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 discovered in Sterkfontein Cave in 1970’s, but were only recognized as hominid when Clarke found them while looking through a boxes of bovid and unclassified cercopithecoid bones in 1994. In 1997, while examining more boxes of bones from Sterkfontein, Clarke found another 8 leg and foot bones from the same individual. He then suspected that more bones from the same individual might still be inside the cave. He was right and the result was the discovery of quite a complete skeleton embedded in the breccias. The work to retrieve the remains is still underway. The materials recovered to date show that it is a fossil in an excellent state of conservation, the most complete of all hominins dated to around 3.5–3 Ma, on the basis of magnetochronology. While this is the most probable date, existing date estimates range from 4 Ma (based on cosmogenic 26Al and 10Be radiometric dating) to 2.2 Ma (based on uranium-lead dating). Taxonomic position of this fossil individual still remains unclear. It is definitely a form of Australopithecus, but it would be wise to wait for the complete extraction and description. Clarke (2008) thinks that Little Foot differs enough from A. africanus material that it could represent a second South African species of Australopithecus (represented in Sterkfontein Member 4 and Makapansgat deposits).

Stw 573 articulated foot bones (above), reconstruction of the foot (below).

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Partially excavated Little Foot’s skull (above).

Of course, the foot bones are what initially brought the attention of the scientific community. They include bones of the left foot:  talus, navicular (that articulates with the head of the talus), a medial cuneiform (that articulates with the distal surface of the navicular), and the proximal half of the first metatarsal of the foot’s big toe (articulated with the cuneiform) (Clarke and Tobias, 1995). In general, morphology of the Little Foot suggests a biped which supported the body’s weight on its lower limbs. But it allso reveals a mixture of apelike and humanlike traits; it shows the intermediate condition between human-like total bipedalism and arboreal activity. Talus is the closest bone to human morphology and navicular and medial cuneiform exhibit intermediate morphology, while the anterior of the foot seems more primitive. Tobias (1997) concluded: ‘‘It seems that the astragalus and the proximal ankle joint adopted the human form quite early on, whereas the anterior part of the foot retained its primitive state for a long time’’. The mobility of the big toe (opposable hallux) is an ape like trait. This could point to the (limited) ability of grasping branches while climbing trees, but some studies (HarcourtSmith, Aiello 2004) suggested that Little Foot actually could not oppose its hallux.

If you want to learn more about this fossil, I suggest you to read these articles:

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.

CLARKE, R.J.. (2008) Latest information on Sterkfontein’s Australopithecus skeleton and a new look at Australopithecus. South African Journal of Science 104: 443-449 (here is online link to the full article: http://www.scielo.org.za/pdf/sajs/v104n11-12/a1510412.pdf)

HarcourtSmith WEH, Aiello LC (2004) Fossils, feet and the evolution of bipedal locomotion. J Anat 204: 403–416

Tobias, P. (1997a) El descubrimiento de Little Foot y la luz que proporciona sobre co´mo los homı´nidos se volvieron bı´pedos. Ludus Vitalis 8, 3–20.

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