[trengrj]

Great white sharks are so afraid of killer whales that they will leave a feeding area to them for over a year. The killer whales often kill a shark to only eat their liver.

Evolution of cetaceans started around 50 million years ago https://en.m.wikipedia.org/wiki/Evolution_of_cetaceans. You could probably make a solid argument that sharks being displaced as apex predators in the sea would have caused the die out of many species. Perhaps a crossover occurred around 19 million years ago.

[ProjectArcturis]

This was my first thought as well, but oceanic dolphins (the group from which orcas evolved) first appeared just 11M years ago.

[hungryforcodes]

Divergent evolution. Could have been another species / apex predator.