Dental paleopathology in fossil rhinoceroses: etiology and implications

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Abstract
The identification and interpretation of paleopathological findings in the dentition of mammals have the potential to shed light on disturbed development and stress conditions. In combination with knowledge about the timing of dental development, dental pathologies can provide a unique opportunity to reconstruct specific phases in the life history of fossil taxa, as well as animal‐environment interactions. The dental ontogeny of the extinct rhinoceros Prosantorhinus germanicus from the Miocene is well‐known from an exceptionally preserved sample of juvenile dentaries. Two of the represented juvenile individuals each revealed a dental anomaly, which were analyzed macroscopically and via X‐ray tomography in this study. One specimen documents decreased dental wear of deciduous cheek teeth, mandibular bone resorption as well as abnormal cemental deposition. At an early age, the extinct juvenile rhinoceros probably was affected by a gingival infection resulting from an accumulation of bacterial plaque. This led to a chronic gingivitis and eventually may have caused periodontitis. Furthermore, it suffered from inflammation‐induced hypercementosis. Another specimen revealed an abnormal reduction in thickness of enamel in the deciduous cheek tooth. The enamel hypoplasia indicates stress experienced during the prenatal period. During a phase of environmental stress (e.g. increased fluoride exposure) or physiological stress (e.g. malnutrition) the function of the secretory ameloblasts was disrupted in the developing embryo. The present work shows that the analysis of dental paleopathologies is a useful means for retrospective assessment of specific phases in the life history of extinct animals. This adds to the picture of the living conditions of the extinct rhinoceros P. germanicus.

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