On the ecotrophic role of the giant Neogene shark Carcharocles megalodon: some notes from the Pisco Formation of Peru

The extinct otodontid shark species Carcharocles megalodon is known by giant serrated teeth and large vertebrae from Mio-Pliocene marine deposits worldwide. Reaching a total body length greater than 16 m, C. megalodon is regarded as an apex predator which likely occupied the top of the trophic chains of the Neogene global ocean. Despite C. megalodon being interpreted as a whale-eating predator, and its fossil remains being common in Neogene deposits worldwide, little direct evidence for the trophic ecology of this mega-toothed shark arose from the fossil record to date. We report on long and serrated shark bite marks attributed to C. megalodon affecting fossil mammalian bones collected from late Miocene shallow-marine deposits of the Pisco Formation exposed at Aguada de Lomas (South Peru). These occurrences, the first in their kind from the Southern Hemisphere, significantly expand the record of bite marks of C. megalodon; moreover, for the first time a prey of C. megalodon is identified at the specific level (as Piscobalaena nana, a diminutive member of the extinct mysticete family Cetotheriidae). Due to the fragmentary nature of the studied material, it was not possible to ascertain if the observed bite marks were due to scavenging or to active predation. Nevertheless, based on actualistic observations and size-based considerations, we propose that small-sized mysticetes (e.g., P. nana) could have been one of the target prey of adult C. megalodon. A predatory behavior somewhat similar to that of the great white shark attacking seals may be hypothesized for C. megalodon preying upon small mysticetes. We suggest that C. megalodon was a generalist apex predator whose trophic spectrum was still focussed on small-sized baleen whales. It is therefore interesting to observe that the extinction of C. megalodon (occurring at the end of Pliocene) roughly coincides with the the decline and fall of various lineages of small-sized baleen whales (including most Cetotheriidae). The disappearance of the last mega-toothed shark could thus have been triggered by the collapse of the archaic diminutive mysticetes (mostly inhabiting coastal upwelling-influenced waters of warm to temperate oceans) in favor of modern gigantic baleen whales (seasonally migrating to high latitude cold waters), the latter event being possibly driven by long-term planetary oceanographic and climatic changes.