Fossil Hominids: Stw 573 (Little Foot)

In 1995, Ronald Clarke and Phillip Tobias announced the discovery of the fossil Stw 573, nicknamed Little Foot, consisting of four articulating foot bones from an australopithecine. These bones were actually discovered in Sterkfontein Cave in the late 1970's, but were only recognized as hominid when Ronald Clarke found them while looking through a box of miscellaneous bones in 1994. The bones had human features in the hindfoot, while the forefoot was very apelike. Although adapted to bipedalism, the big toe could spread out sideways from the rest of the foot, like chimpanzees but unlike humans. Clarke and Tobias interpreted this as evidence that Little Foot had walked bipedally, but also spent a significant amount of time climbing in trees (Clarke and Tobias 1995, Oliwenstein 1995). Other scientists, most notably Owen Lovejoy, disagreed, arguing that the australopithecine hip, knee and spine are all adapted for bipedality, and that it is "mechanically and developmentally naive" to ignore all this evidence in favor of one foot joint.

Stw 573 skull In 1997, while examining more boxes of bones from Sterkfontein, Clarke found, over the space of about two weeks, another 8 leg and foot bones from the same individual. Because one of the bone fragments had a clean break that looked as though it could have been caused by miners blasting, Clarke suspected that more bones from the same individual might still be inside the cave. He asked two of the Sterkfontein preparators to search for a matching piece of bone in the exposed breccia surfaces of the cave. Amazingly, they found it, after two days of searching by the light of hand-held lamps. Further excavations found some more bones, and exposed the left side of a complete skull. The state of preservation and positioning of the bones already found indicated that a significant amount of the rest of the skeleton is probably still inside the rock, waiting to be extracted. (Clarke 1998)

Stw 573 hand By a year later, the bones of an almost complete arm and hand had been exposed, though not yet excavated from the rock. Clarke is very confident that more of the skeleton, including the pelvis and spine, remain inside the rock and can be retrieved. The skeleton was originally thought to be between 3.0 and 3.5 million years old. Partridge et al. (2003) claimed an age of 4 million years, which if correct would make Stw 573 one of the oldest known australopithecine fossils, and easily the oldest from South Africa. Walker et al. (2006) have determined an age of 2.2 million years.

The hand bones of Stw 573 seem to be like those of modern humans in being relatively unspecialized, having a short palm and fingers compared to modern apes. They lack the long, strong fingers used by chimps and gorillas for knucklewalking, and the elongation of the hand found in the highly arboreal gibbons and orang-utans. However the phalange (finger) bones which are visible from the side are curved like those of the Australopithecus afarensis skeleton Lucy, indicating they were probably used in climbing.

Additionally, Clarke considers that the feet of Stw 573 are a very good match for the 3.7 million year old footprint trails discovered at Laetoli by Mary Leakey's team.

Clarke points out (1998) that not only has this fossil yielded the most complete australopithecine skull yet found, it has been found in association with the most complete set of foot and leg bones known so far, with more probably still to be extracted from the rock (and since then, the arm and hand has been discovered.) In addition, the preservation of the skeleton is extraordinary, with most of the bones intact and joined together in their natural position (it is usual for fossil bones to be broken, often into small pieces, and for bones to get separated and scattered).

Clarke is not yet prepared to say which species it belongs to, except that it does appear to be an australopithecine. However, even from the bones that have been revealed so far, Little Foot looks like being at least as complete and important as Lucy, and will add tremendously to our knowledge of australopithecines. If Clarke's expectations of further finds are borne out, Little Foot could become the most spectacular and important hominid fossil ever discovered, rivalled only by the Turkana Boy Homo erectus skeleton.

References

Clarke R.J. and Tobias P.V. (1995): Sterkfontein member 2 foot bones of the oldest South African hominid. Science, 269:521-4.

Clarke R.J. (1998): First ever discovery of a well-preserved skull and associated skeleton of Australopithecus. South African Journal of Science, 94:460-4.

Clarke R.J. (1999): Discovery of the complete arm and hand of the 3.3 million-year-old Australopithecus skeleton from Sterkfontein. South African Journal of Science, 95:477-80.

Morris J.D. (1995): What distinguishes man from ape? Acts & Facts, 24.11:d (a creationist commentary)

Partridge T.C., Granger D.E., Caffee M.W., and Clarke R.J. (2003): Lower Pliocene hominid remains from Sterkfontein. Science, 300:607-12.

Oliwenstein L. (1995): New foot steps into walking debate. Science, 269:476-7. (Commentary on Clarke and Tobias 1995)

Walker, J., Cliff, R.A., Latham, A.G. (2006): U-Pb Isotopic Age of the StW 573 Hominid from Sterkfontein, South Africa. Science, 314:1592-4.

Links

Fossil find could rewrite human history, from BBC News, December 1998

African ape-man's hand unearthed, from BBC News, December 1999

Fossil find stirs human debate, from BBC News, January 2003

This page is part of the Fossil Hominids FAQ at the talk.origins Archive.