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µCT analysis determines survival time of Stone Age twins

(13.11.2020)

In 2005, archaeological excavations on the Wachtberg in Krems an der Donau (Austria) revealed two Upper Paleolithic infant burials. Among them was the 31,000 years old double burial of two infants, protected by the shoulder blade of a mammoth and well preserved. Genetic, morphological and chemical studies were able to identify the two infants as identical twins and shed light on their short survival time.

Few infant burials have survived from the time of the early anatomically modern human of the late Paleolithic, and so the discovery by the archaeologists from the Austrian Academy of Sciences is a global legacy of outstanding importance for answering developmental and evolutionary questions about our species. A team of 16 scientists from various disciplines and institutions – including LBI Trauma - worked on answering these questions.

Molecular geneticists from the University of Vienna, Harvard University and the University of Coimbra were able to decipher the relationship between the infants. They identified them as two male twins – providing genetically verified evidence for the earliest known twin birth.

The bioinformatician Patrick Heimel from LBI Trauma, together with anthropologist Stefan Tangl and imaging specialist Toni Dobsak from the University Clinic of Dentistry Vienna, worked on determining the twins’ survival time. Therefore, the upper lateral deciduous incisors were scanned via µCT, a high-resolution computer tomography. Initially only intended for measuring the geometry, the scientists made an unexpected discovery on the scans: they succeeded in making the neonatal line (NNL) visible. It can be seen as a dark line in the tooth enamel and separates the prenatal from the postnatally formed enamel. From this characteristic, and the degree of development of other parts of the body, the conclusion was formed that the twins were born fully developed and that their ages differed. On histological specimens, conclusions can be drawn about the survival time by measuring the postnatal formation of the tooth enamel above the neonatal line. It was found that one of the twins died at or shortly after birth, while the other infant survived the birth by 6-7 weeks.

These results are also supported by chemometric analyzes by isotope analysts and chemists at the Montan University in Leoben and the Pennsylvania State University. Barium, which due to the placental barrier does not enter the tooth enamel prenatally, is absorbed from breast milk and stored in the tooth enamel after birth. In the case of the buried twins, the presence of barium in the enamel shows that the infant who died prematurely had at least one attempt to breastfeed. In the postnatal enamel of the 6-7 week old baby, a larger increase in the barium signal was found.

The different times of death of the twins can also explain the different positions of the physical remains of the two infants. This indicates the reopening of the grave - a cultural and historical finding of great relevance, as it expands the previously known spectrum of burial practices of this age.

Only through the collaboration of scientists from different departments it was possible to expand the already sensational archaeological find by several small sensations. Both the DNA evidence of such an early twin birth and the different ages of death of the twins in the same grave are unique worldwide. The discovery of the “Wachtberg twins” is of outstanding importance for answering developmental and evolutionary questions about our species.