When land masses are fragmentary, when you have lots of islands and little continents, then there's lots of little niches that different species can occupy, and that usually leads to an increase in biodiversity.
As Dan Jardine puts it in his review of Before Sunrise and Before Sunset: These films ask us to consider the very nature and purpose of our existence in a fragmentary, superficial and transient universe.
And there was no clear winner: both sides had fragmentary data and — we now know — some shaky observational evidence that turned out not to be correct.
What fragmentary scientific knowledge was available came from measurements taken by explorers, naval ships, the occasional research expeditions or whaling vessels.