Bipedalism is a fundamental modern human behavior yet many questions about its evolution in our extinct ancestors remain unanswered. Paleoanthropologists studying fossilized skeletal anatomy have analyzed these data in many different ways, only to arrive at conflicting conclusions regarding when and how bipedalism evolved. New approaches are necessary to resolve this ongoing debate.
Doctoral student Kevin Hatala (The George Washington University), under the supervision of Dr. Brian Richmond, will pursue a novel approach that circumvents these problems by analyzing a new type of 'fossilized behavior' data, in the form of recently discovered fossil hominin footprints. With a growing sample of fossil footprints from different times throughout the Plio-Pleistocene, these data can be used to investigate the evolution of human foot anatomy and bipedal locomotion. Before scientists can take advantage of the information stored in these footprints, however, there is need to determine how anatomy and gait are recorded in footprints. This study will use experimental biomechanics to investigate the dynamic process of footprint formation, and will apply this knowledge to the analysis of fossil hominin footprints from Laetoli, Tanzania; Ileret, Kenya; and Engare Sero, Tanzania. These analyses will directly test the hypothesis that modern humans' anatomical and functional adaptations for bipedal locomotion were present in hominins at 3.7, 1.5, and 0.12 million years ago, respectively.
Through collaboration with the Rutgers University/National Museums of Kenya Koobi Fora Field School, this project involves extensive training of undergraduates from Kenya, South Africa, and the US. Results will be presented to scientific audiences through publications and conferences, and to the public through ongoing collaborations with the Smithsonian's National Museum of Natural History Human Origins Program. A new archival system will be developed at the National Museums of Kenya, allowing students and other researchers to access the original three-dimensional scans of fossil footprints generated during this project.
In this project, a new approach was taken to study fossil human footprints from different geological time periods in order to better understand when and how a human-like form of bipedal walking first emerged. Controlled experiments to examine the dynamic process of footprint formation were conducted with a habitually barefoot Daasanach population from northwest Kenya. Volunteers made footprints in a setting in which we could measure various aspects of their anatomy, their movement patterns, and their foot function. We used photogrammetry to build 3-dimensional representations of each experimental footprint, and then used quantitative models to examine how biomechanical variables influence footprint shape. A set of analogous experiments was conducted with chimpanzees at Stony Brook University in order to understand how the mechanics of their bipedal locomotion, which are distinct from those of modern humans, are recorded in the shapes of their footprints. A famous set of 3.7 million year old hominin footprints from Laetoli, Tanzania and a set of 1.5 million year old hominin footprints recently discovered by us in Ileret, Kenya were then analyzed in light of those experimental results. Our objectives and their respective results were as follows: OBJECTIVE 1: Determine the influences of specific biomechanical variables on three-dimensional footprint shape in both humans and chimpanzees. Statistical modeling was used to examine how specific aspects of locomotion influence patterns of variation in footprint morphology. Biomechanical variables that significantly influenced patterns of footprint shape variation included motions at the hip, knee, and ankle joints and the distribution of pressure beneath the foot. These results link patterns of footprint morphological variation to specific biomechanical variables, including some that figure prominently in definitions of 'human-like' bipedalism. These results provide the first quantitative framework for inferring biomechanical variables related to locomotion from footprint assemblages in the human fossil record. OBJECTIVE 2: Using the results from human and chimpanzee experiments (Objective 1), develop functional interpretations of the c.3.7 Ma hominin footprints from Laetoli, Tanzania and the c.1.5 Ma footprints from lleret, Kenya. Determine whether either (or both) of these sites preserve evidence of human-like foot anatomy and function, and develop hypotheses about what these sites imply for other aspects of human evolution. The shapes of c.3.7 Ma fossil human footprints from Laetoli, Tanzania and c.1.5 Ma footprints from lleret, Kenya were quantified and compared to the shapes of footprints created by habitually barefoot modem humans. Functional interpretations could be made in the context of experimental results, relating patterns of variation in footprint morphology to specific biomechanical causes. Results indicate that the Laetoli footprints, which represent the only direct evidence of Pliocene hominin bipedalism, were likely produced by a different form of bipedalism than is seen in modem humans. The lleret footprints, however, which offer direct evidence of early Pleistocene hominin bipedalism, appear indistinct from the footprints of modem humans. These results support the hypothesis that important changes to fossil human locomotion (and therefore also their anatomy, behavior, and ecology) occurred near the late Pliocene or early Pleistocene. OBJECTIVE 3: Teach undergraduate students about the significance of the fossil footprint sites we are uncovering at Koobi Fora, Kenya, and how they advance our understanding of human evolution. Provide training to those students on the excavation, preservation, and analysis of fossil data, and provide some students with direct experience in excavating, documenting, and analyzing fossil human footprint sites. Through collaboration with the George Washington University/National Museums of Kenya Koobi Fora Field School, lectures on fossil human footprint sites, and their significance to our understanding of human evolution, were given to more than 40 undergraduate students from the US, Kenya, and South Africa during the 2013 and 2014 field seasons. Eight undergraduate students received intensive training on the excavation, documentation, and analysis of fossil human footprint sites, as they worked alongside us when collecting and analyzing fossil data. In addition to accomplishing these three main research objectives, this project led to the successful completion of a dissertation and Ph.D. training for the Co-PI. The Co-PI has presented results from this project at professional meetings and in published peer-reviewed papers, and he will continue to publish more results in the coming years. The results of this research have also been shared with the general public through several presentations at the Smithsonian National Museum of Natural History.
