Bifid rib in bioarchaeological material on the example of new cases from Poland with literature review and proposal of classification

The anomaly known as a bifid rib is difficult to quantify in bioarchaeological collections not only because of its rarity in the population itself (less than 1.5%), but also because of vulnerability to postmortem damage of this part of the skeleton as well as similarity to other developmental anomalies, which can lead to its misidentification. This work presents five cases of rib bifurcation (from four individuals) from four different populations living in Kujawy region in north-central Poland from the Neolithic until the Early Modern Era. Morphological analyses are matched by a paleoradiological investigation. Furthermore, this study endeavours to summarize all known cases of rib bifurcation in archaeological collections and discuss the correctness of the diagnoses. Additionally, criticism of the arguments allegedly proving the presence of naevoid basal cell carcinoma syndrome (NBCCS, Gorlin-Goltz syndrome) in the archaeological populations based on available photographic data of bifurcated ribs and associated anomalies is made. Finally, a new proposal for the classification of this anomaly in osteological material is presented.