Miocene marine vertebrate trophic ecology reveals megatooth sharks as opportunistic supercarnivores

Abstract

Trophic interactions play pivotal roles in marine vertebrate ecology and evolution. Yet, these parameters are especially difficult to determine in fossil communities. To elucidate past trophic palaeoecology, we apply the zinc isotope proxy in a comprehensive analysis of 19 taxa from an early Miocene marine ecosystem, including the megatooth sharks Otodus megalodon/chubutensis. We find substantial resource partitioning among these taxa, with at least three distinct trophic positions and a general increase in body size of taxa towards the top of the food web. The white shark (Carcharodon carcharias) ancestor Carcharodon hastalis had a distinctly different trophic ecology compared to modern C. carcharias, corresponding to the evolutionary gain of tooth serrations between the two species. A comparison among fossil assemblages indicates that megatooth Otodus sharks possessed a higher dietary flexibility on a population level than previously understood, suggesting that they were opportunistic supercarnivores capable of foraging throughout the food web.