Pre-Messinian ecological diversity of Mediterranean sharks revealed by the study of their dermal denticles

Abstract

The Messinian salinity crisis (~5.59 Ma) is regarded as one of the most determining events for the recent evolutionary and palaeobiogeographic history of the Mediterranean biota. The impact of such episode has usually been assessed by evaluating the associated taxonomic turnover, however its consequences have rarely been interpreted from an ecological perspective. Here we assess the functional diversity of shark dermal denticles in a Serravallian locality from southeast Spain, providing a primary view into the pre-Messinian ecological diversity of shark communities from the Western Mediterranean. Our results reveal a high diversity of functional types of dermal denticles including dermal denticles that prevent the settlement of ectoparasites and epibiontes, abrasion resistant dermal denticles, drag reduction dermal denticles and dermal denticles with less specific, or more generalized, functions. This variety of dermal denticles supports the presence of several ecological groups of sharks such as schooling and strong swimming species and, possibly, demersal species, slow sharks of the open water bioluminescent taxa. Therefore, the application of this methodology to Pliocene and Pleistocene fossiliferous sites will be crucial for unravelling the impact of Messinian salinity crisis and other recent geological events from an ecological perspective, allowing us to understand the shark communitycompositionand diversityof the current Mediterranean Sea.