- Biggest-ever study of the two million-year-old fossils found in South Africa
- Australopithecus sediba is thought to be the most direct ancestor of modern humans
- Was adapted for climbing trees but not for efficient walking or running
Researchers have revealed an unprecedented insight into Australopithecus sediba, a two million-year-old human ancestor.
The fossils, which were studied by scientists across the world, show a mixture of primitive features and of more advanced features typical of later human species.
They analysed bones of sediba discovered near Johannesburg in 2008 to find out how he walked, chewed and moved.
As a result, it is believed that this new species is currently the best candidate for a direct ancestor of our own species.
The human ancestor had a narrow upper rib cage which is similar to that of large apes, such as gorillas, but which is different to the human thorax which is uniformly cylindrical.
The researchers believe that it is the narrow upper thorax of apes that enables them to move their shoulder blades so that they can climb trees, however, it prevents them swinging their arms which makes walking upright much more difficult.
Therefore, Dr Peter Schmid, of the University of Zurich, assumes that Au. sediba was not able to walk or run on both feet as well as humans can.
‘They probably couldn't run over longer distances, especially as they were unable to swing their arms which saves energy,’ he said.
While the lower thorax was less well preserved, it appeared to show that the early human had a slim waist similar to that of a modern human.
An examination of the lower extremities also revealed a heel, metatarsus, knee, hips and back, which are unique and unprecedented.
It suggested that sediba walked with feet turned sharply inwards.
The teeth of this species were also studied and indicate that it is also a close relative of the previously identified Australopithecus africanus.
Both of these species are more closely related to humans than other australopiths from east Africa, according to the new research.
The study, published in the journal Science, also revealed that both africanus and sediba shared about the same number of dental traits with the first undeniably human species.
‘Our study provides further evidence that sediba is indeed a very close relative of early humans, but we can't definitively determine its position relative to africanus,’ said Dr Debbie Guatelli-Steinberg, co-author of the study and professor of anthropology at The Ohio State University.
The researchers examined the teeth from sediba and compared them to eight other African hominin species, which include modern humans from Africa, and extinct species of Homo, Australopithecus, and Paranthropus.
In all, the researchers examined more than 340 fossils and 4,571 recent specimens.
They also examined teeth from 44 gorillas for comparison.
The focus was on 22 separate traits of tooth crowns and roots that can give clues as to the relationship between the different species studied.
Researchers use standardised measurements from the Arizona State University Dental Anthropology System to compare the teeth on these 22 traits.
The researchers found that on 15 of these traits, sediba and africanus scored the same. Sediba shared 13 traits with Homo erectus, an early human species, which was comparable to how africanus scored.
Sediba and africanus shared five dental traits that were not found in earlier australopiths, further showing their close relationship. Both also share five traits with early humans – Homo habilis/rudolfenis and Homo erectus -- which were not shared with earlier ancestors, demonstrating the close relationship between these two australopiths and the first humans.
Dr Guatelli-Steinberg said their dental analysis showed that both africanus and sediba are more closely related to humans than the famous ‘Lucy’ skeleton fossil found in East Africa in 1974. This fossil represented a species, Australopithecus afarensis, that was at one time was thought to be the closest relative of humans.
Lucy is estimated to have lived 3.2 million years ago. Sediba lived 1.977 million years ago, while africanus lived between 3.03 and 2.04 million years ago.
‘Our research on teeth can't definitively settle if either sediba or africanus is more closely related to humans than the other species,’ Dr Guatelli-Steinberg said.
‘But our findings do suggest that both are closely related to each other and are more closely related to humans than afarensis.
‘We need to find more sediba remains to help fill in the missing pieces of this evolutionary puzzle.’
An analysis of the cervical, thoracic, lumbar and sacral region of the spinal column was also carried out and shows that Au. sediba had the same number of lumbar vertebrae as modern man.
The strong hollow back suggests that he was more advanced in this area than Au. africanus and may be more likely compared with Homo erectus.
Au. sediba had a human-like curvature of the lower back, but it was functionally longer and more flexible than that of modern humans.
‘They probably walked in a way that we might find strange—a ‘compromise’ form of bipedalism indicative of a hominin that still partially relied on climbing trees,’ Dr Scott Williams explained.
He noted that ‘the adult female is the first early hominin skeleton that preserves an intact terminal thoracic region and this provides critical information on the transition in inter-vertebral joints, and, by inference, mobility of the lower back.’
‘The bony spine of Au. sediba likely had the same number of vertebrae as that of modern humans,’ Dr Williams added.
‘However, it differed in one primary aspect of its configuration—the transition in inter-vertebral articular facets occurred at a higher level of the spine that than normally occurs in modern humans. In combination with other features, a functionally longer lower back would have allowed for a more flexible spine in Au. sediba relative to that of modern humans.’
In addition, morphological indicators of strong lumbar curvature suggest that Au. sediba evolved in this regard relative to Au. africanus, which lived between 3.03 and 2.04 million years ago, and closer to the more recent Nariokotome Homo erectus skeleton—to date, the most complete early human skeleton discovered.
The new study shows an image of a human species with a mosaic-like physique.
Some body parts are similar to those of earlier and others to those of later hominins.
‘The numerous similarities with Homo erectus suggest that Au. sediba represents the most appropriate early form of the genus Homo,’ said Dr Schmid.
He added: ‘The previous candidates are too fragmentary to be capable of occupying this position.’
Source: http://www.dailymail.co.uk/sciencetech/article-2307945/Pigeon-toed-unable-run-Researchers-shed-new-light-early-humans.html
0 comments
Posts a comment