In the course of hundreds of millions of years the world's oceans have expanded and contracted in response to the shifting of the Earth's tectonic plates and to changes in climate. There were periods of the planet's history when vast areas of the continents were flooded by shallow seas such as the shark and mosasaur infested seaway that neatly split North America during the age of the dinosaurs.

As those epicontinental seas drained, animals like mosasaurs and giant sharks went extinct, and conditions on the marine shelves where life exhibited its greatest diversity in the form of things like clams and snails changed as well.

It will be interesting to see the reverberations of this line of thought over the next several years.