Wear pattern of the molar dentition of an extant and an Oligocene bat assemblage with implications on functionality

Abstract

Wear stages have been defined based on dentine exposure at the lower molar surfaces for a population of the extant bat Pipistrellus pipistrellus (6 wear stages) and for a sample of the Oligocene bat Pseudorhinolophus antiquus (4 wear stages). Wear stages 1–2, which occur in juveniles, are characterised by punctual dentine exposure on the cusps and ridges. Wear stages 3–4, found in adult individuals, are characterised by connected areas of band-shaped dentine. The last two wear stages (5–6) reflect the dental condition of old (senile) individuals, with the molar surface showing wide areas of exposed dentine and the occlusal relief drastically reduced. The defined wear stages of the P. antiquus sample are comparable to stages 3–6 of P. pipistrellus. The molars of both species show wear facets with striations that go in two directions, indicating a two-phased, bucco-lingually directed masticatory movement which gains more freedom with progressive wear. This development underlines that shear-cutting dominates in the early stages of the mastication process, whereas in later stages a crushing component becomes increasingly dominant. Based on the average age determination of individuals from the defined wear stages, about 90 % of the studied P. pipistrellus population consists of juveniles (wear stages 1–2). In contrast, wear stages 3–5 (95 %) predominate in the studied sample of P. antiquus, indicating that most of the individuals were of an adult/senile age.