Holocene Footprints in Namibia: The Influence of Substrate on Footprint Variability Sarita A. Morse, 1 * Matthew R. Bennett, 2 Cynthia Liutkus-Pierce, 3 Francis Thackeray, 4 Juliet McClymont, 1 Russell Savage, 1 and Robin H. Crompton 1 1 Institute of Ageing and Chronic Disease, University of Liverpool, Liverpool L69 3GE, UK 2 School of Applied Sciences, Bournemouth University, Fern Barrow BH12 5BB, UK 3 Appalachian State University, Boone, NC 28608 4 University of the Witwatersrand, Johannesburg, South Africa KEY WORDS footprints; human ichnology; bipedalism; Namibia; Ileret ABSTRACT We report a Holocene human and ani- mal footprint site from the Namib Sand Sea, south of Walvis Bay, Namibia. Using these data, we explore intratrail footprint variability associated with small var- iations in substrate properties using a “whole foot” ana- lytical technique developed for the studies in human ichnology. We demonstrate high levels of intratrail vari- ability as a result of variations in grain size, depositio- nal moisture content, and the degree of sediment disturbance, all of which determine the bearing capacity of the substrate. The two principal trails were examined, which had consistent stride and step lengths, and as such variations in print typology were primarily con- trolled by substrate rather than locomotor mechanics. Footprint typology varies with bearing capacity such that firm substrates show limited impressions associated with areas of peak plantar pressure, whereas softer sub- strates are associated with deep prints with narrow heels and reduced medial longitudinal arches. Sub- strates of medium bearing capacity give displacement rims and proximal movement of sediment, which obscures the true form of the medial longitudinal arch. A simple conceptual model is offered which summarizes these conclusions and is presented as a basis for further investigation into the control of substrate on footprint typology. The method, model, and results presented here are essential in the interpretation of any sites of greater paleoanthropological significance, such as recently reported from Ileret (1.5 Ma, Kenya; Bennett et al.: Sci- ence 323 (2009) 1197–1201). Am J Phys Anthropol 000:000–000, 2013. V C 2013 Wiley Periodicals, Inc. Since the discovery of the 3.66 Ma Laetoli footprints in the late 1970s (Leakey and Hay, 1979; Leakey and Harris, 1987, Deino, 2011), footprints have held a place in the paleoanthropological record. With each new dis- covery, the body of human footprint evidence has grown (Behrensmeyer and Laporte, 1981; Mietto et al., 2003; Avanzini et al., 2008; Bennett et al., 2009), but until recently the tools with which to objectively interpret this evidence have been limited. Fossil footprints, regardless of age, provide information about hominin presence and behavior, the evolution of bipedalism, and modern loco- motion (Lockley et al., 2008; Kim et al., 2008a,b; Bennett et al., 2009). Here, we use a new “whole-foot” analytical tool which attempts to remove some of the subjectivities which have hitherto hindered the interpretation of an- cient footprint sites (Crompton et al., 2012). In doing so, we hope to move the discipline away from simple site description adopted at many sites to date (Brown, 1947; Aldhouse-Green et al., 1992; Roberts et al., 1996a; Webb et al., 2006; Aramayo and Manera de Bianco, 2013, Kim et al., 2009; Schmincke et al., 1979) to a more forensic approach to unlock the true paleoanthropological poten- tial of human trace fossils (Allen, 1997; Tuttle, 2008). There are number of critical questions that need to be addressed to decipher the biomechanical signature within footprints not of least of which is the relationship between footprint depth and peak or duration of plantar pressure (D’Ao^ ut et al., 2010; Hatala et al., 2013; Rich- mond et al., 2012). However, here we focus on the role of the substrate. Before biomechanical inferences can be made from a footprint site animal or human, two key issues must be addressed. First, the control of substrate on print mor- phology (Laporte and Behrensmeyer 1980; Scrivner and Bottjer, 1986; Cohen et al., 1991, 1993; Allen, 1997; Bromley, 2001; Melchor et al., 2002, 2006; Manning, 2004; Mil an, 2006; Jackson et al., 2009; Marty et al., 2009) which affects the degree to which variation in sed- imentology may obscure the anatomical and biomechani- cal signature of the print maker. This is vital both when comparing prints from different sedimentological envi- ronments, as well as prints from within a single environ- ment (Mil an, 2006; Scott et al., 2007, 2008; Mil an and Grant sponsor: the Natural Environment Research Council in the UK; Grant number: NE/H004246/1; Grant sponsors: The Office of International Education and Development and the University Research Council at Appalachian State University, The Andrew W. Mellon Foundation. *Correspondence to: Sarita A. Morse, Institute of Ageing and Chronic Disease, University of Liverpool, Sherrington Building, Ashton Street, Liverpool, L69 3GE, UK. E-mail: sarita.morse@ gmail.com Received 20 May 2012; accepted 10 March 2013 DOI: 10.1002/ajpa.22276 Published online 00 Month 2013 in Wiley Online Library (wileyonlinelibrary.com). Ó 2013 WILEY PERIODICALS, INC. AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 00:000–000 (2013)