From “’Lucy’ lived among close cousins: Discovery of foot fossil confirms two human ancestor species co-existed” (Physorg, March 28, 2012), we learn,
A team of scientists has announced the discovery of a 3.4 million-year-old partial foot from the Woranso-Mille area of the Afar region of Ethiopia. The fossil foot did not belong to a member of “Lucy’s” species, Australopithecus afarensis, the famous early human ancestor. Research on this new specimen indicates that more than one species of early human ancestor existed between 3 and 4 million years ago with different methods of locomotion.
The partial foot has not yet been assigned to a species due to the lack of associated skull and dental elements.
In “Ancient human ancestor had feet like an ape” (Nature, 28 March 2012), Brian Switek reports, “Fossil foot hints that tree-dwellers lived alongside species built for walking”:
The fossil, a partial foot, was found in 3.4-million-year-old rocks at Woranso-Mille in the Afar region of Ethiopia. Bones of the hominin Australopithecus afarensis — the species to which the famous ‘Lucy’ skeleton belongs — have also been found in this location and from the same period.
But unlike Au. afarensis, the latest find has an opposable big toe — rather like a thumb on the foot — that would have allowed the species to grasp branches while climbing.
This suggests, to some, that there might have been several routes to walking upright, as Lucy apparently did, on different timelines.
From “Newly discovered pre-human walked near ‘Lucy’: But new species was also a tree climber” (CBC News, Mar 28, 2012),
Like A. afarensis, the new species has characteristic features in two of its joints adapted to walking on two legs – features unique to hominins and not found in apes or monkeys.
But unlike A. afarensis and modern humans, the new hominin has no arch running from its heel to the ball of its foot, and therefore could not have walked long distances. The arch absorbs energy, allowing humans to apply a greater load to each foot while walking or running.
The big toe of the new species is also quite different from that of A. afarensis and modern humans.
“This [finding] is fascinating, and makes the evolution of this defining behaviour not a single, linear evolutionary event, but a far more complex affair,” Harcourt-Smith says.
Fascinating indeed. But we only have part of one foot. And it’s already complex.
Meanwhile, Bernard Woods says that the human genus’ origin is frustratingly unclear. This won’t make it simpler.