Little Foot Finally Extricated

Nature News is reporting on the excavation and description of "Little Foot," a fossil initially discovered twenty years ago by Ron Clarke, at Sterkfontein Cave, in South Africa.  Colin Barras writes:

After a tortuous 20-year-long excavation, a mysterious ancient skeleton is starting to give up its secrets about human evolution.

The first of a raft of papers about ‘Little Foot’ suggests that the fossil is a female who showed some of the earliest signs of human-like bipedal walking around 3.67 million years ago. She may also belong to a distinct species that most researchers haven’t previously recognized.

“It’s almost a miracle it’s come out intact,” says Robin Crompton, a musculoskeletal biologist at the University of Liverpool, UK, who has collaborated with the research team that excavated the skeleton.

Why has this task taken so long and why is it so important? Barras continues:

By late last year, Clarke’s team had successfully removed enough bones to reconstruct more than 90% of the skeleton, and the specimen was unveiled to the world. No other Australopithecus fossil comes close to that level of completeness. For comparison, the most famous Australopithecus — Lucy — is around 40% complete.

Clarke and colleagues have posted a number of papers on the BiorXiv biology pre-print server. One of the papers is titled "The skull of StW 573, a 3.67 Ma Australopithecus skeleton from Sterkfontein Caves, South Africa."  Because these papers are unpublished, they are open-access. 

As Clarke and Kuman notes, this fossil is unlike those of Australopithecus africanus, a species ubiquitous in South Africa but more closely resembles, in some ways, Au. afarensis (Lucy) and Au. anamensis, both of which are north east African variants of Australopithecus and are the earliest members of that genus.  The fossil has been included, taxonomically, with a species originally described by Raymond Dart in 1948: Australopithecus prometheus.  Given its early date, the researchers argue that it cannot be descended from Au afarensis but must be coeval with it.  This suggests that both are descendants of an earlier species that had a large home range. 

More pieces to the puzzle. 

New BioLogos Post: The Human Fossil Record, Part 4: Australopithecus Conquers the Landscape

My newest post for BioLogos is up: The Human Fossil Record, Part 4: Australopithecus Conquers the Landscape. It focuses on the appearance of early Australopithecus and the shift to full-time bipedality.

More Evidence For A Gradual Shift to Bipedalism

Discovery News has a story on work that is being done on early hominid locomotion. Jennifer Viegas writes:

Early human ancestors stopped swinging in trees and started walking on the ground sometime between 4.2 and 3.5 million years ago, according to a new study.

This key moment, when our ancestors became anatomically and behaviorally less ape-like, coincides with increased cooling, more defined seasonality, and a grassland growth spurt. All transformed former forest habitats into more varied ones, forcing our very early relatives to change their ways.

"With the trees being farther apart, it became energetically advantageous for hominids to cross the gaps bipedally," said Gabriele Macho, lead author of the study that was published in the latest issue of Folia Primatologica.

This follows on the heels (sorry) of the recent studies on Ardipithecus, where it was found that this hominid had a skeletal pattern that was adapted not just for the trees but for bipedal walking as well. How long was this pattern maintained? Viegas continues:

The scientists observed that the Australopithecus anamensis wrist bones exhibited pressure loads associated with modern arboreal animals. The analyzed Australopithecus afarensis bones conversely showed stress loads comparable to those of more terrestrial species, including modern humans.

The researchers concluded that the important shift in early hominid lifestyle happened around the time when A. afarensis first emerged.

A. anamensis is the form that followed, at least chronologically, Ardipithecus ramidus. Whether or not there is a direct ancestor/descendant relationship there, it is clear that the transitional elements in Ardipithecus were continued in the hominid line and that A. anamensis maintained a similar adaptation to the environment. The true changes in bipedalism and adaptation came with A. afarensis. This is yet another piece of the puzzle at this critical point in our history.

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