D. Jeffrey Meldrum’s research while affiliated with Idaho State University and other places

The chimpanzee foot is flexible near its middle, it can bend about the axis of the transverse tarsal joint, whereas the human foot is a comparatively rigid arched platform. Flexion at the transverse tarsal joint—the ''midtarsal break''—uncouples the functions of a grasping, or prehensile, forefoot and a propulsive hindfoot during grasp-climbing on vertical or inclined supports. At some point after the transition to habitual bipedalism, these grasp-climbing adaptations were compromised by the evolution of the longitudinal arch, which permits increased mechanical advantage of the flexors of the ankle and im- proved endurance for long-distance walking and running. Ape, human, and Plio-Pleistocene hominid footprints were examined for the effects of a midtarsal break. The human footprint reflects arched-foot architecture, combined with a stiff-legged striding gait. Pressure releases occur at particular locations behind the ball and the great toe, or hallux. Early (ca. 3.5 million years ago) hominid footprints from the Laetoli excavation confirm midfoot flexibility, including repeated suggestion of an associated pressure ridge. The Terra Amata footprint (ca. 400,000 years ago), yet to be fully pub- lished, exhibits evidence of midfoot flexibility. Several footprints attributed to an alleged North American ape, commonly known as sasquatch, exhibit a distinctive midtarsal pressure ridge and other indications of midfoot flexibility. In the Patterson-Gimlin film, the feet of the film subject correlate with the kinematics inferred from the footprints, in that a midtarsal break is present. Additional independent examples corroborate the consistent presence of this feature, including examples of half-tracks that record contact beneath the foot only anterior to the midtarsus. These data provide a fresh perspective from which to consider the pattern and timing of the emer- gence of the distinctive features of modern human bipedalism and bear on the credibility of the possible existence of sasquatch. The observed and inferred sas- quatch locomotor anatomy parallels the stable adaptations that marked the greater span of early hominid bipedalism.

Fossilized footprints preserved in volcanic ash tuffs in the Hawaii Volcanoes National Park afford an exceptional opportunity to study footprints of traditionally unshod modern human pedestrians, laid down under conditions relatively similar to those associated with footprints made by Pliocene hominids at the east African site of Laetoli, Tanzania. The Hawaiian footprint area encompasses about 13 km2 of the Ka’u Desert. Two footprintbearing ash layers date to 200 and 400 years before present (ybp) respectively. The track localities were surveyed with GPS coordinates and photographed, including stereophotography. In many instances footprint clarity and preservation are exceptional, revealing anatomical details of foot shape, toe conformation and arch development. Footprints were contrasted with stereophotos and casts of the Laetoli tracks and with footprints made by a captive chimpanzee in a sand trackbox. The modern human footprints were distinct in the marked development of the ball of the foot and toe pads, indicative of differential weight bearing or traction by these structures. There is consistent expression of a well-developed arch and no indication of midtarsal flexion. In contrast, the Laetoli hominid tracks do not exhibit these adaptations. Instead, they display a tapering proximal heel outline, relatively narrow distal metatarsus, indistinct ball and poorly differentiated impressions of the lateral toes. Preservation of the ash layer is patchy throughout the Ka’u footprint area; however, several examples of tracks permit limited documentation of spontaneous gait parameters. Contrasts with the Laetoli tracks emphasize the short step length of the fossil hominid gait and the highly variable angle of gait and step width in both ancient hominid and modern human trackways.

Functional-morphological analyses related to fossil and contemporary hominin locomotion are the focus of this volume. As locomotion is considered a key element in the overall behavior of living primates, allowing them to fulfill such basic needs as avoiding predators, foraging for food, and finding mates, biological anthropologists have generally agreed that it most likely served similar functions in earlier hominins as well. In primates, differing locomotor behaviors and their impact on other biological complexes have produced a diverse range of behavioral and anatomical configurations. In turn, primate locomotion studies are diverse in their scope. Anthropologists interested in hominin locomotion frequently draw on primate and other animal locomotor studies in efforts to understand the complexities associated with the evolution of hominin locomotion. Through comparative analyses on musculo-skeletal structures, positional behavior, and the kinematic and kinetic components of body motion in settings ranging from dissection rooms, laboratories, and in the field, researchers have developed a wide variety of approaches and techniques for investigating the intricacies of locomotor movement in living contemporary hominins and their closest relatives.

The inspiration for this volume of contributed papers stemmed from conversations between the editors in front of Chuck Hilton's poster on the determinants of hominid walking speed, presented at thel998 meetings of the American Association of Physical Anthropologists (AAPA). Earlier at those meetings, Jeff Meldrum (with Roshna Wunderlich) had presented an alternate interpretation of the Laetoli footprints based on evidence of midfoot flexibility. As the discussion ensued we found convergence on a number of ideas about the nature of the evolution of modem human walking. From the continuation of that dialogue grew the proposal for a symposium which we called From Biped to Strider: the Emergence of Modem Human Walking. The symposium was held as a session of the 69th annual meeting of the AAPA, held in San Antonio, Texas in 2000. It seemed to us that the study of human bipedalism had become overshadowed by theoften polarized debates over whether australo­ pithecines were wholly terrestrial in habit, or retained a significant degree of arboreality.