Bipedality is one of the most distinguishing external characteristics that humans have. This article shows why/how a fossilized footprint is significant in the evolution evidence trail.
Early Humans Toed the Line http://sciencenow.sciencemag.org/cgi/content/full/sciencenow;2009/226/1
By Ann Gibbons
ScienceNOW Daily News
26 February 2009
More than 1.5 million years ago, several human ancestors wandered across a mud flat at what is now Ileret, Kenya. The footprints they left behind, the second oldest ever found, reveal that these early humans had evolved big, modern feet--and that they walked just like we do, according to a new study.
Human ancestors began walking upright at least 6 million years ago, according to analysis http://sciencenow.sciencemag.org/cgi/content/full/2005/318/3 hominid leg and pelvic bones. But researchers have debated when they evolved the ability to walk upright in a modern manner, rather than with a more primitive gait, possibly like the bent-kneed waddle of chimpanzees. Footprints found in Laetoli, Tanzania, show that the australopithecines that made them 3.75 million years ago had longer toes, a shallower arch, and a more apelike big toe that jutted slightly away from the other toes. This suggested to some that they had a more primitive gait and that the transition to fully modern walking didn't happen until our direct ancestor, Homo erectus, emerged about 1.9 million years ago. However, researchers had few fossils of the foot of H. erectus to prove it walked just like we do. Now, with the discovery of the footprints, which were probably made by H. erectus, at Ileret, they have direct evidence of how it walked.
To find out, a team led by Matthew Bennett of Bournemouth University in the United Kingdom scanned and digitized at least four trails of footprints laid down over several thousand years at Ileret. The researchers were able to use the size, spacing, and depth of the impressions to estimate the weight, stride length, and gait of the ancient walkers. As the researchers report in tomorrow's issue of Science http://www.sciencemag.org/cgi/content/abstract/323/5918/1197 the new footprints show that these early humans were pushing off the ground with their big toes--or toeing off--and shifting their weight over these digits in the same way as modern humans. H. erectus's feet had clearly evolved a modern shape, with the big toe parallel to the other toes and a pronounced arch, says paleoanthroologist Brian Richmond of George Washington University in Washington, D.C.
Other scientists agree that the prints expose the steps our ancestors took on the way to becoming modern. Fossil footprints are literally frozen behavior, says anatomist William Jungers of Stony Brook University Medical Center in New York state. They confirm that a modern, humanlike, bipedal gait is present by at least 1.5 million years ago, with all the biomechanical nuances we associate with our own way of walking. But the shoulder and pelvis of H. erectus were still primitive, says Jungers, so the footprints also show that on the path to modernity, the foot led the way.
Here's the abstract of that article. Note the nine participating research institutions.
Early Hominin Foot Morphology Based on 1.5-Million-Year-Old Footprints from Ileret, Kenya
Matthew R. Bennett,1* John W.K. Harris,2 Brian G. Richmond,3,4 David R. Braun,5 Emma Mbua,6 Purity Kiura,6 Daniel Olago,7 Mzalendo Kibunjia,6 Christine Omuombo,7 Anna K. Behrensmeyer,8 David Huddart,9 Silvia Gonzalez9
Hominin footprints offer evidence about gait and foot shape, but their scarcity, combined with an inadequate hominin fossil record, hampers research on the evolution of the human gait. Here, we report hominin footprints in two sedimentary layers dated at 1.51 to 1.53 million years ago (Ma) at Ileret, Kenya, providing the oldest evidence of an essentially modern human-like foot anatomy, with a relatively adducted hallux, medial longitudinal arch, and medial weight transfer before push-off. The size of the Ileret footprints is consistent with stature and body mass estimates for Homo ergaster/erectus, and these prints are also morphologically distinct from the 3.75-million-year-old footprints at Laetoli, Tanzania. The Ileret prints show that by 1.5 Ma, hominins had evolved an essentially modern human foot function and style of bipedal locomotion.
1 School of Conservation Sciences, Bournemouth University, Poole, BH12 5BB, UK.
2 Department of Anthropology, Rutgers University, 131 George Street, New Brunswick, NJ 08901, USA.
3 Center for the Advanced Study of Hominid Paleobiology, Department of Anthropology, George Washington University, Washington, DC 20052, USA.
4 Human Origins Program, National Museum of Natural History, Smithsonian Institution, Washington, DC 20013-7012, USA.
5 Department of Archaeology, University of Cape Town, Private Bag, Rondebosch 7701, South Africa.
6 National Museums of Kenya, Post Office Box 40658-00100, Nairobi, Ken target="_blank">ya.
7 Department of Geology, University of Nairobi, Post Office Box 30197, Nairobi, Kenya.
8 Department of Paleobiology, MRC 121, National Museum of Natural History, Smithsonian Institution, Washington, DC, 20013-7012, USA.
9 School of Biological and Earth Sciences, Liverpool John Moores University, Liverpool, L3 3AF, UK