干旱区生态环境知识资源中心

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 cast African site of Laetoli. Tanzania. The Hawaiian footprint area encompasses about 13 km(2) of the Ka'u Desert. Two footprint-bearing 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 hearing 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.