Increase of body size in sixgill sharks with change in diet as a possible background of their evolution

Abstract

Body size variation of a predator is a simple way to follow the main changes in its food source during its life history or along its evolution in ecology and paleoecology, respectively. Here, we present possible first evidence of such predator-prey co-evolution through the study of the body size evolution among sixgill sharks (genus Hexanchus) inferred from their fossil record and by comparison to the life history of its two recent species. As for the observed ontogenic diet change of the living bluntnose sixgill shark (H. griseus), its ancestors appear to have developed a similar penchant for dining on marine mammals at the end of the Paleogene with a remarkably well-correlated timing.

Keywords:

• Predator-prey
• co-evolution
• hexanchid
• hexanchus
• fossil record

Acknowledgements

Authors thank the Laboratory of Palaeontology, Montpellier University (France) for access to their collections of fresh and fossil material. We thank all the hexanchid collectors, and particularly P. Zenaro, G. Van den Eeckhaut, P. De Schutter and R. Chandler, for their help and/or their contribution by opening their private collections, Dr. H. Cappetta and an anonymous referree for their constructive criticisms and valuable comments.

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