco in Argentina [52], Gault and Friedkin sites in Texas [9–10], Clovis and other early localities in North America [1,8,11]. These and especially the later Clovis and Fishtail sites may represent a time when landscape use had risen to the point of being more archaeologically visible as a result of human populations exploratory less and colonizing and settling in more. The discontinuous and minimal nature of earlier records and particularly those reported in Brazil [12,15,16, 22,23,28,53], Peru [45] and North America [8–9] challenge us to consider a wider variety of temporal, spatial and archaeological scales of early, possibly first arrival, human activity associated with sites of low archaeological visibility and with stone and bone technologies sometimes different from what we expect. The types of discontinuous and short-lived records reported here make the task of defining their archaeological and taphonomic characteristics and evaluating their scientific validity or invalidity more difficult than expected. To conclude, the chronology and nature of the peopling of the New World are the focus of great deliberation between multiple schools of thought: some stress a short chronology and others a long chronology, some advocate one migration and others multiple migrations, some point to Asia as the only source of human entry and others point to Europe. For the moment, the majority of anatomical, archaeological and genetic evidence gives credence to the view that people were relatively recent arrivals to the Americas, probably sometime between 20,000 and 15,000 years ago. The current evidence presented here for the Monte Verde area best fits this scenario; however, this may change as more data are gathered and assessed. The early archaeological record of the Americas continues to be remarkably unpredictable and intriguingly complex.

Supporting Information S1 Fig. View of present-day drainage setting with elevated areas and patchy vegetation. . This low-energy setting, situated near the modern-day glacial below the active volcano of Tronador located about 50 km east of Monte Verde, is topographically and ecologically reminiscent of the sandur plain at the site that was occupied in late Pleistocene times. Note the narrow and shallow trough drainages slightly eroded by seasonal rainwater and snowmelt and the intact, uneroded vegetated rises between them, the latter similar to those containing the archaeological horizons reported here in the buried sandur plain at Monte Verde. https://doi.org/10.1371/journal.pone.0141923.s001 (PDF) S2 Fig. Schematic profile of archaeological horizons and OSL dated samples in sites. a. Schematic profile of the location of archaeological horizons and OSL dated samples (Unit 45(A)) on uneroded, elevated areas between the narrow, shallow channels of the braided system in the buried sandur plain of the Monte Verde area; b-g. schematic profiles of the sedimentological and archaeological deposition phases for the study area; b. the two profiles, one from Unit 45(A) on the south side of the present-day Chinchihuapi Creek and the other from the MV-II site in the north bank terrace of the creek, correlate chronologically and sedimentologically. An OSL date reveals the MV-II occupation resting on the palimpsest surface of MV-7 stratum. Stratum MV-7 was deposited around 42,000 years ago and then exposed ~15,000 years ago when the creek formed (stratum MV-6 is the ancient creek bed). Around 15,000 years ago Chinchihuapi Creek downcut and washed away the upper and middle levels of stratum MV-7 in the north section (the ~40,000–14,000 year upper and middle layers of stratum MV-7 shown in section D of the profile of Unit 45(A) were not eroded). While the ~42,000 year surface was exposed ~15,000 years ago in the north section, the MV-II occupation took place shortly afterwards ~14,500 years ago and then sometime before 14,000 years ago both the exposed ~42,000 year surface of stratum MV-7 and the MV-II archaeological remains resting on it in the north section were buried by the subsequent deposition of strata MV-1 to MV-5. As indicated by the new evidence reported here, the uneroded surface and upper level of stratum MV-7 on the higher south side (Unit 45(A)) of the creek also were occupied between ~14,500 and 14,000 years ago; c-g. depositional and erosional Phases I-V schematically represent the sedimentological and archaeological sequence across site areas: c. Phase I: beginning before ~45,000 years ago the high terrace in site MV-I (Unit 45 (A)) was formed and comprised of intermittent shallow channels making up the braided stream system of the sandur plain. The channels roughly flowed from southeast to northwest; d. Phase II: after ~33,000 years ago the upper and middle levels of stratum MV-7, the high terrace levels as depicted in Unit 45 (A), were eroded in some places (curvy yellow line), then between 28,000 and 15,000 years ago new deposits of shallow braided stream channels were formed, including the airborne deposition of tephra lenses and the subsequent intermittent seasonal occupations by humans between 19,000 and 15,000 years ago. Sediment deposition during this phase was not continuous as indicated by non-depositional hiatuses; e. Phase III: ~15,000 years ago, deep lineal erosion occurred in some places and the Chinchihuapi Creek was formed (the date for the upper level of stratum MV-6, the creek bed, is shown in b,f and g), washing away the upper and middle levels of stratum MV-7 in the north section and exposing the surface of the ~42,223 year level of this stratum, upon which the MV-II occupation took place: f. Phase IV: a soil contemporary with the deposition of stratum MV-4 developed in the area of Unit 45(A) in the south section and strata MV-4 and MV-5 formed over and sealed the MV-II site in the north section; g. Phase V, strata MV-1 to MV-3 formed in both sections. https://doi.org/10.1371/journal.pone.0141923.s002 (PDF) S3 Fig. Thin tephra lenses in the past and present. a: arrows point to one of several thin, orange pumice lapilli lenses typical of those found throughout the MV-7 stratum containing the archaeological horizons; b: ventral side of a percussion flaked tool embedded in a 2 cm thick tephra lens located on an uneroded, elevated surface between narrow drainage channels in stratum MV-7, Unit 56 (see Fig 6b for a close-up of the dorsal side of the flake); c: typical micro-setting where thin orange lenses form during the summer months in shallow humid grassy areas at Monte Verde. https://doi.org/10.1371/journal.pone.0141923.s003 (PDF) S4 Fig. Archaeological features showing underlying tephra lens and burned area. a. Oval-shaped object of clay associated with a percussion struck lithic in Unit 55; b. Feature 9 in Unit 45(A) showing underlying orange tephra lens and overlying burned area with in situ patch of charcoal (bottom arrow) and percussion flake (top arrow). https://doi.org/10.1371/journal.pone.0141923.s004 (PDF) S5 Fig. Epiphysis of animal tibia. Fractured and partially burned epiphysis of a tibia probably of a deer or horse from Unit 56, MV-I dated at 13,940–13,560 cal BP (see Table 1). https://doi.org/10.1371/journal.pone.0141923.s005 (PDF) S1 File. Text A. Description of Lithics. Text B. Chrono-Stratigraphy of the 2013 Cultural Materials. Text C. Mineral, Petrographic and SEM Analyses of Tephra Sediments. Text D. Micromorphological Analysis of Archaeological Sediments. Text E. Magnetic Analysis of Archaeological Sediments. Text F. Pollen, Phytolith, and Starch Grain Analyses of Features. Text G. Optimal Luminescence Dating. Text H. Lithic Micro-Usewear Study. https://doi.org/10.1371/journal.pone.0141923.s006 (DOCX)

Acknowledgments We thank all of the local Monte Verdinos who helped us during the field season as well as the following individuals: K. Barrientos, T. Cárdenas, F. Delgado, K. Duguet, C. Ilabaca, P. Jara, M. Jiménez, R.A. Varney, D. Millafilo, N. Oliva, B. Pinto, M. Reyes, and M. Toro. Iris Bracamonte did the lithic drawings. Much gratitude is also extended to Eduardo Alvar of the Fundacion Monte Verde for his administrative aid and logistical support. We thank Ignacio Kuschel for giving us permission to excavate on a portion of his land. Lastly, we appreciate the comments of anonymous reviewers.

Author Contributions Conceived and designed the experiments: TD CO JS RV MP MC LSC AS MM XV GH GD. Performed the experiments: TD CO JS RV MP MC LSC AS MM XV GH GD IA AG. Analyzed the data: TD CO JS RV MP MC LSC AS MM XV GH GD. Contributed reagents/materials/analysis tools: TD RV MP LSC MM XV GH GD. Wrote the paper: TD RV MP MC LSC MM XV GH GD.