In light of the concerns raised about the accuracy of the data and the strength of support for the original conclusions, the PLOS ONE Editors retract this article.

The PLOS ONE Editors have considered the amendments to the data and have consulted with an external peer reviewer and a member of the Editorial Board. Following evaluation, there are concerns about the reliability of the results and conclusions, and some results are no longer supported, as follows:

Following publication, the author informed the journal office that there are errors in the data reported in the article [ 1 ]. Specifically, the compass measurements used in Figs 9, 11, 12, and 13 are inaccurate due to magnetic distortion in the study area. When the compass measurements are corrected, the following results are no longer supported:

Abstract The archaeological sites near Monte Alegre, along Brazil's lower Amazon River, provide new information on the little-known activities and symbolism of South American Paleoindians toward the end of the Ice Age. While paleoindian sites like Monte Verde in Chile, or Guitarrero Cave in Peru, are located near the pacific coast, Monte Alegre lies much further inland, 680 km upriver from the mouth of the Amazon River and the Atlantic Coast. With excavated wood charcoal radiocarbon dated as early as 13,200 calibrated years ago, the hill—as a source of sandstone and quartz lithics—supplied early pioneers with adequate tools needed for colonizing the interior of the continent. Once there, they painted rock art on the landscape, which bears a record of the sun's horizon positions throughout the year. At just 2° south of the equator, Monte Alegre shows no overt seasonal changes beyond fluctuating rainfall amounts, unlike at higher latitudes where temperature, amount of daylight, foliage, and forms of precipitation markedly change. Near the equator, solar and stellar horizon sightings most visibly track the passage of time and seasonal cycles. However, horizons are often hidden behind high forest canopy throughout much of the Amazon Rainforest; but in the Monte Alegre hill ridges looming above the river, paleoindians could hike above the canopy to peer at the horizon, more effectively synchronizing their activities to ecological cycles. This research suggests that Monte Alegre paleoindians delimited the azimuthal range of the sun in a solar year with notational pictographs aligned to horizon sightings at Painel do Pilão, and leaving a painted grid of tally marks that might have served as a rudimentary early calendar. The broad-reaching implication for early Americans is that through the strategic placement of rock art, these ancient artists fostered predictive archaeorecording from which resources could be optimally extracted, ceremonial activities could be consistently scheduled, and gatherings for social and economic exchange could be more efficiently coordinated.

Citation: Davis CS (2016) Solar-Aligned Pictographs at the Paleoindian Site of Painel do Pilão along the Lower Amazon River at Monte Alegre, Brazil. PLoS ONE 11(12): e0167692. https://doi.org/10.1371/journal.pone.0167692 Editor: Roberto Macchiarelli, Université de Poitiers, FRANCE Received: October 17, 2016; Accepted: November 18, 2016; Published: December 20, 2016 Copyright: © 2016 Christopher Sean Davis. 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 within the paper and its Supporting Information files. Funding: U.S. Student Fulbright Commission with Fulbright Brasilia (www.fulbright.org.br) partially supported (cost of living and transportation, research permits) funding for the research of CSD. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. All remaining research was unfunded. Competing interests: The author has declared that no competing interests exist.

Introduction Approximately fifteen kilometers southwest of the city of Monte Alegre, in the Brazilian state of Pará, ancient rock art sites dot the caves and rock faces of three hilly sandstone ridges that are adjacent to the northern bank of the Amazon River [see 1]. Nearly all of the 600+ images are pictographs painted in red to yellow earth tones and unevenly distributed among fourteen different sites. Four of the fourteen sites are open-air vertical rock walls or outcrops while the remaining ten are in small caves or shallow rock shelters. All the outdoor sites contain individual pictographs as well as panels of grouped paintings. Most of the cave and shelter sites have individual pictographs, except for the outer entryway pictographs at Caverna da Pedra Pintada, which are clustered like panels. Anna Roosevelt and her team (1996) excavated at Caverna da Pedra Pintada, the largest and closest painted cave to the Amazon River, on a hill called Serra da Paituna. There they unearthed evidence of a Late Pleistocene paleoindian occupation period associated with numerous paint drops and lumps of pigment, artifacts, black soil, and other food remains radiocarbon dated to 11,280 to 10,170 uncalibrated years before present (13,630–11,705 cal yr BP—OxCal 4.2) [2–4]. This research corroborates Roosevelt's work by unearthing further evidence of a paleoindian rock painting tradition at Painel do Pilão, a nearby open-air outcrop approximately 400 meters from Caverna da Pedra Pintada. Evidence consists of an excavated ochre manuport and a buried painted stone among lithic flakes and boulders quarried from a sandstone schist wall, and deposited in the lowest stratigraphic levels of a small shelter. The wall from which rocks were removed serves as a platform for an observer to stand atop to view red and yellow painted pictographs, some of which depict probable sun and sky-themed representations due to their solstice alignments, and a grid pattern with filled-in tally marks. The solar alignment of these paintings, and the dated antiquity of contextual artifacts and features from the excavation, suggest a tradition of naked-eye ethnoastronomy and rock art took place here, and the grid may have served as one of the earliest solar "calendars" in the Americas.

Painel do Pilão Rock Shelter at Monte Alegre Monte Alegre is a town on the eastern edge of a geologic dome of Paleozoic bedrock, which is interrupted by Tertiary graben-like sediment in horizontal layers of schist, clayey schist, and very fine-grained quartzite, along with dyke intrusions of diorite. The dome partly redirects the Amazon River, which bends north around the dome's eastern edge, and floods into Lago Grande lake just south of the dome during the rainy season. This makes the Monte Alegre dome a rare location in the Lower Amazon Basin because the hill ridges appear like gently sloping rocky plateaus (Fig 1) from the river. PPT PowerPoint slide

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larger image TIFF original image Download: Fig 1. Serra do Ererê Hill as seen from the Amazon River in mid Spring. To ancient navigators on the Lower Amazon River, this hill would be a place to replenish silicified sandstone lithic tools. Photo taken by Chris Davis on May 2, 2011. https://doi.org/10.1371/journal.pone.0167692.g001 For a Paleoindian culture, the hills offered a lithic source for making sandstone, quartz, and chalcedony stone tools. Its microclimate zones would also have offered hunting grounds for diverse land and aquatic game, like turtle, brocket deer, and macaws; its seasonal marshes allowed for relative ease of mobility by canoe navigation; the caves offered shelter; and the peaks offered a vantage point above the rainforest canopy to monitor fluctuating river levels and make horizon sightings to coordinate seasonal subsistence strategies. The rock art and archaeological excavations appear to support this scenario of land use.

Methods The excavation At Painel do Pilão was carried out in late April and May of 2011 with the field permit granted by CNPQ and IPHAN- Belém, PA under the supervision of Dra. Denise Schaan at the institute: Universidade Federal do Pará, Belém, Brazil and Universidade Federal do Oeste do Pará, Santarém, Brazil". The entire width of the shelter floor, covering approximately 1.6 x 1.8 meters, was excavated to bedrock at a depth of ~2.6 meters by the author, who was assisted by two local residents, and a Brazilian archaeology student. Excavation levels were determined by natural levels evaluated from changes in sediment grain-size, sorting, and munsell soil colors. The total number of specimens excavated were 1,688 stored in a permanent repository at the Universidade Federal do Oeste de Pará in Santarém, Brazil. Photographs and Brunton compass readings of the pictographs were taken in 2007 and 2008, and additional photos and enhanced photogrammetric techniques were taken in 2010 using a handheld GPS unit and a gigapan panoramic robot, which preserves visual and angular ratios as seen from the platform stage. In 2011, before and during the excavation season, twenty prominent pictographs, and 280 points on the outcrop surface were laser distance measured from the platform stage, and cardinal directions as well as inclination (altitude) readings were verified with a Leica disto 8 laser distance measure and a TopCom theodolite station. Previous compass readings in 2007–2008 had to be corrected to true north, which for Monte Alegre's magnetic declination in 2008, was a correction of + 18°01’±19’ [verified using 5]. All electronic devices (GPS and Theodolite) were set to automatically correct for true north at the time of reading, however, a variance of 0–5° intermittently reoccurred among the different devices. This variance may have been due to human error, inclination of the units, and local electronic or magnetic interference. Radiocarbon dating of gymnosperm wood charcoal was performed by accelerated mass spectrometry at the University of Arizona NSF-Arizona AMS Laboratory in late 2012 and early 2013. Sample masses varied between 0.4 to 1.97 mg. Calibration curves were calculated with OxCal version 4.2.3 (IntCal 09) in 2013 and recalibrated (IntCal 13) in 2016.

Discussion A few rock art sites from the terminal Pleistocene to early Holocene periods have been recently discovered in Brazil [4, 6–9]. Other sites, presumed to be more recent, have been investigated for their potential archaeoastronomy alignments as well [10], like the megaliths near Calçoene, Amapa [11], or the prolific grooves and cupules at Pedra da Inga in Paraiba [12]. Yet, the most interesting similarities to Painel do Pilão rock art can be found among the São Francisco art tradition from site: BA-RC-28, located in Coribe, Bahia—Brazil. There, pictographs depict numerous long vertical lines and rectangular grids that similarly may reflect a tally system of sky observations [13–15]. Even as far south as Santa Catarina Island in Florianopolis, Brazil, some rock art petroglyphs may depict tallies and diamond lattice patterns—theorized [16] to represent fishing nets—do share compositional similarities to the right-side portion of the Painel do Pilão grid. Another stylistic and motif-themed similarity is found among the Agreste tradition from Pedra do Velho, Samuel in Paraiba, Brazil, where 3-digit stick figures of probable turtles and lizards are depicted crowding around a concentric circle [13, 14]. These drawings are similar to some of the zoomorphic pictographs at Painel do Pilão and throughout Monte Alegre rock art sites, especially at the other open-air site named Mirante. A number of other pictograph motifs throughout Monte Alegre share some similarities to rock art sites throughout Pará, Brazil [17] but many of those similarites can be seen in the posture of the humanoid stick figures. There seem to be less sky-themed images at other Pará sites, and several sites have petroglyphs instead of pictographs. Regardless, although specific dates remain elusive, the dispersal of sites suggest a widespread practice of shared knowledge and artistic influences [6, 17]. In no way can or should all the images at Painel do Pilão be considered to have preserved since the paleoindian period 13,000 years ago. Image enhancements of the grid shows evidence of earlier designs, but currently there is no way to determine how much time elapsed between overlapping paint strokes. The excavation recovered lithic deposits in nearly all levels but the few reliable charcoal samples from higher levels have not yet been analyzed. Charcoal from wall fall, that almost certainly fell from close to the surface, was dated to 2,112 ± 40 yr BP (2251–1989 cal yr BP OxCal 4.2 IntCal09). Therefore it is likely that some painted images (possibly the 12 yellow handprints overlaying the red pictographs on the lower panel) were produced recently. However, the data presented here lays a case for initial painting to have begun around the time that the area was first inhabited 13,000 years ago, and that those earliest images, which were probably retouched or traced more recently, were position in the most prominent wall locations and height visible from the stage. These images have, and are somewhat bound by, the horizon azimuthal markings of sunrises and possibly sunsets between solstices in a solar year. While a matrix of lollipop images, and a few others that are paired, align to 66° azimuth, a few single isolated lollipop images (5 out of 18 total) do not, therefore, the motif might not represent the sun. They could represent certain stars along the ecliptic, planets, the moon, or constellations; all these theories (especially Mercury and Venus) the author explored with the StarryNight sky simulator but found little correlation. Another alternative theory difficult to test is that the lollipop images represent the maracas of individuals who may have pilgrimaged to the site. Maracas are sited as being symbolically and spiritually vital to contact period Brazilian cultures [18, 19], utilized by shaman [20], but also by layman during dances and ceremonies [21, 22]. However, if they represent maracas—symbolic of personal identities—we might expect them to be adjacent to similar personal identifiers, like the twenty-in-all red and yellow painted handprints; yet, they are not. Also, this alternative theory does not address why 13 of the 18 lollipops align near the solstice sunrise. Of the other 5 lollipops, two on the upper ledge face the sun as it rises higher in the sky during the days around the same solstice, and a third one, located north of the grid on the lower panel, is not a "true" lollipop" because it is "animated" by the addition of horns and legs. Therefore, the horizon sun assignments provide the strongest evidence, further strengthened by the painted red equinox circle. The painted circle underneath the outcrop above the excavation unit is oriented to ~90°, and under initial considerations it is difficult to understand how the equinox would have been determined by naked-eye astronomers unless they had counted the total number of days between solstices to compute the half-way mark. Ethnographic accounts of Amazonian indians suggest that more importance was given to the day of the year when the sun cast no shadow from a gnomon at midday [23, 24]. Such an event only occurs for just one day of the year near midday when the sun passes through the exact zenith of the sky for a given location that must lie near the equator at lattitudes between the tropics. Monte Alegre, at 2°3' south, meets this criterion. However, the day this occurs there is not on the day of the equinox. Presently, this day of virtually no shadow occurs on March 15 and September 28, about seven days away from the equinox. On these days at about 12:28 PM, the sun reaches the exact zenith at 89.9° altitude [calculated for the year AD 2010 from the 25], casting virtually no shadows. On those days, however, the sun rises on the horizon at ~92°, not 90°. Even 13,000 years ago, according to StarryNight software's reconstructed ancient sky, the sun would have rose in the morning at 91.48° local azimuth on the day it passed exactly through the zenith, thereby casting no shadows (accounting for obliquity and precession). Neither ancient nor modern dates for the shadow phenomenon occur on the equinox, and neither coincide with a horizon alignment of 90°. That alignment occurs on the day of the true equinox, so the painted circle must truly have been placed to mark sunrise on the day of the true equinox, however and whenever the artists painted it there.

Conclusion Recognizing the passage of the seasons is perhaps something taken for granted in the northern or far southern latitudes because there are so many obvious signs. However, tropical environments—like at Monte Alegre just 2° south of the equator—do not have any of those telltale higher lattitude signs. There are no major changes in temperature, no changes of precipitation from rain to snow, no significantly shorter or longer days and nights, and no widespread coordinated shedding or color change of tree foliage. Therefore, the passage of the seasons—i.e. a solar year—is perhaps most recognizable by tracking the migration of the sun between southern and northern solstices. To do this, however, one needs a clear view of the horizon—which is usually difficult in a rainforest environment—but Monte Alegre provides the necessary elevation above the forest canopy to view the horizons. For paleoindian cultures, the river would have been the most efficient mode of travel, the hills at Monte Alegre offered lithic tools and horizon sightings, and once there, tracking the sun through rock art pictographs and tally marks allowed for them to mark the cyclic passage of time in a rudimentary calendar. Armed with this visual aide, the ancient Amazonians could better predict and schedule subsistence and social activities, like resource acquisition and ritual ceremonies. The results of this research have implications on the development of traditional astronomy knowledge systems extending to the terminal Pleistocene. This was a critical moment in history when our human ancestors were faced with rapid changes to the global climate. We do not know the extent to which paleoindians recognized these changes, but it is during this time period that Monte Alegre first shows evidence for paleoindians using rock paintings. I've argued here that the context of the rock paintings indicate a method of recording seasonal sky observations in pictographs with enough precision that it could have helped them predict cyclic patterns of resource availability in the local environment. Archaeoastronomy sites like at Painel do Pilão are pushing further back in antiquity the evidence for human use of astronomy observations to marke the passage of time. And even though specific rock drawings can not be pinpointed to over 13,000 years ago, this research helps establish that tropical cultures engaged and utilized sophisticated knowledge of astronomy maintained through rock art and possibly shared or reimagined by more recent cultures who either inherited or rediscovered the ancient paintings as they traveled far afield throughout eastern South America. Beyond the art and archaeoasronomy, the recovery of lithics and the reduction of a platform wall during the paleoindian period shows that the interior of the South American continent was being inhabited as early or earlier than many coastal sites. And the preence of rock art during that initial period suggests that rock art as a form of archaeorecording may have been an adaptive strategy consistent with pioneers who sought to familiarize themselves to a new landscape. Similar astronomy lore [26–28] is found among more recent cultures for village orientation and construction in Amazonia [24, 29–32] and the Andean regions of South America [33–36], for the layout of many platform plaza constructions in Mesoamerica [26, 37–39], and for the medicine wheels, gnomons, and sun dagger rock art of Sun-watcher chiefs in North America's southwest and plains cultures [40–43].

Supporting Information S1 File. Supporting Data Ser. A compilation of individual data sets, including excavation catalog, AMS carbon sample reports, and Sun alignment data tables. https://doi.org/10.1371/journal.pone.0167692.s001 (PDF)

Acknowledgments Special thanks to Carmen Davis, Anna Roosevelt, Laura Junker, Joel Palka, Vincent LaMotta, Virginia Miller, Waud Kracke, Robert Hall, and Denise Schaan, as well as the many Brazilian scholars and families that assisted my research: Marcio Amaral, Leonard Grala, Tiba, Nelci, and especially to Ozias and his extended family Creusa, Nildo, and Obede to name a few.

Author Contributions Conceptualization: CSD. Formal analysis: CSD. Funding acquisition: CSD. Investigation: CSD. Methodology: CSD. Validation: CSD. Visualization: CSD. Writing – original draft: CSD. Writing – review & editing: CSD.