Discovery of complete arm and hand of the 3.3 million-year-old Australopithecus skeleton from Sterkfontein

RJ Clarke 1999 S Afr J Sci 95:477-480

... in 1978, Paul Abell discovered a hominid heel impression in 3.6-million-year-old volcanic tuff at Laetoli, Tanzania ...

The first few prints appeared very human and gave little hint of the revelations that were to come. In 1979, I was invited by Mary Leakey to continue the excavation and, as more footrpints were revealed, I was struck by their ape-like morphology with
slightly divergent big toe. In the prints of the larger individual there was, at regular distance behind the tip of each big toe, another toe-like impression that I interpreted as left by the metatarso-phalangeal joint. Subsequent study by Yvette
Deloison of several detailed casts that I had made of the prints led her not only to agree with my conclusions concerning the divergence of the big toe but also to make observations of her own that indicated a foot with ape-like characteristics. These
included weight-bearing on the lateral side of the foot, a prominent medial expansion of the abductor hallucis muscle, pointed heel, and absence of individual toe impressions apart from the hallux.

In 1985, my thoughts concerning the arboreal nature of the Laetoli footprints led me to arrange with the Boswell Wilkie Circus in Johannesburg for two of their chimpanzees, a female Pan paniscus and a male Pan troglodytes, to walk bipedally over wet sand.
The results were remarkable because, whereas the timid female walked nervously, digging her toes in and with widespread big toe, the male was confident and tended to walk with his big toe most often close to the other toes. The prints that he produced
have a strong resemblance to the Laetoli footprints and demonstrate that that the position of the hallux close to the other toes in a footprint does not mean that the owner of the foot could not diverge its hallux. It does, however, show that that when,
in this case, the chimpanzee walked bipedally in a confident manner it preferred to align its big toe with the others, presumably for more efficient locomotion. The Laetoli footprints could therefore have been made by feet with slightly divergent big
toes as represented by the Sterkfontein Australopithecus StW 573. One odd feature of the Laetoli prints is the absence of individual toe impressions apart from that of the hallux. Deloison has suggested that this absence of toe impressions indicates that
the toes were curled underneath, as is typical for the orang-utan when it walks bipedally.

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