Ancient Teeth Reveal Real Causes of Infant Deaths in Iron Age Spain

A team of Spanish scientists has reached some important conclusions about the cause of death of newborn infants who passed away prematurely in large numbers on the Iberian Peninsula more than 2,000 years ago. According to researchers from the Autonomous University of Barcelona (UAB) and the University of Vic – Central University of Catalonia (UVic-UCC), these infants died of natural causes, such as labor-related complications or premature births, and not because they were murdered or sacrificed.

The infants in question belonged to what archaeologists refer to as the Iberian culture. The people of this culture lived in the eastern and southern coastal regions of the Iberian Peninsula during the Iron Age, which lasted from the eighth through the first centuries BC.

Unusual Infant Burials Spark Questions

The Iberians usually cremated their dead, storing the remains in urns that would be buried in a necropolis. Curiously, however, archaeologists have unearthed the burials of many Iberian newborns that were not cremated. Additionally, these tiny skeletons were not buried in regular cemeteries, but in areas where houses and production facilities were built.

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Burial of a perinatal individual from the Fortalesa dels Vilars (Arbeca, Lleida) site. (Credit: ARQHISTEC-GIP, UdL/Journal of Archaeological Science)

Because of the unusual nature of these findings, there has been debate about their significance and meaning. There have been suggestions that the newborns might have been victims of infanticide or used for sacrificial purposes, which might explain why they were buried in unconventional locations.

Given the great passage of time, researchers faced difficulties trying to find evidence that would solve this mystery. The newly completed study by the Spanish researchers has finally addressed this problem, in a highly innovative fashion.

Tiny Teeth Tell the Tale

To investigate the various possibilities, the UAB and Uvic-UCC researchers performed an extensive examination of the teeth of 45 infant skeletons excavated from Iron Age archaeological sites in Catalonia. They used advanced technology (optic microscopy and synchrotron light immersion) to carry out this study, in order to identify the precise moments when these infants were born and when they died.

In a new article published in the Journal of Archaeological Science, the researchers detailed the results of their study, which provided strong evidence that the children had all died of natural causes. There was a high rate of infant mortality in Iron Age Iberia, but one that was directly related to the normal risks of childbirth and not to intentional acts of violence committed for any reason.

Using optical microscopy, the researchers completed a thorough chemical and tissue analysis of the children’s primary teeth (the so-called milk teeth). They identified growth lines on the dental crowns of the teeth, including the neonatal line that is only produced at the moment of birth, and other lines produced as a newborn continues to develop. With this data they were able to determine whether or not a deceased newborn had been born alive, and if so how long before death occurred.

Neonatal line of a baby’s central incisor from the Olèrdola (Alt Penedès) site. (Biological Anthropology Unit, UAB/Journal of Archaeological Science)

What the Spanish researchers discovered was most enlightening. They found that nearly half of the infants had passed away during the perinatal period, or between the 27th week of gestation (40 weeks is the normal term) and the end of the first week of life outside the womb. Almost all of these babies died at the moment of birth, which was premature in many instances.

"These data reinforce the hypothesis that the majority of perinatal deaths were caused by natural factors, such as birth complications or health problems associated with prematurity, and not by cultural practices such as infanticide or ritual sacrifice, as some hypotheses have suggested," study co-author Xavier Jordana, an Associate Professor in the Department of Animal Biology, Plant Biology and Ecology at the Autonomous University of Barcelona, said in a UAB press release.

As for the remainder of the infants, the oldest of these lived for just 67 days.

"In the sites studied, no burial of an infant beyond two months of life has been identified,” said UAB researcher and study co-author Assumpció Malgosa. “This leads us to think that it could probably have been due to a cultural practice of burying in domestic spaces the infants who died in the earliest stages.”

High-Tech Analysis Confirms the Findings

The techniques used to obtain the data analyzed in this study represent an innovative method for learning more about the birth experiences of infants who died long ago. The researchers were able to use the neonatal line that forms on the dental crown at birth as a marker in time, because of the unusual circumstances under which it is created. It is a thicker line than others because of the stress involved in birth, which creates a physiological response that causes the thickening effect.

"The technique we used is unique, because it allows us to identify the moment of birth and calculate the chronological age in the skeletal remains.” said Ani Martirosyan, a predoctoral researcher at the UAB and the lead author of the Journal of Archaeological Science article.

Conventional techniques estimate the biological age of the individual based on skeletal growth and development, so they have a great variability when determining age, and do not allow us to identify the moment of birth."

To verify the results of the optical microscopy testing, the researchers used synchrotron light generated by the powerful equipment at the ALBA Synchrotron facility in Barcelona to determine the exact chemical composition of the post-neonatal tooth lines. With this highly sensitive form of analysis, they were able to confirm a change in the composition of the teeth following birth, which involved an increase in levels of zinc and a decrease in levels of calcium. This is a result of zinc being passed on to the child by the mother as a result of breastfeeding, and the presence of more zinc in this case was used to corroborate the researchers’ conclusions about how long the infants had lived.

A Trailblazing Methodology Offers Promise for the Future

The Spanish researchers were excited by the results they obtained during their research. They expressed hope that what they accomplished could be achieved by other scientists using the same technology.

"The data from our study provide much more detailed and concrete information than we have had so far to establish the pattern of infant mortality in Iberian populations, and help to unravel important aspects of their life history and cultural practices,” Dr. Jordana concluded. “We trust that the methodology we applied will serve to continue to unveil other mysteries yet to be discovered about ancient populations.”

Top image: Left: Burial of a perinatal individual from the Fortalesa dels Vilars (Arbeca, Lleida) site. Credit: ARQHISTEC-GIP, UdL.  Right: Neonatal line of a baby's central incisor from the Olèrdola (Alt Penedès) site. Credit: Biological Anthropology Unit, UAB/Journal of Archaeological Science

By Nathan Falde