Abstract Investigations at Happisburgh, UK, have revealed the oldest known hominin footprint surface outside Africa at between ca. 1 million and 0.78 million years ago. The site has long been recognised for the preservation of sediments containing Early Pleistocene fauna and flora, but since 2005 has also yielded humanly made flint artefacts, extending the record of human occupation of northern Europe by at least 350,000 years. The sediments consist of sands, gravels and laminated silts laid down by a large river within the upper reaches of its estuary. In May 2013 extensive areas of the laminated sediments were exposed on the foreshore. On the surface of one of the laminated silt horizons a series of hollows was revealed in an area of ca. 12 m2. The surface was recorded using multi-image photogrammetry which showed that the hollows are distinctly elongated and the majority fall within the range of juvenile to adult hominin foot sizes. In many cases the arch and front/back of the foot can be identified and in one case the impression of toes can be seen. Using foot length to stature ratios, the hominins are estimated to have been between ca. 0.93 and 1.73 m in height, suggestive of a group of mixed ages. The orientation of the prints indicates movement in a southerly direction on mud-flats along the river edge. Early Pleistocene human fossils are extremely rare in Europe, with no evidence from the UK. The only known species in western Europe of a similar age is Homo antecessor, whose fossil remains have been found at Atapuerca, Spain. The foot sizes and estimated stature of the hominins from Happisburgh fall within the range derived from the fossil evidence of Homo antecessor.

Citation: Ashton N, Lewis SG, De Groote I, Duffy SM, Bates M, Bates R, et al. (2014) Hominin Footprints from Early Pleistocene Deposits at Happisburgh, UK. PLoS ONE 9(2): e88329. https://doi.org/10.1371/journal.pone.0088329 Editor: Michael D. Petraglia, University of Oxford, United Kingdom Received: November 25, 2013; Accepted: January 4, 2014; Published: February 7, 2014 Copyright: © 2014 Ashton 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. Funding: The research was funded by the Calleva Foundation as part of the Pathways to Ancient Britain Project. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: The authors declare that no competing interests exist.

Introduction The survival of early hominin footprints is extremely rare, but can provide critical information about bipedalism, posture, gait and the size of the hominins involved, often in the absence of skeletal evidence [1]–[8] (Figure 1). In cases where multiple footprints are preserved, the number of individuals, the sex and age range of the group and the activities can be inferred [4], [7], [9]–[10]. The earliest hominin footprints are preserved in volcanic ash at Laetoli in Tanzania. These provide evidence of bipedalism in Australopithecus afarensis dating to ca. 3.66 million years ago (My) [1], [11]–[13]. In the Early Pleistocene at ca. 1.5 My two sites have been discovered just to the east of Lake Turkana (Kenya) with footprints of Homo erectus or possibly Paranthropus boisei. The first site is in sediments of the Koobi Fora Formation where several hominin footprints are preserved along with those of other animals such as hippopotamus [2]. At the second site, footprints from six individuals have been discovered 70 km to the north at Ileret [7], [14]. Here a series of hominin footprints preserve anatomical details consistent with a forward-pointing large toe and clearly distinguished lateral arch. The footprints are larger than those at Laetoli, and suggest that by 1.5 My humans had developed an essentially modern walking gait and are argued to have reached a similar stature to modern humans [15]. PPT PowerPoint slide

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larger image TIFF original image Download: Figure 1. Map of Pleistocene footprint sites dating from prior to 40 ky in Africa and Eurasia. https://doi.org/10.1371/journal.pone.0088329.g001 Footprints from the Middle and Upper Pleistocene are equally rare. Three hominin footprint tracks have been preserved in volcanic tuff in the Roccamonfina area of southern Italy dating to ca. 350 ky informing about gait and stride length on steep slopes [4]. In South Africa the sites of Langebaan and Nahoon date to the last interglacial (ca. 125 ky) [3], [6]. At both sites the footprints have been preserved in calcareous eolianites and provide information about height and body build at a critical time when anatomically modern humans were first emerging. Finally, at Vârtop Cave in Romania the only recorded late Neanderthal footprint is preserved in calcareous mud dating to between 97 and 62 ky [5]. A number of factors contribute to the rarity of footprints in the archaeological record. The preservation of a footprint requires the combination of soft sediments to allow an imprint to be made, a low-energy environment in which minimal erosion of the imprinted surface takes place and rapid burial of the surface by sediments deposited in a low-energy setting, such as still to slow-flowing water or by air-fall deposition. A further consideration is the subsequent exposure of the footprint surface with minimal erosion of the features. Holocene coastal and estuarine environments are locations that seem to be favourable for footprint preservation, with good examples in the UK at Sefton and in the Severn estuary where footprint surfaces have been studied over the last 20 years [16]–[22]. Here we report on a footprint surface found in Early Pleistocene estuarine muds at Happisburgh, UK, where preservation is due to very similar processes to those of the Holocene sites (Figure 2a). At Happisburgh the footprint surfaces have been revealed because of coastal erosion of overlying cliffs. The estuarine sediments at Happisburgh are part of the Hill House Formation (HHF) and are Early Pleistocene in age, dating to between 1 and 0.78 My. They preserve indirect anatomical evidence of the first hominins in northern Europe. PPT PowerPoint slide

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larger image TIFF original image Download: Figure 2. Location of Happisburgh. a. Map of UK showing location of Happisburgh; b. Plan of Happisburgh Site 3, exposed and recorded foreshore sediments, location of footprint surface and of borehole HC; c. Schematic cross-section of recorded sediments from Happisburgh Site 3 through to borehole HC showing stratigraphic position of footprint surface. Beds h–k are shown for borehole HC as recorded by West [23]. https://doi.org/10.1371/journal.pone.0088329.g002

Discussion The footprint surface and the human activity that it represents can be placed within the context of the landscape at Happisburgh. The humans of mixed ages were moving in a southerly direction across the mudflats of a tidally influenced river within the upper reaches of its estuary. The mudflats were rapidly buried by tidal processes with further silts. From palynological analysis of adjoining sediments, the local vegetation consisted of a mosaic of open coniferous forest of pine (Pinus), spruce (Picea), with some birch (Betula). Alder (Alnus) was growing in wetter areas and there were patches of heath and grassland (See Information S1). This vegetation is characteristic of the cooler climate typically found at the beginning or end of an interglacial or during an interstadial period, and is consistent with genera previously identified from HC and HSB3. The Happisburgh footprints provide the first indication of the body size of the earliest humans in northern Europe within a broader Pleistocene context. The known hominins in Europe during the Early and Middle Pleistocene were Homo antecessor from Atapuerca [43]–[44], H. heidelbergensis (e.g. Mauer, Boxgrove) or early H. neanderthalensis (e.g. Sima de los Huesos, Swanscombe) [45]. The evidence from Happisburgh suggests statures as large as ca. 1.73 m. As nine of the footprints indicate statures below 1.4 m, only three of the measured footprints might be considered as adults (1.60, 1.63 and 1.73 m). The adult stature estimates fall within the range of Homo antecessor [41] but also of Homo heidelbergensis and early and late Neanderthals [42]. Stature estimates based on the tali of Homo antecessor [41] show a mean stature of 1.73 m for male individuals and 1.68 m for female individuals. Recent stature estimates based on three samples of long bones from Sima de los Huesos, from other Neanderthal fossils and from early anatomically modern humans show mean values of 1.62, 1.61 and 1.78 m respectively [42]. The stature estimate of 1.73 m from the largest Happisburgh footprint might therefore possibly indicate a male. The foot index (mean = 39) for the Happisburgh individuals can be compared with other past and present populations. The index is similar to Native Americans (index = 39.61) [37] and Akiak Inuit (index = 38.260) [38], but narrower than those reported for modern humans from Mexico (index adults = 44.76, juveniles = 49.58) [46], the Vârtop Neanderthal (index = 48.18) [5] and the Middle Pleistocene footprints from Italy (index = 50) [4]. The Happisburgh footprints are slightly wider than the Kenyan footprints made by Homo erectus or Paranthropus boisei (index = 36.59) [15]. Overall the estimated foot size, foot area and stature of the Happisburgh hominins correspond with the estimates for Homo antecessor.

Conclusion Happisburgh has the earliest evidence of hominin footprints outside Africa, dating to between ca. 1 and 0.78 My with estimated body dimensions that fall within the range of the evidence from Homo antecessor fossils. The analyses suggest a group of at least five adults and juveniles walking along the mudflats of a large river. The rarity of such evidence is equalled only by its fragility at Happisburgh, where severe coastal erosion is both revealing and rapidly destroying sites that are of international significance. The pre-glacial succession around Happisburgh has now revealed several archaeological locations of Early Pleistocene and early Middle Pleistocene age with evidence of flint artefacts, cut-marked bones and footprints. Importantly, the sites are associated with a rich environmental record of flora and fauna allowing detailed reconstructions of the human habitats and the potential for preservation of organic artefacts. Continuing erosion of the coastline will reveal further exposures of the HHF and new sites, which promise to transform our understanding of the earliest human occupation of northern latitudes.

Supporting Information Information S1. Supplementary Information is provided for methods on Multi-Image Photogrammetry, the footprint analyses and pollen analysis. https://doi.org/10.1371/journal.pone.0088329.s001 (DOCX)

Acknowledgments We would like to thank Tim Albins and Nigel Larkin for help and advice in recording the surface together with Clive and Sue Stockton, Malcolm Kirby, Mike Chambers and the people of Happisburgh for their continued support. We are also grateful to David Waterhouse and John Davies of Norfolk Museums and Archaeology Service and to Brian Farrow and Russell Tanner of North Norfolk District Council for logistical help in the Project. Finally we thank the Calleva Foundation for support of the Pathways to Ancient Britain Project of which the research at Happisburgh forms a part.

Author Contributions Conceived and designed the experiments: NA SGL S. Parfitt MB RB PH CS. Performed the experiments: NA SGL S. Parfitt PH MB RB SMD CW. Analyzed the data: NA SGL S. Parfitt IDG SMD ML S. Peglar CS. Contributed reagents/materials/analysis tools: SMD ML S. Peglar CW. Wrote the paper: NA SGL IDG SMD MB RB PH ML S. Parfitt S. Peglar CW CS.