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‘Little Foot’ skeleton analysis reignites debate over the hominid’s species

Researchers disagree over resurrecting a defunct species name

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6:00am, December 12, 2018
Ron Clarke

FOSSIL PUZZLE  Paleoanthropologist Ron Clarke excavates the skull of a hominid skeleton known as Little Foot. Controversial new investigations of the adult female conclude that she lived in southern Africa nearly 3.7 million years ago and belonged to a species that many researchers don’t regard as valid.

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A nearly complete hominid skeleton known as Little Foot has finally been largely freed from the stony shell in which it was discovered in a South African cave more than 20 years ago. And in the first formal analyses of the fossils, researchers say the 3.67-million-year-old Little Foot belonged to its own species.

In four papers posted online at bioRxiv.org between November 29 and December 5, paleoanthropologist Ronald Clarke of the University of the Witwatersrand in Johannesburg and colleagues assign Little Foot to a previously proposed species, Australopithecus prometheus, that has failed to gain traction among many researchers.

Clarke has held that controversial view for more than a decade (SN: 5/2/15, p. 8). He found the first of Little Foot’s remains in a storage box of fossils from a site called Sterkfontein in 1994. Excavations of the rest of the skeleton began in 1997.

Many other researchers, however, regard Little Foot as an early member of a hominid species called Australopithecus africanus. Anthropologist Raymond Dart first identified A. africanus in 1924 from an ancient youngster’s skull called the Taung Child. Hundreds of A. africanus fossils have since been found in South African caves, including Sterkfontein. One of those caves, Makapansgat, produced a partial braincase that Dart assigned to A. prometheus in 1948. But Dart dropped that label after 1955, assigning the braincase and another Makapansgat fossil to A. africanus.

Based on their research, Clarke and colleagues say that Little Foot’s distinctive skeleton, an adult female that is at least 90 percent complete, justifies reviving the rejected species. “Little Foot fits comfortably in A. prometheus,” Clarke says.

The estimated ages of Little Foot and additional fossils from Sterkfontein and Makapansgat, he says, indicate that A. prometheus survived for at least a million years and lived alongside the younger A. africanus for at least a few hundred thousand years. The new papers will appear along with several other new analyses of Little Foot’s skeleton in an upcoming Journal of Human Evolution.

The team’s claims, however, are still controversial. The papers “fail to make a sound case” for a second Sterkfontein species, says paleoanthropologist Bernard Wood of George Washington University in Washington, D.C.

In a comment scheduled for publication in the American Journal of Physical Anthropology, paleoanthropologists Lee Berger of the University of the Witwatersrand and John Hawks of the University of Wisconsin–Madison argue that Dart correctly discarded A. prometheus because he never clearly distinguished it from A. africanus. “I’m keeping an open mind, but I haven’t seen data [in the papers] to support any grand ideas about Little Foot,” Hawks says.

In one new study, Clarke and Witwatersrand colleague Kathleen Kuman describe skull features that the duo says set Little Foot apart from A. africanus. For example, the researchers point to the vertical sides of Little Foot’s braincase relative to A. africanus’ sloping sides and to heavily worn teeth from the front of the mouth to the first molars. Such wear probably resulted from eating tubers, leaves and fruits with tough skins, Clarke says. A. africanus ate a greater variety of foods that took a lesser toll on teeth, he adds.

A second investigation, led by evolutionary biologist Robin Crompton of the University of Liverpool in England, finds that Little Foot had humanlike hips and limb proportions, with longer legs than arms, indicative of upright walking. Those features are most comparable to a 3.6-million-year-old Australopithecus afarensis skeleton from East Africa dubbed Big Man, suggesting that the ability to walk upright evolved at the same time in different regions (SN: 7/17/10, p. 5).

Little Foot walked efficiently but remained a good tree climber, the researchers say. She would have moved across tree branches upright while lightly grabbing branches with her arms for support, much as orangutans do. Crompton views this form of upright movement through trees as an evolutionary precursor of full-time, two-legged walking (SN: 8/4/07, p. 72).

Paleoanthropologist Owen Lovejoy of Kent State University in Ohio, who led the analysis of Big Man’s skeleton, doubts that Little Foot did much walking across tree branches and rejects Crompton’s scenario of how upright gaits evolved. Big Man and Little Foot display bodies primarily suited for upright walking, he asserts.

Lovejoy says that one of the new papers supports his contention that tree climbing was far less important to Little Foot’s kind than walking on the ground was. As a child, Little Foot fell from a short height and suffered a bone-bending forearm injury, concludes a group that includes Clarke. That Little Foot survived into adulthood with an injury that the authors say impeded tree climbing underscores the prominence of upright walking in her species, whatever its official name, Lovejoy contends.

Independent studies of Little Foot’s body parts will help to resolve controversies about her evolutionary identity and way of life, predicts paleoanthropologist Carol Ward of the University of Missouri in Columbia. “This skeleton holds so much scientific potential.”

Citations

R.H. Crompton et al. Functional anatomy, biomechanical performance capabilities and potential niche of StW 573: an Australopithecus skeleton (circa 3.67 Ma) from Sterkfontein Member 2, and its significance for the last common ancestor of the African apes and for hominin origins. bioRxiv. Posted online November 29, 2018. doi:10.1101/481556.

L. Bruxelles et al. A multiscale stratigraphic investigation of the context of StW 573 Little Foot and Member 2, Sterkfontein Caves, South Africa. bioRxiv. Posted online November 29, 2018. doi:10.1101/482711.

R.J. Clarke and K. Kuman. The skull of StW 573, a 3.67 Ma Australopithecus skeleton from Sterkfontein Caves, South Africa. bioRxiv. Posted online December 4, 2018. doi:10.1101/483495.

A.J. Heile et al. Bilateral asymmetry of the forearm bones as possible evidence of antemortem trauma in the StW 573 Australopithecus skeleton from Sterkfontein Member 2 (South Africa). bioRxiv. Posted online December 5, 2018. doi:10.1101/486076.

L.R. Berger and J. Hawks. Australopithecus prometheus is a nomen nudum. American Journal of Physical Anthropology, in press, 2018.

Further Reading

B. Bower. Ardi walked the walk 4.4 million years ago. Science News Online, April 2, 2018.

B. Bower. ‘Little Foot’ pushes back age of earliest South African hominids. Science News. Vol. 187, May 2, 2015, p. 8.

B. Bower. Lucy fossil gets jolted upright by Big Man. Science News. Vol. 178, July 17, 2010, p. 5.

B. Bower. Red-ape stroll. Science News. Vol. 172, August 4, 2007, p. 72.

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