Dental disorders and mandibular trauma: the last stand of the Miocene gymnure Galerix stehlini (Mammalia, Erinaceidae)

Abstract Dental disorders regularly occur in mammals. However, their identification and interpretation in the fossil record are extremely rare. Here, I report cases of dental disorders in fossils of insectivoran mammals in the permanent dentition of the endemic gymnure Galerix stehlini from La Grive-Saint-Alban (Middle Miocene, France). A supernumerary dental alveolus and several second lower premolars showing a varying degree of double-tooth anomaly (including root subdivision) are described for the first time in the fossil record of the Erinaceidae. These malformations are common in the material, suggesting an issue affecting a significant proportion of the time-averaged population. This pattern is interpreted as the result of reduced population size associated with habitat fragmentation. In addition, I report the first observation of dental anomalies in extant gymnures. Non-deleterious dental disorders are common in modern gymnures, especially hypodontia. Given the frequent parallel evolution toward mandibular shortening in erinaceid lineages, premolar hypodontia is interpreted as a repeatedly selected “anomaly”. Finally, a mandibular trauma identified in G. stehlini is described and interpreted as bite marks produced by the upper incisors of a medium-sized galericine, probably Parasorex socialis . The reconstructed bite is consistent with threat-related gaping behavior observed in extant gymnures. Overall, these results suggest that the ecomorphotype of Galerix was relatively unsuccessful by the end of the Middle Miocene.