Journal of Human Evolution 64 (2013) 556e568 Contents lists available at SciVerse ScienceDirect Journal of Human Evolution journal homepage: www.elsevier.com/locate/jhevol Hominin stature, body mass, and walking speed estimates based on 1.5 million-year-old fossil footprints at Ileret, Kenya Heather L. Dingwall a,*,1, Kevin G. Hatala a,b, Roshna E. Wunderlich c, Brian G. Richmond a,d,* a Center for the Advanced Study of Hominid Paleobiology, Department of Anthropology, The George Washington University, 2110 G St. NW, Washington, DC 20052, USA b Hominid Paleobiology Doctoral Program, The George Washington University, 2110 G St. NW, Washington, DC 20052, USA c Department of Biology, James Madison University, MSC 7801 Harrisonburg, VA 22807, USA d Human Origins Program, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560, USA article info abstract Article history: The early Pleistocene marks a period of major transition in hominin body form, including increases in Received 30 April 2012 body mass and stature relative to earlier hominins. However, because complete postcranial fossils with Accepted 11 February 2013 reliable taxonomic attributions are rare, efforts to estimate hominin mass and stature are complicated by Available online 22 March 2013 the frequent albeit necessary use of isolated, and often fragmentary, skeletal elements. The recent dis- covery of 1.52 million year old hominin footprints from multiple horizons in Ileret, Kenya, provides new Keywords: data on the complete foot size of early Pleistocene hominins as well as stride lengths and other char- Bipedalism acteristics of their gaits. This study reports the results of controlled experiments with habitually unshod Body size Homo Daasanach adults from Ileret to examine the relationships between stride length and speed, and also fi Human evolution those between footprint size, body mass, and stature. Based on signi cant relationships among Pleistocene these variables, we estimate travel speeds ranging between 0.45 m/s and 2.2 m/s from the fossil hominin footprint trails at Ileret. The fossil footprints of seven individuals show evidence of heavy (mean ¼ 50.0 kg; range: 41.5e60.3 kg) and tall individuals (mean ¼ 169.5 cm; range: 152.6e185.8 cm), suggesting that these prints were most likely made by Homo erectus and/or male Paranthropus boisei. The large sizes of these footprints provide strong evidence that hominin body size increased during the early Pleistocene. Ó 2013 Elsevier Ltd. All rights reserved. Introduction Australopiths are estimated to have been relatively small compared with early Homo erectus or Homo ergaster (hereafter The late Pliocene and early Pleistocene mark a major transitional ‘H. erectus’). Based on hindlimb joint size, which is arguably one of stage in hominin evolution, with derived anatomical changes the best means of predicting body mass (e.g., Jungers, 1988a; Ruff, within the genus Homo including increased brain and body size, 2003; Gordon, 2004), Australopithecus afarensis specimens have potentially with decreased sexual dimorphism, reduced tooth size been estimated at 45 kg for inferred males and 29 kg for inferred suggesting dietary shifts, and elongated lower limbs that likely females (McHenry, 1992). Average stature for A. afarensis is also improved speed and energetic efficiency (Wood and Collard, 1999; small, with male and female estimates averaging about 151 cm and McHenry and Coffing, 2000; Wood and Richmond, 2000). The 105 cm, respectively (McHenry, 1991; McHenry and Coffing, 2000). increased body size and relative lower limb length (but see Pontzer, From these mass and stature predictions, as well as studies of size 2012) that distinguished some early Homo from Australopithecus and shape variation, it is clear that A. afarensis exhibited substantial resulted in a more derived hominin body shape that falls within the sexual dimorphism with regard to body size (Richmond and range of variation exhibited by modern humans (Richmond et al., Jungers, 1995; Lockwood et al., 1996; Plavcan et al., 2005; Scott 2002; Ruff, 2002). and Stroik, 2006; Gordon et al., 2008, 2010; contra Reno et al., 2003). Homo habilis estimates are also small, with male mean body mass and stature estimated at 37 kg and 131 cm, respectively. * Corresponding authors. Average female mass is estimated at 32 kg and stature at 100 cm E-mail addresses: [email protected] (H.L. Dingwall), kevin.g.hatala@ (McHenry, 1991; McHenry, 1992; re-analyzed in McHenry and gmail.com (K.G. Hatala), [email protected] (R.E. Wunderlich), [email protected] Coffing, 2000 excluding KNM-ER 1472 and 1481). It should be (B.G. Richmond). fl 1 Present address: Department of Human Evolutionary Biology, Harvard Uni- noted that although these body size calculations are in uenced by versity, 11 Divinity Ave., Cambridge, MA 02138, USA. the dearth of postcrania that can be reliably attributed to H. habilis, 0047-2484/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jhevol.2013.02.004 H.L. Dingwall et al. / Journal of Human Evolution 64 (2013) 556e568 557 cranial size variation is consistent with small overall body size shorter and earlier period of growth relative to modern humans, in H. habilis s.s. On the other hand, mean estimates of H. erectus Graves et al. (2010) argue that KNM-WT 15000 was 154 cm tall at stature (male: 180 cm, female: 160 cm; Ruff and Walker, 1993) and his time of death and would have attained an adult stature of only mass (male: 66 kg, female: 56 kg; Ruff et al., 1997) suggest that the 163 cm. This estimate is lower than that based on Ruff’s (2007) substantial increase in East African hominin body size that took analysis, closer to Ruff and Walker’s (1993) average stature esti- place during the early Pleistocene occurred with the appearance of mates for female H. erectus and not much larger than McHenry’s the earliest H. erectus around 1.9 Ma. These estimates suggest an (1991) male stature estimates of A. afarensis. Ohman et al. (2002) especially significant increase in female hominin body size and a similarly claim that Ruff and Walker (1993) overestimated KNM- concomitant decrease in the level of sexual dimorphism in WT 15000’s stature at death. They propose a new estimate of H. erectus relative to earlier hominins. 147 cm, which they argue accounts for axial/appendicular pro- However, several recent discoveries of small cranial remains portions in H. erectus that differ from those of modern reference belonging to H. erectus, for example from Olorgesailie (Potts et al., populations. Based on newly identified rib and vertebral fragments, 2004) and Ileret, Kenya (Spoor et al., 2007), and postcranial re- Haeusler et al. (2011) conclude that the rib cage of KNM-WT 15000 mains from Dmanisi, Georgia (Lordkipanidze et al., 2007) and Gona, was symmetrical and question previous interpretations that scoli- Ethiopia (Simpson et al., 2008) suggest that H. erectus may have osis or other pathologies affected the skeleton. This, in turn, sug- shown considerably more size variation than previously thought. gests that disease may not have affected KNM-WT 15000’s Furthermore, the presence of these small H. erectus specimens proportions and supports Ruff and Walker’s (1993) original size raises questions about whether body size dimorphism in H. erectus estimates. It is clear from these and other studies that stature and was appreciably different than that of earlier hominins (Antón, mass in H. erectus are the subject of ongoing debate. Body size es- 2012). The recent discoveries at Dmanisi include postcranial ma- timates in other early Pleistocene hominins are even more uncer- terial from three adults and one adolescent attributed to H. erectus. tain given the scarcity of well-preserved long bones with confident Stature and body mass have been estimated for two of the adults, attributions to H. habilis or Paranthropus boisei (McHenry and which imply smaller adult body sizes than those predicted from Coffing, 2000). other H. erectus material. Stature estimates based on humeral, Conclusions about temporal trends in hominin body size have femoral, and tibial measurements for a ‘large’ adult individual from implications for the formulation of hypotheses about other aspects Dmanisi averaged 149.3 cm, while estimates of stature derived of hominin evolution, many of which are concerned with the shift to from the first metatarsal of a smaller adult individual yielded an more xeric climatic conditions in East Africa throughout the early estimate of 143 cm (Lordkipanidze et al., 2007). Body mass esti- Pleistocene (McHenry and Coffing, 2000; Antón, 2003; Bobe, 2011). mates for the larger individual based on joint dimensions of the Evidence of increased mass and stature lies at the heart of hypoth- humerus, femur, and tibia, averaged 48.8 kg. The smaller in- eses regarding behavioral and physiological changes in early Homo dividual’s mass was estimated at 40.2 kg based on first metatarsal (McHenry, 1994; McHenry and Coffing, 2000; Aiello and Key, 2002; joint surface dimensions (Lordkipanidze et al., 2007). A pelvis from Aiello and Wells, 2002; Lieberman et al., 2009; Pontzer, 2012). The Gona, attributed to an adult female H. erectus individual, has pro- early Pleistocene falls temporally between the Pliocene, character- duced stature estimates between 123 cm and 146 cm based on an ized by smaller-bodied hominins (australopiths and H. habilis s.s.), estimated femur length using the three major articular surfaces and the later Pleistocene, with species of Homo that certainly had preserved in the pelvis (Simpson et al., 2008). These estimates from larger body sizes (Grine et al.,1995; Carretero et al., 2012). Because of Dmanisi and Gona are all smaller than the male and female aver- the limited sample of hominin fossils known from the early Pleis- ages predicted for H. erectus prior to these discoveries (Ruff and tocene (between 2.0 and 1.0 Ma), and the further paucity of fossils Walker, 1993).