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

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.