I want to know the answer to the following question:
What species dominated the seas?
All the background I'm provided with is that "Seasons came back into effect and the poles got seasonally colder, but dinosaurs still inhabited this area like the Leaellynasaura which inhabited the polar forests year-round, and many dinosaurs migrated there during summer like Muttaburrasaurus.". Is that enough to answer the question?
Answer: no