On 16.07.2025, Ani Martyrosian Defends Doctoral Thesis at UAB: Enamel growth lines in deciduous teeth: Life history reconstruction in ancient populations, co-directed by Xavier Jordana (UAB/UVIC TR2Lab), Assumpta Malgosa (UAB), and Judit Molera (UVic Mecamat). She receives the Highest Distinction: Excellent Cum Laude.

Deciduous tooth enamel preserves biological events from prenatal and early postnatal life, offering a valuable archive for reconstructing life histories in ancient populations. This dissertation investigates enamel growth lines and trace element distributions in human deciduous teeth to refine age estimation methods and improve our understanding of infant mortality patterns in archaeological contexts. The central hypothesis posits that combining dental histology with trace element analysis enhances the precision of identifying the birth event via the Neonatal Line (NNL), even in archaeologically altered samples. The research objectives were to assess the accuracy of histological age estimation methods, reconstruct infant mortality patterns in ancient populations, validate synchrotron micro X-ray fluorescence (SR-µXRF) for NNL identification, and examine trace element preservation in archaeological enamel.

The study analyzed 68 deciduous teeth from modern (Granada osteological collection) and archaeological contexts (Iron Age and medieval sites). Each tooth was sectioned and examined under polarized and transmitted light microscopy to identify growth markers and calculate crown formation timing. Prenatal crown formation time (pCFT), corresponding to the interval from the start of enamel formation to birth, was compared with established ranges to confirm NNL presence. Additionally, 18 teeth were selected for SR-µXRF trace element analysis at ALBA and ESRF synchrotron facilities. Histological analysis demonstrated high accuracy in age estimation when tested against modern samples, confirming its applicability to archaeological contexts. In all modern individuals who survived birth, the NNL was present, and pCFT values fell within expected full-term birth ranges, reinforcing the NNL’s validity as a live birth marker. Age estimates closely matched recorded ages in individuals with still-forming enamel, with minor underestimations (≤2 days). For those with completed crowns, postnatal CFT underestimated survival time, revealing limitations of enamel-based estimation beyond crown formation. In archaeological samples, histological analysis established the chronological age of 38 infants from Iberian settlements, ranging from the 30th gestational week to the 2nd postnatal month. The age distribution indicates an attritional mortality pattern, with nearly half dying perinatally, including preterm births. These results support the hypothesis that mortality was mainly due to natural causes. Geochemically, the elemental profiles of Ca, P, and Zn from the outer enamel surface (OES) to the enamel-dentine junction (EDJ) in modern teeth closely resembled those of more recent archaeological samples, indicating good elemental preservation. Across all samples, the NNL showed a slight Zn increase and P decrease. Zn distribution revealed a dynamic, maturation-dependent pattern. In early postnatal stages (in deciduous incisors from individuals with a survival between 10 and 37 days), Zn profiles were flat. By one year of survival, Zn enrichment was evident at both the NNL and near the OES. Teeth that had not completed enamel secretion lacked this enrichment, suggesting that Zn incorporation at the OES occurs during enamel maturation. At one year, a diffusion-like Zn profile extended from the EDJ to the OES, peaking at the NNL and reflecting progressive overprinting during maturation. Other trace elements such as Fe, Mn, Cu, and Ba were more concentrated in archaeological than modern samples, indicating diagenetic changes primarily in the outer enamel and dentin. However, the inner enamel retained its original biogenic signal, supporting the reliability of trace element analysis for developmental studies. Overall, integrating histological and geochemical approaches enhances age-at-death estimations and yields critical insights into early life conditions in ancient populations. These findings offer valuable tools for bioarchaeology, paleodemography, and forensic anthropology, enriching our understanding of past human development, health, and survival.