Dental microwear texture analysis on extant and extinct sharks: Ante- or post-mortem tooth wear?

Abstract

Sharks are apex-predators that play an important role in past and present aquatic food webs. However, their diet - especially in extinct species - is often not well constrained. Dental microwear texture analysis (DMTA) has been successfully applied to reconstruct diet and feeding behaviours of different aquatic and terrestrial vertebrates. However, unlike in mammals, food-to-tooth contact in sharks is rather limited because only larger prey is manipulated before swallowing. Together with a fast tooth replacement rate, this reduces wear on individual teeth. Here, we present an explorative study of dental microwear texture on extant and extinct sharks to test whether ante-mortem wear is related to ingested diet or habitat preferences and resistant to post-mortem alteration processes. Shark teeth from 24 modern species and 12 fossil species from different localities were measured. As an additional comparison, extant shark teeth of Carcharhinus plumbeus were tumbled in sediment-water suspensions to simulate post-mortem mechanical alteration by sediment transport. Only three of the twelve extant shark species with three or more specimens had significantly different dental surface textures. Furthermore, no clear relation between food or habitat preferences and ante-mortem dental wear features was detected for this sample set. Tumbling modern shark teeth with siliciclastic sediment of four different grain size fractions led to increasing complexity of the dental surface. Fossil specimens resemble these experimentally altered shark teeth more in complexity and roughness. Thus, fossil shark teeth seem to display either very different (e.g. harder) diet-related wear or a strong degree of post-mortem alteration. Based on our restricted sample size, dental wear of shark teeth does overall not seem to simply reflect dietary differences; hence, it is difficult to use DMTA as reliable dietary reconstruction, in either extant nor extinct sharks.