A shark mystery millions of years in the making

The paper An early Miocene extinction in pelagic sharks [1]:

> We present evidence for a previously unknown major extinction event in sharks that occurred in the early Miocene, ~19 million years ago. During this interval, sharks virtually disappeared from open-ocean sediments, declining in abundance by >90% and morphological diversity by >70%, an event from which they never recovered. This abrupt extinction occurred independently from any known global climate event and ~2 million to 5 million years before diversifications in the highly migratory, large-bodied predators that dominate pelagic ecosystems today, indicating that the early Miocene was a period of rapid, transformative change for open-ocean ecosystems.

[1] https://science.sciencemag.org/content/372/6546/1105

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.

What on earth happened there? What are the wild guesses experts having a pint or two could come up with? (i.e. since there is no data for conclusive evidence, what are the scenarios that could maybe cause something like this)

Subtitle got promoted to title?