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This conclusion is based on the reconstruction of the foot skeleton of a female A. White and Gen Suwa of the University of California, as well as detailed footprint analysis by Russel Tuttle of the University of Chicago; he compared human and other bipedal animals such as bears and primates, including gaits and foot structure, and taking into account the use of footwear.
For gait Tuttle looked at the step length, stride length, stride width, and foot angle, and determined that A.
In 1978, Leakey's 1976 discovery of hominin tracks—"The Laetoli Footprints"—provided convincing evidence of bipedalism in Pliocene hominins and gained significant recognition by both scientists and laymen.
Although much debated, researchers have tentatively concluded that Australopithecus afarensis is the species of the three hominins who made the footprints at Laetoli.
Two dating techniques were used to arrive at the approximate age of the beds that make up the ground layers at Laetoli: potassium-argon dating and analysis of stratigraphy.
Based on these methods, the layers have been named as follows, starting with the deepest: Lower Laetolil Beds, Upper Laetolil Beds, Lower Ndolanya Beds, Upper Ndolanya Beds, Ogol lavas, Naibadad Beds, Olpiro Beds, and Ngaloba Beds; it is the ancient Laetolil Beds that contain the footprints trackway.
Analysis of the footprints and skeletal structure showed clear evidence that bipedalism preceded enlarged brains in hominins.
At a species level, the identity of the hominins who made the trace is obviously difficult to precisely construe; Australopithecus afarensis is the species most commonly proposed.
Analysis of the Laetoli footprints indicated the characteristics of obligate bipedalism: pronounced heel strike from deep impressions, lateral transmission of force from the heel to the base of the lateral metatarsal, a well-developed medial longitudinal arch, adducted big toe, and a deep impression for the big toe commensurate with toe-off.
Subsequently, older Ardipithecus ramidus fossils were found with features that suggest bipedalism.
With the footprints there were other discoveries excavated at Laetoli including hominin and animal skeletal remains.
However, recent study of the Sadiman volcano has shown that it is not a source for the Laetoli Footprints Tuff (Zaitsev et al. Soft rain cemented the ash-layer (15 cm thick) to tuff without destroying the prints. The hominin prints were produced by three individuals, one walking in the footprints of the other, making the preceding footprints difficult to recover.
As the tracks lead in the same direction, they might have been produced by a group visiting a waterhole together, but there is nothing—or very little (see below, Interpretation and significance)—to support the common assumption of a nuclear family.
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However, like the Lower Laetolil Beds, no date can be assigned to the Ndolanya Beds. No fauna or artifacts are known from the Naibadad Beds, but they are correlated with a bed layer at Olduvai Gorge based on mineral content.