Abstract Little is known about the ice age human occupation of the Pacific Coast of Canada. Here we present the results of a targeted investigation of a late Pleistocene shoreline on Calvert Island, British Columbia. Drawing upon existing geomorphic information that sea level in the area was 2–3 m lower than present between 14,000 and 11,000 years ago, we began a systematic search for archaeological remains dating to this time period beneath intertidal beach sediments. During subsurface testing, we uncovered human footprints impressed into a 13,000-year-old paleosol beneath beach sands at archaeological site EjTa-4. To date, our investigations at this site have revealed a total of 29 footprints of at least three different sizes. The results presented here add to the growing body of information pertaining to the early deglaciation and associated human presence on the west coast of Canada at the end of the Last Glacial Maximum.

Citation: McLaren D, Fedje D, Dyck A, Mackie Q, Gauvreau A, Cohen J (2018) Terminal Pleistocene epoch human footprints from the Pacific coast of Canada. PLoS ONE 13(3): e0193522. https://doi.org/10.1371/journal.pone.0193522 Editor: Michael D. Petraglia, Max Planck Institute for the Science of Human History, GERMANY Received: September 26, 2017; Accepted: February 13, 2018; Published: March 28, 2018 Copyright: © 2018 McLaren 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 within the paper and its Supporting Information files. Funding: Funded by Tula Foundation, HALAP 2012-2017. https://tula.org/ to DM. The Tula Foundation provided funding for research expenses. The funders participated in meetings concerning the overall scope of this project. 'In kind' support was provided for transportation and accommodations while in the field. The funders encouraged us to pursue this line of investigation but had no role in the preparation of this manuscript. Competing interests: The authors have declared that no competing interests exist.

Methods The beach in front of EjTa-4 was accessed by watercraft from the Hakai Institute facilities on Calvert Island. The field crew included academic and professional archaeologists, representatives from the Heiltsuk First Nation and Wuikinuxv First Nation, and students from the University of Victoria. A 7 cm diameter auger was used for initial sediment sampling, otherwise subsurface examinations were conducted using 50 x 50 cm trowel tests. A 4 x 2 m area was excavated by trowel in natural strata where late Pleistocene aged deposits were identified during initial testing. In situ artifacts, faunal remains, plant macrofossils, and features were mapped using line levels and tape measures. Excavated sediments were water screened through 3 and 6 mm mesh. Bulk sediment samples were taken in association with individual strata, footprints, other features and in situ artifacts. Measurements of the revealed footprints were undertaken in the field and included length of the central axis (from the heel to the distal edge of the second phalanx) and maximum width of the ball of the foot as outlined in Bennett and Morse [5]. Following Marty et al. [58] we draw on the following terminology to describe the footprints found at EjTa-4. The term ‘track’ refers to the footprint impression in general and here we use it interchangeably with ‘footprint’. ‘True track’ refers to the cast created by sediment displacement caused by the foot. ‘Under track sediments’ are beneath the true track. The upper part of the undertrack sediments may be compressed and have materials (plant macrofossils, shell fragments etc.) from the surface pressed into them from the force of the foot applying pressure downwards. ‘Over track’ sediment refers to sediments that were deposited after the footprint impressions were made. ‘Track surface’ refers to the original paleo-surface that was walked across. The ‘displacement rim’ is created as a result of lateral sediment displacement when the foot presses down on the ground, and by the slight upwards pull around the true track when the foot is lifted out of the print. All collected materials were transported to the archaeological laboratories at the Hakai Institute on Quadra Island and the University of Victoria for cataloguing and analysis. Samples for radiocarbon dating were sent to the W.M. Keck Carbon Cycle Accelerator Mass Spectrometry Laboratory at the University of California, Irvine for analysis. Faunal remains were analyzed using the comparative collection at the University of Victoria Zooarchaeology lab. Lithics were analyzed drawing on the typology developed for the region by Rahemtulla [59]. Photographs of the tracks were digitally enhanced using the D-stretch plugin for Imagej [60], a freeware image processing and analysis program. Some sediments were subsampled and prepared for light microscopic identification of sediment sphericity, pollen, spores, diatoms and other micro-organisms. Light microscope transects were conducted on the slides using 400X and 1000X magnification to detect the presence or absence of these and to identify those that were present. Samples of wood were identified to taxon through cellular analysis, using a comparative collection and following standard texts [61–63]. Wood samples were analyzed using high-powered microscopy viewed at 100X-800X magnification.

Discussion Based on the clear arch, toe and offset heel attributes of the tracks found during excavations at EjTa-4 we are certain that they were left by human feet. Of the large land mammals that inhabit the area today, only the hind paw of black and grizzly bears is similar to human tracks [66]. Although rare on Calvert Island, bears are common on the coast of BC. Our field crew members are very familiar with bear footprints and keep a look out for them, to know if there is a bear in the area, for making decisions related to worker safety. The tracks excavated on Calvert Island have a clearly defined arch, lack characteristic claw marks, are not triangular in overall shape (rather the heels are offset to either the left or right), lack a long third phalanx (rather the first or second phalanx is longest), and they are overall narrower than bear tracks. In addition to the lack of bear hind tracks, no bear fore tracks were excavated. Overall, non-human tracks of any kind are lacking from the area that was excavated. However, the track surface is a paleosol which extends beyond the periphery of our excavations and it is possible that non-human tracks would be found were excavations to be extended horizontally. Variation of the footprint length and width measurements may be in part due to the slippery clay in which they were impressed [67]. Regardless of this, three measurement clusters corresponding to three different size classes suggest that there were at least three different individuals who left the footprints (Fig 12). Using a Brannock device measurement chart (a device commonly used to measure feet [68]), the footprint measurements correspond to modern day US shoe sizes of a junior size 8, a junior size one (or a woman’s size 3), and a woman’s size 8–9 (or man’s size 7–8). In some instances, toe marks were clearly visible in the track impressions. This suggests the likelihood that those who left them were not wearing shoes. In the case of a few of the tracks, no toe prints were visible, and it was speculated during excavation that this may be the result of some type of shoe being worn. This is particularly the case for Footprint #4 which is one of the clearest examples and yet lacked clear toe marks (Fig 19). However, by digitally enhancing photos of this footprint there are clear first and second phalanx forward drag marks and for this reason it is unlikely that the foot that made this impression was shod. In another case (Fig 20) an elongation of the heel of the foot was found, likely caused by the pedestrian slipping forward in the substrate as they walked across it. PPT PowerPoint slide

PowerPoint slide PNG larger image

larger image TIFF original image Download: Fig 19. Photograph showing track #4 which has discernable toe drag marks. This track was later pedestalled and removed to the lab. (Photo by Joanne McSporran). https://doi.org/10.1371/journal.pone.0193522.g019 PPT PowerPoint slide

PowerPoint slide PNG larger image

larger image TIFF original image Download: Fig 20. Photograph showing track #26 with an elongated heel as a result of the pedestrian slipping forwards while walking in the clayey substrate (Photo by Joanne McSporran). https://doi.org/10.1371/journal.pone.0193522.g020 While some famous footprint sites are trackways (linear path of consecutive footprints) [e.g. 7,69], the assemblage from Calvert Island is not linear. The footprints from EjTa-4 more likely represent a congregation site as defined by Morse et al. [70]. This type of pattern results from people concentrating their activities in an area and may be centered around a focal point. Many more partial track-like depressions were discerned during excavations at EjTa-4 than were recorded as definite footprints. These unrecorded features were too obscured by repeated over-trampling to definitely identify as human tracks. For this reason, the footprints reported on here are only those which could be isolated, excavated and clearly demonstrated to be human tracks. By measuring the azimuth of each of the footprints identified, a rose diagram was created which demonstrates that the individuals that left the tracks were predominantly facing in a north to north-westerly direction, up the beach to the vegetation line (Fig 21). Footprints 8 and 9 (Fig 6) are side-by-side left and right footprints suggestive of someone standing with their feet slightly apart and facing northwestwards and inland with their back to the prevailing winds. The footprints were impressed into a soil just above the paleo-shoreline, possibly by a group of people disembarking from watercraft and moving towards a drier central activity area to the north or northwest. PPT PowerPoint slide

PowerPoint slide PNG larger image

larger image TIFF original image Download: Fig 21. Diagram showing the relative percentage of track azimuth measurements. It is clear from this diagram that those who left the tracks were primarily facing and/or moving in a north to northwesterly direction. https://doi.org/10.1371/journal.pone.0193522.g021 Paleo-environmental studies reveal that glacial refugia capable of supporting large land animals and plants existed in different places on the outer Pacific coast of Canada and southeastern Alaska between 20,000 and 13,000 years ago [23–28]. However, archaeological evidence of human occupation from the same period and geographic region is lacking. The footprints from Calvert Island provide evidence of a human presence on the western margin of the Cordilleran Ice Sheet during the late Pleistocene period, 13,300–13,000 years ago. This time frame is slightly later than of the age of the Manis Mastodon site, situated at the southern end of the area that was influenced by the Cordilleran Ice Sheet [35]. It is anticipated that further targeted research using high-resolution sea level histories on the coast will reveal evidence sufficiently old enough to account for the 14,500 year old deposits found at Paisley Cave [41] or Monte Verde [43]. While the tracks are contemporaneous with the early Clovis complex, which dates between 13,100 and 12,700 cal BP [71], Clovis points have not been found on the coast of BC north of the lower Fraser Valley [72]. It is possible that the late Pleistocene inhabitants of the western margins of the Cordilleran Ice Sheet did not use Clovis technology but rather employed unfluted projectile points related to the Western Stemmed Tradition [41,73]. The paleo-environmental information from northern Calvert Island provides a context that supports our assertion that the footprints date to the late Pleistocene epoch. Evidence from eroding sedimentary exposures on the northwest side of Calvert Island reveal that it was not glaciated 15,000 cal BP [74]. After this time the northern part of the island was subject to a short local glacial advance from the slopes of Mount Buxton that ended 14,500 cal BP. This is consistent with our findings of a glacial clay at the base of our test at EjTa-4. Following this, there is evidence for the start of forest succession. Early post-glacial forest succession is characterized by a dominance of Pinus contorta trees [75]. Wood identified and dated from the tracks and track surface is consistently P. contorta and associated with a paleosol. Human trackways are rarely discovered by archaeologists. Pleistocene/Holocene transition human tracks have been reported on from three distinct places in the Americas. At the Pehuen Co site in Buenos Aires Province in Argentina, human tracks were found on sandstone platforms in the intertidal zone [76]. These are associated with an impressive array of tracks left by extinct Pleistocene-age mammals dating to 14,000 cal BP. A single footprint was found and recorded at the Monte Verde site in Chile which dates to approximately 14,600 cal BP [77]. Two human trackways left in tuff at Cuatrociénegas site in Mexico have been dated to 10,700 cal BP and 7,200 cal BP [78]. A set of 40,000-year-old human tracks from Central Mexico has been reported on [79], but it has since been shown that these features were probably not created by ancient humans but by recent quarrying activity [70]. There are several mid to late Holocene archaeological sites with human tracks reported on in North America north of Mexico [80]. The Holocene track sites come from a variety of contexts including caves, riparian areas, and a pithouse floor. It is likely tracks are a component of many archaeological sites but are missed or not recognized as a result of their overall ephemeral character. In the practice of archaeology there are multiple levels of evidence indicative of past human activity. Late Pleistocene sites in the Americas have often undergone intense scrutiny, in particular where the highest levels of evidence, for example human skeletal remains or diagnostic bifacial projectile points, are not present [81]. Alternatively, others have presented lower qualities of evidence, such as scratched or flaked animal bones, as bona fide evidence for the early human occupation of the Americas [82,83]. In this context, it becomes important to at least acknowledge and reflect on the level and quality of evidence being put forth [84,85]. The features discovered in association with Stratum X at EjTa-4 are clearly human tracks. Features which allow for the identification of these tracks include sediment displacement rims surrounding human-track shaped depressions with aspects of foot morphology including heels, arches, balls and, in some cases, individual toes. Pinus contorta wood is associated with both the base of the track impression and the track surface. Bracketing dates for the twig wood found in Stratum X and associated with the human tracks range from 13,317 to 12,633 cal BP. According to palynological studies from a nearby pond, Pinus contorta pollen accounts for 50% of the assemblage between 14,000 and 12,000 years ago, although it is also found in lesser abundance in later time periods [75]. Stratum IX, which overlies the track surface, is less securely dated, ranging from 12,640 to 5608 cal BP. This particular stratum has been compromised by root bioturbation and rill erosion. Stratum VIII which overlies uneroded sections of Stratum IX dates between 12,849–12,751 cal BP. The oldest date from Stratum IX and the date from the overlying Stratum VIII are similar and provide the upper constraining age for the footprints. Combined, the stratigraphic, paleo-environmental and sea level-based evidence supports the conservative date range of 13,317–12,633 cal BP for the footprints. A limitation of the evidence presented here is that outliers exist, in particular in Stratum IX which covers the track surface and which has undergone bioturbation and erosion in places. Based on our observations of the tracks and the results presented here we maintain that the quality of evidence for late Pleistocene occupation at EjTa-4 is robust and adds to the growing body of information on the early human occupation of the formerly glaciated coastal areas of northern North America [35,36,44]. It is very likely that additional tracks exist in areas surrounding the excavations conducted to date. We have elected to stop excavations at the site so that any remaining tracks remain undisturbed so that future researchers may be able to attempt duplication of the results presented here with more advanced methods.

Conclusion During subsurface testing directed toward uncovering late Pleistocene archaeological deposits, human footprints were discovered beneath active beach deposits in front of the Meay Channel I archaeology site (EjTa-4). Further investigation, through careful excavation, revealed a total of 29 human tracks in an area measuring 4 x 2 metres. It is likely that many more tracks exist in the surrounding and unexcavated sediments. Based on the length and width of these features, they appear to have been left by a minimum of three people, including one juvenile. Many more footprints were present but could not be accurately discerned or measured as a result of over-trampling. Preserved wood found on the track surface and pressed into the bottom of the tracks is identified as Pinus contorta. Radiocarbon ages on the wood sampled from the track surface and the bottom of the track impressions consistently date between 13,317 and 12,633 cal BP. The footprints found at EjTa-4 add to the growing body of evidence that humans inhabited the Pacific coast of Canada during late Pleistocene times.

Acknowledgments Funding and in-kind support was provided by the Tula Foundation and Hakai Institute. We thank Christina Munck and Eric Peterson for their involvement, guidance and assistance in all aspects of this project. We are grateful to the staff at the Hakai Institute for providing meals and accommodations. Many thanks to Harvey Humchitt, Kelly Brown of the Heiltsuk Integrated Resource Management Department for their guidance and to Jennifer Carpenter for providing comments on an earlier version of this manuscript. We acknowledge Peter Johnson of the Wuikinuxv First Nation for his input and support. Thanks to the researchers that helped in the field or lab including: Maxwell Johnson Jr., John Maxwell, Jennifer Walkus, Joanne McSporran, Farid Rahemtulla, Andrea Walkus, Jim Stafford, Aurora Skala, Joshua Vickers, Jess Barton, Cecilia Porter, Johnny Johnson, Seonaid Duffield, Callum Abbott, Brittany Witherspoon, Carling Reid, Alex Nichini, Alex Lausanne, Grant Callegari, Meigan Henry and Iain McKechnie. Thanks to John Southon and the W.M. Keck Carbon Cycle Accelerator Mass Spectrometry Laboratory at the University of California, Irvine, for running all radiocarbon date samples. All work was conducted under BC Archaeology Branch permit #2011–171 and BC Park Use Permits #105588 and #105935. We acknowledge Steve Acheson and Vashti Thiesson who were the BC Archaeology Branch project officers for this work. A preliminary version of this paper was presented at the Prehistoric Human Tracks conference (May 11–13, 2017) at the University of Cologne and Neanderthal Museum in Germany, and we are grateful for the insights and feedback given by trackers, archaeologists and ethnographers who attended. Many thanks to Neil Roach, Jon Erlandson and two anonymous scholars for their time and effort in conducting peer reviews for this paper.