The study was led by researchers from the GREAB (UAB) in collaboration with the MECAMAT Research Group at the University of Vic – Central University of Catalonia (UVic-UCC). The team also included members from the University of Granada, the Archaeology Museum of Catalonia (MAC), the Camp de les Lloses Interpretation Center, the University of Lleida, and the TR2Lab Research Group at UVic-UCC.

The research team applied an innovative methodology based on the histological and elemental analysis (tissue and chemical composition) of deciduous, or baby, teeth found in the infants’ skeletons. Through optical microscopy, this approach allowed them to observe growth lines on the dental crown formed during intrauterine development and shortly after birth, identifying the neonatal line that appears at birth. This technique enabled the researchers to pinpoint the exact birth moment and postnatal survival of the infants, as well as to determine their precise chronological age at the time of death. Chronological age accounts for the time elapsed since birth rather than the biological development of the skeleton.

The Iberian culture inhabited the eastern and southern coastal regions of the Iberian Peninsula during the Iron Age (8th-1st centuries BCE). The most common funerary ritual among the Iberians was cremation, with remains placed in urns and buried in necropolises. However, archaeologists have also discovered burials containing uncremated remains of newborns located in areas designated for housing or production. These burials have sparked controversy among experts, who have proposed hypotheses suggesting these could represent deaths from natural causes, evidence of infanticide practices, or even ritual sacrifices.

Unique Technique for Pinpointing Birth and Death

The histological analysis applied by the researchers is an important innovation for precisely calculating the age at death by studying the dental crown. Deciduous (baby) teeth start forming during intrauterine life and complete their formation around birth, a period during which they record growth through the unique formation of growth lines. These lines can form daily but may also become thicker due to specific, stressful events. One of these distinctive lines, visible under optical microscopy in the teeth of infants who survived birth, is the neonatal line, which forms from the physiological stress of the transition from intrauterine to extrauterine life.

“The technique we have employed is unique because it allows us to identify the moment of birth and calculate chronological age in skeletal remains,” explains Ani Martirosyan, a predoctoral researcher at UAB and the study’s lead author. “Conventional techniques estimate biological age based on skeletal growth and development, resulting in high variability in age determination and making it impossible to pinpoint the exact moment of birth.”

This methodological innovation enabled the team to differentiate between infants who died at birth and those who survived. Among those who died at birth, they identified full-term (37-42 weeks of gestation) and preterm (before 37 weeks) individuals. They were also able to determine the exact chronological age of infants who survived beyond birth.

The researchers validated their technique using modern teeth samples with known chronological ages at death. Additionally, they used synchrotron-based X-ray microfluorescence at the ALBA Synchrotron in Cerdanyola del Vallès, specifically on the XALOC beamline, to analyze the elemental composition in the neonatal line. This included zinc quantification in cases where the histological visualization of the line was uncertain.

This study has been published in the Journal of Archaeological Science now provides strong evidence supporting the hypothesis that these infants buried in domestic contexts mainly died from natural causes and therefore reflect the high infant mortality rate during the first year of life in the period studied.

The authors reached this conclusion after examining 45 infant skeletons from five Iberian archaeological sites, including Camp de les Lloses (Osona), Olèrdola (Alt Penedès), Puig de Sant Andreu and Illa d’en Reixac (Baix Empordà), and the Fortress of Vilars d’Arbeca (Lleida).

https://doi.org/10.1016/j.jas.2024.106088