DIK 1-1

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"Selam" or DIK 1-1

DIK1-1 is the scientific name for the fossil skeleton of a juvenile, female Australopithecus afarensis , which, due to its exceptionally good state of preservation, provides far-reaching insights into the behavior of this early pre- human species. It is by its discoverer also Selam ( peace called) and in English-speaking area after the site Dikika in Ethiopia as Dikika Girl or Dikika baby ( girl from Dikika ), respectively. Well-preserved children's skeletons were previously known only from the Neanderthal find from the cave of Dederiyeh ( Syria ) , apart from the skull of the child from Taung (an Australopithecus africanus ) and some partially deformed fragments .

The discovery

Reference of the Australopithecus afarensis

On December 10, 2000, Zeresenay Alemseged (then a postdoc at Arizona State University ) and his companion Tilahun Gebreselassie from the Ethiopian Antiquities Authority in the Dikika region (northeastern Ethiopia ) recovered the first skull fragments of the well-preserved, approximately three-year-old female individual, whose age is due the soil quality is given as 3.3 million years. DIK1-1 is thus about 150,000 years older than the famous Lucy , whose final resting place was only about 10 km north on the other side of the Awash River . In the excavation periods of 2002 and 2003, the skeleton was continuously completed by additional bone finds. In this way, the entire skull, completely dentate except for two teeth, including fossilized inner impressions, could be reconstructed, so that statements about the surface of the brain can also be made. The hyoid bone was found as well as both shoulder blades , large parts of the upper spine in the area of ​​the chest, all ribs , parts of an arm including a finger, both kneecaps , large pieces of the shins and a complete foot . It is therefore considered to be the most complete fossil of the Australopithecus afarensis species to date .

The discovery of the research group around Zeresenay Alemseged from the Max Planck Institute for Evolutionary Anthropology in Leipzig was first published in September 2006.

The analysis

Attempt at a reconstruction

From the find situation, the researchers conclude that the child was washed away by water immediately after its death, shortly afterwards buried under sand and possibly died by drowning. His remains were embedded in a cement-like sandstone block and thus remained fixed in place. The grains of sand were removed individually by the discoverer with dental tools in a five-year, several thousand hours of patient work.

The skull has a volume of approximately 275 to 330 cm³ and in this respect resembles that of a three-year-old chimpanzee . One difference to the chimpanzee skull is that at the age of three it is already 90 percent the size of an adult; DIK1-1, on the other hand, only owns between 65 and 88 percent of a fully grown Australopithecus skull and is therefore closer to modern humans than to modern great apes in this respect. According to the researchers, the volume of the skull when fully grown would have been 375 to 435 cm³.

In order to determine the age of the child when it died, the condition of its second teeth, some of which had not yet erupted, was compared with the teeth of young chimpanzees and young human children. However, since the speed of development of young australopithecins is still little known, the age calculated in this way - three years - is at best an approximate estimate, according to Bernard Wood . The sex of the child was also determined by comparing its crowns with the teeth of adult australopithecins.

The researchers hope to draw conclusions about the articulation ability of Australopithecus from the hyoid bone , which has only survived extremely rarely in human-like fossils (except for the Dikika find only in a single Neanderthal ) . According to an initial analysis, it resembles the hyoid bone of gorillas and not that of humans.

It is true that the pelvis and parts of the lower back and legs are missing in the "Dikika girl", which the online edition of the journal Nature referred to as Lucy's baby . However, the Leipzig researchers were able to examine the shoulder, hand and semicircular canals of the inner ear for the first time in a not yet fully grown Australopithecus. H. Body parts that can provide immediate information about body movements.

The large occipital opening , through which the rearmost part of the brain extends to the beginning of the spinal cord , is arranged much more strongly below the skull than in three-year-old monkeys, ie below the center of gravity . The thoracic spine consists - as with most of the later hominini - of 12 vertebrae and not, as in most chimpanzees, of 13 vertebrae.

The remaining foot and leg bones also confirmed beyond any doubt that a young Australopithecus could also walk on two legs , i.e. upright. However, the very well preserved right shoulder blade is more similar to that of a gorilla than that of a modern person and indicates that DIK 1-1 still often wandered with arms stretched up over the head. The semicircular canals of the inner ear are similar to those of chimpanzees , and even the only surviving finger has elongated and curved bones, as known from the chimpanzee. This curvature becomes more pronounced in young animals as they use their fingers to hold onto branches while climbing. The researchers interpret these findings as an expression of the fact that the "child of Dikika" could walk upright, but just as easily and often could hold his arms over his head, i.e. shimmy around in trees. However, the attachment surfaces of certain muscle groups seem to be less pronounced than in the great apes living today, so that a tree-dwelling way of life need not have been predominant. However, the authors of the study expressly point out that the connection between body structure and behavior in the great apes has hardly been researched and that one should therefore be cautious about the interpretation of fossil finds.

The discovery is also significant in that it is now possible to use the child's skeleton to understand the physical development of australopithecins from adolescent to adult and how quickly this development progressed in them. For example, the researchers hope that the analysis of the big toe, which is still hidden in the sandstone, will provide information on whether it was still designed as a gripping toe, i.e. whether the child could cling to the mother's fur with hands and feet. If this was no longer the case with Australopithecus afarensis , far-reaching conclusions about their social structure could be drawn from this finding.

literature

  • Christopher P. Sloan: Is this "Lucy's" child? In: National Geographic (German edition), December 2006, pp. 154–165
  • Kate Wong: Lucy's baby. In: Spectrum of Science. February 2007, pp. 32-39

Web links

Individual evidence

  1. ^ Zeresenay Alemseged et al .: A juvenile early hominin skeleton from Dikika, Ethiopia. In: Nature . Volume 443, 2006, pp. 296-301, doi: 10.1038 / nature05047
  2. ↑ to informed guess wrote the anthropologist Bernard Wood ( George Washington University , Washington ) in an article about "A precious little bundle". In: Nature. Volume 443, 2006, p. 278 f. doi: 10.1038 / 443278a
  3. ^ B. Arensburg et al .: A middle palaeolithic human hyoid bone. In: Nature. Volume 338, 1989, pp. 758-760, doi: 10.1038 / 338758a0
  4. ↑ Carol V. Warda et al .: Thoracic vertebral count and thoracolumbar transition in Australopithecus afarensis. In: PNAS. Volume 114, No. 23, 2017, pp. 6000–6004, doi: 10.1073 / pnas.1702229114
  5. ↑ David J. Green and Zeresenay Alemseged: Australopithecus afarensis Scapular Ontogeny, Function, and the Role of Climbing in Human Evolution. In: Science . Volume 338, No. 6106, 2012, pp. 514-517, doi: 10.1126 / science.1227123
  6. ↑ Jeremy M. DeSilva, Corey M. Gill, Thomas C. Prang, Miriam A. Bredella and Zeresenay Alemseged: A nearly complete foot from Dikika, Ethiopia and its implications for the ontogeny and function of Australopithecus afarensis. In: Science Advances. Volume 4, No. 7, 2018, eaar7723, doi: 10.1126 / sciadv.aar7723
  7. ↑ Christopher P. Sloan: Is this 'Lucy's' child? In: National Geographic (German edition). December 2006, p. 162.