Stomach contents of the archaeocete Basilosaurus isis: Apex predator in oceans of the late Eocene
Fig 10
Skull widths as a size indicator for cetacean apex predators in relation to the size of contemporary baleen whales.
For comparisons among whales in terms of their ability to feed on large prey, skull widths are shown with red diamonds for the late Eocene apex predator Basilosaurus isis (CGM 42195); late Miocene apex predators Livyatan melvillei, Zygophyseter varolai, Acrophyseter deinodon, and A. robustus (top down) [67, 69]; and extant apex predator Orcinus orca [70]. These are compared to the increasing limit (dashed line) for mysticete baleen whale sizes (blue circles) through Cenozoic time reported by [72]. Note that apex predators B. isis in the late Eocene and the physeteroid L. melvillei in the late Miocene are larger than contemporary mysticetes, but some late Miocene macroraptorial sperm whales (Z. varolai, A. deinodon, and A. robustus) and extant O. orca are smaller than most contemporary mysticetes. Large size is a common characteristic of apex predators, but large size is neither necessary nor sufficient: the largest mysticetes today are sometimes attacked by O. orca hunting in groups. Note large gaps in our understanding of the history of cetacean apex predators.