Xiahe lower jaw

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Xiahe lower jaw

Xiahe mandible is the name of a fossil that was discovered in the northeastern highlands of Tibet and that has been calculated to be approximately 160,000 years old. In a study published in the journal Nature in 2019 , it was announced that the lower jaw (named here as Xiahe mandible ) is attributed to the Denisova people . This fossil sites was also the first evidence the Denisova people outside of the Altai Mountains in Siberia located Denisova Cave and the oldest known evidence of the presence of a representative of Hominini in the highlands of Tibet.

The Xiahe mandible was named after its place of discovery in the Baishiya Cave , a paleoanthropological and archaeological archaeological site in the district of Xiahe of Autonomous Prefecture of Gannan Tibetan , People's Republic of China .

discovery

The Xiahe mandible was discovered and in 1980 by an unknown monk, located within 3280 meters Baishiya Cave of Jigme Tenpe Wangchug , 6 Gungthang Rinpoche of the monastery Labrang been passed, the it to the scientists of the Lanzhou University in Lanzhou passed on . The cave is a place of prayer of Tibetan Buddhism and has long been known as a depository of " dragon bones ", which are ground up by the local population and used as traditional Tibetan medicine . Presumably because the fossil resembles the lower jaw of a modern human, it was spared this use.

Dating

Using several samples from different areas of the lime crusts adhering to the lower jaw, it was possible to determine the age of these crusts with the help of uranium-thorium dating : according to this, the outer lime crusts are 155,000 ± 15,000 years old, the inner ones an age of 163,000 Calculated ± 10,000 years. From this it can be deduced that the lower jaw is approximately 160,000 years old and thus comes from the Middle Pleistocene .

Protein analysis

In July 2016, researchers from Lanzhou University contacted Jean-Jacques Hublin from the Max Planck Institute for Evolutionary Anthropology to jointly examine the Xiahe lower jaw for possible remains of fossil DNA (aDNA). It was not possible to extract aDNA samples in the following years, but residues of proteins could be obtained from dentin . In the absence of aDNA, thanks to the methods of paleoproteomics from the structure of proteins (from their amino acid sequence ), conclusions can be drawn about the genes that code them, so that a comparison with aDNA obtained elsewhere is still possible via this detour. According to the researchers, although the extracted proteins were severely degraded , they were clearly distinguishable from possible contamination by modern proteins.

A phylogenetic analysis of the obtained proteome revealed “a phylogenetic tree which exactly reflected the phylogenetic development of the great apes, including the relationship of Homo sapiens , Neanderthals and Denisovans. Within this system of relationships, the Xiahe proteome is closest to that of the Denisova humans. ”The analysis of single nucleotide polymorphisms came to the same conclusion . The Max Planck Society summarized the results of the investigations in 2019 as follows: "Our protein analysis showed that the Xiahe lower jaw belonged to a population that was closely related to the Denisova people from the Denisova Cave ." mentioned in the study that so far only a single genome of the Denisova people has been deciphered, that of the finds from the Denisova cave, which is why the genetic variation between the Denisova populations is so far unknown.

Other features

The Xiahe lower jaw shows morphological features that are typical of archaic hominine fossils from the Middle Pleistocene, for example Homo heidelbergensis , the ancestor of the Neanderthals: the jawbone is relatively thick and therefore very robust and becomes flatter towards the rear compared to the front . Two very large molars M1 and M2, as well as fragments of six front teeth without crowns (two premolars , one canine , three incisors ) have been preserved very well . It was emphasized that the lower jaw of Homo erectus - distinguish lower jaws, but similarities with the Xujiayao- and Xuchang -Fossilien and in particular with the Fossil Penghu one of the Penghu Islands ( Taiwan exhibiting).

Due to the special features of the preserved molars and their roots, which differ from those found in Neanderthals and archaic Homo sapiens , the Chinese researchers hope to be able to identify further specimens from the archived hominine fossils that can be assigned to the Denisova people .

A special feature of the dentition gave rise to speculations about the genetic proximity of the Denisova people to today's Asians, which is also proven in the fossil Penghu 1 , because the molar M2 has three roots. The molar M2 has three roots in less than 3.5 percent of all people outside of Asia, but more than 40 percent of the population in China has it; the rest of the people have only two M2 roots. The current state of research was that the three roots had only established themselves in the populations that had emigrated from Africa to Asia. A study published in July 2019, on the other hand, did not rule out that the triple roots could have come from the Denisova people to the Asian Homo sapiens through introgression . However, this assumption is controversial.

Web links

Individual evidence

  1. ↑ a b c Fahu Chen et al .: A late Middle Pleistocene Denisovan mandible from the Tibetan Plateau. In: Nature. Volume 569, 2019, pp. 409-412, doi: 10.1038 / s41586-019-1139-x
  2. ↑ Site plan of the site in the highlands of Tibet.
  3. ^ A b Jean-Jacques Hublin: How We Found an Elusive Hominin in China. On: sapiens.org from May 1, 2019
  4. ↑ Denisovans were the first human form in the highlands of Tibet. On: mpg.de from May 1, 2019
  5. ↑ Digital reconstruction: the lower Tibetan jaw freed from adhering calcareous crusts. On: nature.com from May 1, 2019.
  6. ↑ Ann Gibbons: First fossil jaw of Denisovans finally puts a face on elusive human relatives. On: sciencemag.org from May 1, 2019
  7. ^ Shara E. Bailey, Jean-Jacques Hublin, and Susan C. Antón: Rare dental trait provides morphological evidence of archaic introgression in Asian fossil record. In: PNAS . Volume 116, No. 30, 2019, pp. 14806–14807, doi: 10.1073 / pnas.1907557116 .
  8. ↑ G. Richard Scott, Joel D. Irish and María Martinón-Torres: A more comprehensive view of the Denisovan 3-rooted lower second molar from Xiahe. In: PNAS. Advance online publication of December 17, 2019, doi: 10.1073 / pnas.1918004116 .
    Shara E. Bailey, Kornelius Kupczik, Jean-Jacques Hublin and Susan C. Antón: Reply to Scott et al: A closer look at the 3-rooted lower second molar of an archaic human from Xiahe. In: PNAS. Advance online publication of December 17, 2019,     doi: 10.1073 / pnas.1918959116 .