Advertisement

The Mosaic Pre-Man

Newly excavated Australopithecus sediba fossils exhibit a mixture of primitive and more modern features.

By | September 8, 2011

The cranium of the juvenile skeleton of Australopithecus sedibaPICTURE BY: BRETT ELOFF. COURTESY OF LEE BERGER AND THE UNIVERSITY OF WITWATERSRAND

Australopithecus sediba fossils dating back nearly 2 million years ago may call for a shift in thinking about the origin of man. Excavated from the Malapa caves near Johannesburg, South Africa, the fossils—including a hand, foot and ankle, a pelvis, and a partial skull—are dated and described in five papers published online today in Science (September 8).  The combined findings indicate that Au. sediba had a mosaic of features, some primitive and distinctly of the genus Australopithecus, while others resembled those of Homo.

“If we found [the specimens] as separate parts, we’d probably think they came from different species or maybe even different genera of early human,” said Steven Churchill, an evolutionary anthropologist at Duke University and a co-author on four of the five papers.

The fossils, found in a layer of sediment that dated to 1.98 million years ago, suggest that Au. sediba may have more features in common with modern Homo than Homo habilis or Homo rudolfensis, prompting researcher to rethink the evolutionary relationships among ancient hominins, including the first members of the Homo genus. “The fossil record of early Homo is a mess,” Churchill said. “Sediba provides an opportunity for us to step back and say ok, what do we really know?”

Brain

Virtual endocast (green) of a juvenile male Australopithecus sediba. Yellow indicates portions of the skull that were reconstructed by mirror-imaging the anatomy on the opposite side.
Virtual endocast (green) of a juvenile male Australopithecus sediba. Yellow indicates portions of the skull that were reconstructed by mirror-imaging the anatomy on the opposite side.
PICTURE BY: ESRF/KJ CARLSON. COURTESY OF LEE BERGER AND THE UNIVERSITY OF WITWATERSRAND

Among the fossils found in the Malapa caves was a remarkably well-preserved skull of an adolescent Au. sediba boy. Although much of back portion of the skull was missing, the area encasing the front of the brain—the seat of abstract thought that is so well-developed in modern humans—was intact. Brain tissue does not fossilize, but its whorls and folds leave impressions on the inner surface of the skull bones, providing clues about a brain’s complexity, as well as its size.

“We can compare patterns in the arrangement of the brain’s bumps and valleys,” in order to place it in evolutionary context, said Kristian Carlson, the anthropologist at University of the Witwatersrand who led the team investigating the brain. To do this, the team produced a digital endocast, recreating the brain imprint left on the Au. sediba boy’s skull using X-ray scans.

Previous work suggested that increasing size and complexity occurred simultaneously, and gradually. But there’s a gap between fossils of the larger-skulled Homo erectus, dating to less than 2 million years ago, and Australopithecus skulls, mostly older than 2.3 million years, which are smaller in size and more chimpanzee-like in design. This interval is littered with contentiously dated fossil fragments that fail to clarify Homo’s origins, said Carlson. Au. sediba’s skull, dated right in the middle at 1.98 million years old, was “surprisingly small,” though already showing signs of reorganization, he said. The structural differences between the newly discovered brain impression and two endocasts of A. africanus (another Homo predecessor), such as the partial projection of the frontal lobe, “foreshadow” characteristics of Homo skulls, and nominate Au. sediba as a transitional species preceding H. erectus, explained Darryl J. de Ruiter, a paleoanthropologist at Texas A&M University, who participated in the skull’s analysis.

Not everyone agrees that Au. sediba was quite so advanced, however. Dean Falk, a paleoanthropologist at the School for Advanced Research in Santa Fe, New Mexico, and at Florida State University, who was not involved in the research, said Au. sediba is an “exciting” find, but she is not convinced that its brain is any closer to human than Au. africanus’s brain is. It’s certainly possible, she said, but more comparisons are necessary to establish that Au. sediba is indeed a transition to Homo.

--Sabrina Richards

Hands & Feet

The right hand skeleton of an adult female Australopithecus sediba against a modern human hand
The right hand skeleton of an adult female Australopithecus sediba against a modern human hand
PICTURE BY: PETER SCHMIDT. COURTESY OF LEE BERGER AND THE UNIVERSITY OF WITWATERSRAND

Like the fossilized skull, the hands and feet of the Au. sediba specimens showed a surprising combination of both modern and primitive features, according to the authors. A well-preserved partial foot and ankle hints at a unique form of bipedalism—one of the most critically defining characteristics of the Homo genus—combined with some degree of aboreality.

Furthermore, the nearly complete hand and wrist set recovered from an adult Au. sediba female appears “hyper human,” Churchill said.  Its thumb is relatively longer, as compared to the appendages of modern Homo sapiens, which themselves have proportionally longer thumbs than chimpanzees.  Like humans, this would allow Au. sediba to exert pressure when manipulating objects.

The orientation of the wrist bone and joints also suggest a structure that is “good at withstanding the forces you get when you’re knocking rocks together,” Churchill said. The researchers think that Au. sediba not only used stone tools, but perhaps made them, too. “We’ve found tools at the site,” Churchill said, “but we haven’t found any tools in situ so we can’t say for sure.”

Other hominins, like Homo habilis, also evolved anatomical structures for tool usage, but not in the same ways. H. habilis had a mobile thumb and robust, curved finger bones, for example, but lacked Au. sediba’s well-developed muscle structure. This suggests that parallel but different tool-oriented morphologies arose in the same period, Churchill said, meaning researchers may need to reevaluate expectations of what the tool-using hand looked like in this early time window.

--Rachel Nuwer

Pelvis

Pelvis of Australopithecus sediba
Pelvis of Australopithecus sediba
PICTURE BY: PETER SCHMIDT. COURTESY OF LEE BERGER AND THE UNIVERSITY OF WITWATERSRAND

Analysis of the partial adult female Au. sediba pelvis also revealed features that closely resemble the broader pelvises of modern humans. Anthropologists typically attribute the broadening of the pelvis early in hominin evolution to the advent of bipedal locomotion, Churchill said, with further growth later in evolution to allow for the birthing of babies with larger skulls.  Au. sediba, however, is a small-brained hominin, suggesting that the species' broad pelvis is purely a result of a change in the biomechanical forces. Researchers speculate that Au. sediba’s formerly tree-dominated landscape started shifting towards savannah around this time, allowing Au. sediba to expand its range. The increased walking would have created a selection pressure on the pelvis for more efficient bipedal locomotion.

Researchers like Scott Simpson, an anatomist at Case Western Reserve University who was not involved in the study, agree that the fossils are “extraordinary pieces” that will bear on our understanding of ancient human variation, but called for a direct comparison between the Au. sediba pelvis and those of early Pleistocene Homo specimens. “My concern is that [the researchers] have perhaps set the model as an either/or explanation, locomotion or obstetrics,” Simpson said. Because only a handful of specimens have ever been recovered, he said, researchers’ understanding of ancient pelvic anatomy contains many gaps. Therefore, the specimens “absolutely, positively require a very thorough and careful analysis.”

Still, a great fossil like Au. sediba is one that does not meet preconceptions. “Paleontologists are used to being fed scraps of fossils,” Simpson said. “It’s like a feast getting a skeleton of this magnitude. After a lifetime of crumbs, it’s a welcome meal.”

--Rachel Nuwer

K.J. Carlson, et al., "The endocast of MH 1, Australopithecus sediba," Science, 333:1402-07, 2011.

J.M. Kibii, et al., "A partial pelvis of Australopithecus sediba," Science, 333:1407-11, 2011.

T.L. Kivell, et al., "Australopithecus sediba hand demonstrates mosaic evolution of locomotor and manipulative abilities," Science, 333:1411-17, 2011.

B. Zipfel, et al., “The foot and ankle of Australopithecus sediba," Science, 333:1417-20, 2011.

R. Pickering, et al., “Australopithecus sediba at 1.977 Ma and implications for the origins of the genus Homo," Science, 333:1421-23, 2011.

Advertisement

Add a Comment

Avatar of: You

You

Processing...
Processing...

Sign In with your LabX Media Group Passport to leave a comment

Not a member? Register Now!

LabX Media Group Passport Logo

Comments

Avatar of: Minuet

Anonymous

September 9, 2011

I have not read a great deal on the subject of physical anthropology since my degree in the mid '70's. This article has re-ignited my fascination with the topic. Can anyone suggest some suitable books or journal articles to bring me up to speed?

Avatar of: DJ@HGEN

Anonymous

September 9, 2011

I can see this is very interesting and merits publication in Science. But why as five separate papaers in the same issue of Science? What happened to supplementary material? I am involved in editorial roles in a few journals and we are desparate to clamp down on salami slicing of research results. Dealing with each body part in its own manuscript seems a bit OTT. But then again, it's probably sour grapes as those of us who do research to try and feed the planet can only dream of gettting a single paper in Science, never mind five papers in a single issue...

Avatar of:

Posts: 0

September 9, 2011

I have not read a great deal on the subject of physical anthropology since my degree in the mid '70's. This article has re-ignited my fascination with the topic. Can anyone suggest some suitable books or journal articles to bring me up to speed?

Avatar of:

Posts: 0

September 9, 2011

I can see this is very interesting and merits publication in Science. But why as five separate papaers in the same issue of Science? What happened to supplementary material? I am involved in editorial roles in a few journals and we are desparate to clamp down on salami slicing of research results. Dealing with each body part in its own manuscript seems a bit OTT. But then again, it's probably sour grapes as those of us who do research to try and feed the planet can only dream of gettting a single paper in Science, never mind five papers in a single issue...

Avatar of:

Posts: 0

September 9, 2011

I have not read a great deal on the subject of physical anthropology since my degree in the mid '70's. This article has re-ignited my fascination with the topic. Can anyone suggest some suitable books or journal articles to bring me up to speed?

Avatar of:

Posts: 0

September 9, 2011

I can see this is very interesting and merits publication in Science. But why as five separate papaers in the same issue of Science? What happened to supplementary material? I am involved in editorial roles in a few journals and we are desparate to clamp down on salami slicing of research results. Dealing with each body part in its own manuscript seems a bit OTT. But then again, it's probably sour grapes as those of us who do research to try and feed the planet can only dream of gettting a single paper in Science, never mind five papers in a single issue...

Avatar of:

Posts: 0

September 22, 2011

More seeking, more discovery, more knowledge, more understanding.

Who are we? Where did we come from? Where are we going?

Avatar of:

Posts: 0

September 22, 2011

More seeking, more discovery, more knowledge, more understanding.

Who are we? Where did we come from? Where are we going?

Avatar of: EARTHMAN1

EARTHMAN1

Posts: 10

September 22, 2011

More seeking, more discovery, more knowledge, more understanding.

Who are we? Where did we come from? Where are we going?

Avatar of: JHolland

Anonymous

September 30, 2011

Thank you for the article.  Now I know that I am married to a bonobos act alike.

Avatar of:

Posts: 0

September 30, 2011

Thank you for the article.  Now I know that I am married to a bonobos act alike.

Avatar of:

Posts: 0

September 30, 2011

Thank you for the article.  Now I know that I am married to a bonobos act alike.

Avatar of:

Posts: 0

October 31, 2011

Very interesting and compelling research, but I wonder whether grouped with all the other A. africanus dat available, without the assumed specific designations, allows a more realistic sense of the species is arrived at. Classic (and typolgical) I would A. africanus can also be seen as a fairly variable species exisiting over a substantial length of time and geography. The presence of tools is suggestive, and one assumes the authors mean stone tools, but are there bone tools as well--shades of Raymond Dart's osteodontokeratic culture? I suspect that a new generation of paleoanthropologists will spend much time "clumping" what the "splitters" have created once a broader look at "australopithecines" is accomplished.

Avatar of:

Posts: 0

October 31, 2011

Very interesting and compelling research, but I wonder whether grouped with all the other A. africanus dat available, without the assumed specific designations, allows a more realistic sense of the species is arrived at. Classic (and typolgical) I would A. africanus can also be seen as a fairly variable species exisiting over a substantial length of time and geography. The presence of tools is suggestive, and one assumes the authors mean stone tools, but are there bone tools as well--shades of Raymond Dart's osteodontokeratic culture? I suspect that a new generation of paleoanthropologists will spend much time "clumping" what the "splitters" have created once a broader look at "australopithecines" is accomplished.

Avatar of: Donald L. Wolberg

Donald L. Wolberg

Posts: 18

October 31, 2011

Very interesting and compelling research, but I wonder whether grouped with all the other A. africanus dat available, without the assumed specific designations, allows a more realistic sense of the species is arrived at. Classic (and typolgical) I would A. africanus can also be seen as a fairly variable species exisiting over a substantial length of time and geography. The presence of tools is suggestive, and one assumes the authors mean stone tools, but are there bone tools as well--shades of Raymond Dart's osteodontokeratic culture? I suspect that a new generation of paleoanthropologists will spend much time "clumping" what the "splitters" have created once a broader look at "australopithecines" is accomplished.

Follow The Scientist

icon-facebook icon-linkedin icon-twitter icon-vimeo icon-youtube
Advertisement

Stay Connected with The Scientist

  • icon-facebook The Scientist Magazine
  • icon-facebook The Scientist Careers
  • icon-facebook Neuroscience Research Techniques
  • icon-facebook Genetic Research Techniques
  • icon-facebook Cell Culture Techniques
  • icon-facebook Microbiology and Immunology
  • icon-facebook Cancer Research and Technology
  • icon-facebook Stem Cell and Regenerative Science
Advertisement
Advertisement
Mettler Toledo
BD Biosciences
BD Biosciences