Ancient human relative, Australopithecus sediba, “walked like a human, but climbed like an ape.” New Fossils Improve Our Understanding of Bipedality and Being Human
Newly described fossils of A. sediba show that sediba was capable of walking equally as well arboreally as terrestrially! Join us as we take a deep dive into this new announcement from Dr. Lee Berger et al.
Sediba first emerged with then nine-year-old Matthew Berger’s finding of the Malapa hominins on August 15th, 2008. As we have seen so many times before with such discoveries, the paleoanthropological world would never be the same again! This new species would hold many secrets, and li ke other finds before it, answer many questions. The thing with science, and especially paleoanthropology, is that the more we find out, it seems the more questions we have! There is always more to learn!
So, who is Australopithecus sediba? Sediba was found in Malapa, Gauteng Province, South Africa in a cave that was blasted open by miners nearly a century ago. Professor Lee Berger, Matthew, and a few friends were exploring the local area with their dog. Berger looked at his son and told him, “Go find some fossils!”. Little did he know, and dare he not expect what was about to happen.
“Dad I found a fossil!” rang his son’s excited voice, and there, in a large rock that had been blown out of the cave, was a piece of hominin clavicle. Even from a distance Prof. Berger knew what this was, for he had done his dissertation on the very thing.
After excavation, examination and analysis, A. sediba was officially designated as a new species, and it was given a preliminary place on our family tree. Two partial skeletons were discovered: the holotype, MH1, a juvenile; and MH2, an adult female, newly dubbed “Issa,” which means ‘Protector’ in Swahili. Dating to 2 million years ago (MYA), these fossils did not seem to belong where they were found. These creatures seemed to be clearly adapted for a life in the trees, as shown by their upper and lower limb morphology. Examinations from Berger’s team tentatively assumed that sediba was an arboreal hominin, unlike some of its more well-known kin such as Lucy, (A. afarensis, 3.4 MYA).
One of the biggest questions in paleoanthropology is when did we become obligate (or full-time) bipeds? Bipedality is a universal feature of modern humans, and of hominins in general. It is one of the defining features. But we do not know exactly how bipedality came about.
In the history of the Earth, bipedality was nothing new. Dinosaurs and other early creatures experimented with it. Birds are bipedal. But no animal did what the ape lineage began to d o some tens of millions of years ago in the forest canopy. They developed long arms and legs and divergent big toes, and long, grasping fingers to hold onto branches securely as they moved through the trees.
The original sediba fossils from 2008 support the conclusion that like many arboreal primates, sediba could also move on the ground and probably even bipedally, but there was little direct evidence to show that they could walk for long lengths of time, as later hominins do.
But now we have these new sediba fossils – several contiguous bones of lower spinal vertebrae. These new fossils show us a view we have never had of an early hominin, a complete view of their lower spine.
These lumbar vertebrae show some very specific features that support the hypothesis that sediba was an obligate, or full-time, bipedal hominin, who by choice or necessity could also easily climb through the tree canopy.
These new fossils show that Au. Sediba had what is called a lumbar lordosis, or curvature of the spine—-think of the “S” shaped spine of modern humans. This S shape is only found in creatures that are fully bipedal, providing strong evidence of sediba’s ability to move easily on the ground.
If this hypothesis proves to be true, sediba could be an updated type of “missing link” — with features extremely primitive and ape-like, as well as features that are found in you and I!
Despite the features of the 2008 fossils have that showed that sediba was adapted for climbing and arboreal locomotion, these newly described 2015 fossils show that sediba had very modern traits as well, traits that allowed it to walk upright through the woodlands too. These new finds shed light on a part of our history that we have so many questions about. While we may now have some answers to our questions, there are of course more and more questions! Only the future, and continued analyses and study will reveal the many secrets that these hominins contain, as a glimpse into our very distant past. There is much work to do!
So what does this all mean? Well, Sediba was is a perfect example of mosaic evolution, some parts of the fossils are more modern, while other parts are more primitive. There is no one link, no one species that fills all the gaps, checks all the marks. But what we have learned about sediba, will lead to a better understanding of how we began to walk upright, when, and possibly even why.
Well, there you have it! If you would like to learn more about these new fossil finds, please refer to the official media release statement from Dr. Berger and Wits University, as well as the Q/A that they have provided!
“Ancient human relative, Australopithecus sediba, “walked like a human, but climbed like an ape”
New lower back fossils are the “missing link” that settles a decades old debate proving early hominins used their upper limbs to climb like apes, and their lower limbs to walk like humans
New York and Johannesburg – An international team of scientists from New York University, the Unive rsity of the Witwatersrand and 15 other institutions announced today in the open access journal e-Life, the discovery of two-million-year-old fossil vertebrae from an extinct species of ancient human relative.
The recovery of new lumbar vertebrae from the lower back of a single individual of the human relative, Australopithecus sediba, and portions of other vertebrae of the same female from Malapa, South Africa, together with previously discovered vertebrae, form one of the most complete lower backs ever discovered in the early hominid record and give insight into how this ancient human relative walked and climbed.
The fossils were discovered in 2015 during excavations of a mining trackway running next to the site of Malapa in the Cradle of Humankind World Heritage Site, just Northwest of Johannesburg South Africa.
Malapa is the site where, in 2008 Professor Lee Berger from the University of the Witwatersrand and his then nine-year old son, Matthew, discovered the first remains of what would be a new species of ancient human relative named Australopithecus sediba.
Fossils from the site have been dated to approximately two million years before present. The vertebrae described in the present study were recovered in a consolidated cement-like rock, known as breccia, in near articulation.
Rather than risking damaging the fossils, they were prepared virtually after scanning with a Micro-CT scanner at the University of the Witwatersrand, thus removing the risk of damaging the closely positioned, delicate bones during manual preparation. Once virtually prepared, the vertebrae were reunited with fossils recovered during earlier work at the site and found to articulate perfectly with the spine of the fossil skeleton, part of the original Type specimens of Australopithecus sediba first described in 2010. The skeleton’s catalogue number is MH 2, but the researchers have nicknamed the female skeleton “Issa,” meaning protector in Swahili. The discovery also established that like humans, sediba had only five lumbar vertebrae.
“The lumbar region is critical to understanding the nature of bipedalism in our earliest ancestors, and to understanding how well adapted they were to walking on two legs,” says Professor Scott Williams of New York University and Wits University and lead author on the paper.
“Associated series of lumbar vertebrae are extraordinarily rare in the hominin fossil record, with really only three comparable lower spines being known from the whole of the early African record.”
The discovery of the new specimens means that Issa now becomes one of only two early hominin skeletons to preserve both a relatively complete lower spine and dentition from the same individual, allowing certainty as to what species the spine belongs to.
“While Issa was already one of the most complete skeletons of an ancient hominin ever discovered, these vertebrae practically complete the lower back and make Issa’s lumbar region a contender for not only the best-preserved hominin lower back ever discovered, but also probably the best preserved,” says Berger, who is an author on the study and leader of the Malapa project. He adds that this combination of completeness and preservation gave the team an unprecedented look at the anatomy of the lower back of the species.
Previous studies of the incomplete lower spine by authors not involved in the present study hypothesized that sediba would have had a relatively straight spine, without the curvature, or lordosis, typically seen in modern humans. They further hypothesized Issa’s spine was more like that of the extinct species Neandertals and other more primitive species of ancient hominins older than two million years.
Lordosis is the inward curve of the lumbar spine and is typically used to demonstrate strong adaptations to bipedalism.
However, with the more complete spine, and excellent preservation of the fossils, the present study found the lordosis of sediba was in fact more extreme than any other australopithecines yet discovered, and the amount of curvature of the spine observed was only exceeded by that seen in the spine of the 1.6-million-year-old Turkana boy (Homo erectus) from Kenya, and some modern humans.
“While the presence of lordosis and other features of the spine represent clear adaptations to walking on two legs, there are other features, such as the large and upward oriented transverse processes, that suggest powerful trunk musculature, perhaps for arboreal behaviors,” says Professor Gabrielle Russo of Stony Brook University and an author on the study.
Strong upward oriented transverse spines are typically indicati ve of powerful trunk muscles, as observed in apes. Professor Shahed Nalla of the University of Johannesburg and Wits who is an expert on ribs and a researcher on the present study says: “When combined with other parts of torso anatomy, this indicates that sediba retained clear adaptations to climbing”.
Previous studies of this ancient species have highlighted the mixed adaptations across the skeleton in sediba that have indicated its transitional nature between walking like a human and climbing adaptations. These include features studied in the upper limbs, pelvis and lower limbs.
“The spine ties this all together,” says Professor Cody Prang of Texas A&M, who studies how ancient hominins walked and climbed. “In what manner these combinations of traits persisted in our ancient ancestors, including potential adaptations to both walking on the ground on two legs and climbing trees effectively, is perhaps one of the major outstanding questions in human origins.”
The study concludes that sediba is a transitional form of ancient human relative and its spine is clearly intermediate in shape between those of modern humans (and Neandertals) and great apes.
“Issa walked somewhat like a human but could climb like an ape,” says Berger.
Note: The virtual fossils published in the new study are free to download on Morphosource.org
Link to media pack:
For more information contact:
Professor Lee Berger (South Africa)
(+27) 83 454 6309
Professor Scott Williams (USA)
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Q/A Provided by Wits and Lee Berger et al.
Questions and answers about the lower back of Australopithecus sediba
Q: How were these new fossils discovered?
A: The block containing the fossils was removed from a trackway built by miners, who had a century ago blasted rock from what would later become known as the site of Malapa. The lumbar vertebrae discovered within the block were found to refit perfectly with previously known lower lumbar vertebrae of the MH2 skeleton.
Q: How do we know about the curvature of the lumbar spine and how does it relate to back problems in living people?
A: The upper and lower surfaces of the vertebral bodies are not parallel to each other. Instead, they form a wedge such that several lumbar vertebrae together create a curve, the lumbar lordosis (lumbar depression). This curve contributes to a balanced position of the center of body mass so that no force is needed to stand upright. If this balance is not achieved or if body mass compresses the lumbar spine too much, back pain can result.
Q: How do we know how many regional numbers of vertebrae a fossil hominin had?
A: Like us, all primates have multiple vertebral regions that serve different functions: cervical (neck) vertebrae, thoracic (rib-bearing) vertebrae, lumbar (lower back) vertebrae, sacral (pelvic) vertebrae, and coccygeal (tailbone) vertebrae. Most fossils are incomplete to various degrees. As far as completeness goes, the A. sediba partial skeletons are fairly complete. The adult female (MH2) now has a nearly complete lower back—all five lumbar vertebrae are represented, and we know that’s all there are because we also have the lower thoracic vertebrae and the sacrum, which surround the lumbar region.
Q: Might the curvature in MH2’s lower back be due to the fact that she was a female? Is it possible that male members of A. sediba didn’t have lumbar lordosis?
A: This is certainly a possibility. A. sediba falls nearest the modern human female mean, whereas a male A. africanus specimen, a close relative of A. sediba, falls near the modern human male mean. Modern humans are sexually dimorphic, where females demonstrated more lordosis on average than males, although significant overlap between the sexes exists. We might expect male A. sediba individuals to show less evidence for curvature than Issa (aka Malapa Hominin 2) and other females. There is a male partial skeleton (“Karabo,” Malapa Hominin 1), but it belongs to a juvenile individual currently known from just two lumbar vertebrae.
Q: What movements does one observe in the lumbar region?
A: The lumbar region allows flexion (forward bending) and extension (backward bending), with limited lateral bending. Rotation is restricted in the lumbar region, whereas it is achieved in the thoracic region. These movements are achieved (and prevented) largely by the orientation of the intervertebral articular facet joints, which are generally flat in thoracic vertebrae and curved in lumbar vertebrae.
Q: We know now that A. sediba had five lumbar vertebrae, just like humans. Why is that important to know?
A: Numbers of vertebrae above the pelvis (presacral vertebrae) are highly conserved in mammals (https://ecoevocommunity.nature.com/posts/48312-on-the-backs-of-mammals-evolutionary-constraint-in-the-evolution-of-the-mammalian-vertebral-column). Therefore, they are useful for figuring out how fossils are related to each other and to living species. As far as we know, all hominins have five lumbar vertebrae, but A. africanus, A. sediba, and Homo erectus differ from the average modern human in having a more mobile last thoracic vertebra, adding to the mobility of the lower back and potentially facilitating lordosis in these species.
Q: With its mosaic features, is A. sediba a “Missing Link”?
A: The term “Missing Link” is often used to speak about ancient human relatives. It derives from the idea that evolution is like a “chain” where one species inevitably “links” to the next more advanced. This is where the misleading image often seen on T-shirts of the “march of progress” from a primitive four-legged ancestor all the way to modern humans. Evolution doesn’t happen that way and the actual image of human evolution is more like a braided stream, with complex interactions occurring between species in the past through gene exchange. Some species go extinct, some share their genes with others, and some persist through long periods of time, but may make no contribution to future generations. Issa’s spine though is a sort of missing link between the upper body and lower body. Some scientists had long thought that australopithecines like A. sediba climbed well due the anatomy of their upper limbs. Other scientists disagreed seeing the adaptations in the lower limbs as committed to terrestrial bipedalism and early hominins would climb no better than a human and certainly not as well as an ape. As the spine “links” the lower body with the upper body, it shows us, in Issa, that she could and did climb using her upper limbs as well as many apes, but it also shows she could walk on two legs extremely well. So, the discovery of her spine was in some ways the “missing link” for proving that A. sediba could climb as well as an ape, but still walk on two legs efficiently.”
What an amazing announcement! We are so grateful to be a part of sharing this amazing news, and helping educate and share the information so that all can understand it! If you have any questions, please feel free to contact myself at firstname.lastname@example.org or any of the listed contacts above!
Now, before we go, let us give a quick thanks to all of the authors involved!
Well, and there you have it! What an exciting day! I thank you all for participating with us here, and I hope you have learned a great deal and are now up to date with some of the latest ideas and hypotheses!
Be sure to join us next time!
World of Paleoanthropology
You can find a link to the actual paper below, and in our Featured Papers section!