Determining the Anatomical Position of the Thoracic Vertebrae with 3D Geometric Morphometrics

Background/Objectives: A common challenge in both forensic and bioarchaeological research is commingling, the intermixing of skeletal material originating from multiple individuals or contexts. To tackle that problem past reassociation methods primarily relied on visual assessment or metric comparisons. However, recent advances in geometric morphometrics show strong potential for improving the sorting of commingled remains. This study applies a three-dimensional (3D) geometric morphometric method to evaluate its effectiveness in reassociating adjoining thoracic vertebrae. Methods: Two vertebral pairs, T4–T5 and T5–T6, from 65 and 73 individuals, respectively, were analyzed. These pairs were chosen due to limited anatomical variability, while they were also the most consistently preserved pairs. All specimens were scanned using a structured-light 3D scanner, and the dataset was derived from three Greek skeletal collections representing different geo-chronological contexts. Fourteen anatomical landmarks were placed on the superior rim and articular facets of the lower vertebra and mirrored onto the lower rim and facets of the adjoining upper vertebra. To remove the size effects the landmark coordinates were converted to Procrustes coordinates, while examining morphological similarity was quantified using Euclidean distances. For each pair, the vertebrae with the smallest Euclidean distances were considered the most probable true anatomical matches. Results: The correct T4–T5 match fell within the three smallest distances in 66.2% of cases, while for the T5–T6 pair, correct matches were found between the first three possible matches in a percentage of 43.8%. These findings indicate that the method can eliminate roughly 50–70% of incorrect matches and therefore narrow the plausible pairings. Conclusions: Future research incorporating more pairs and an expanded landmark dataset may result in greater accuracy for reassociation with 3D geometric morphometrics.