I like the fact that all animals sort themselves out to fit available environmental niches if they need to. This can most easily be seen with marsupials

[link to biology.clc.uc.edu]
"Eventually, Australia and Antarctica split from each other. Antarctica went to the South Pole and became too cold, killing all the mammals (marsupials) present there. Australia went north to near the equator, and its marsupials thrived. With no competition from placentals. Australian marsupials evolved/diversified to fill all the niches filled by placentals elsewhere: kangaroo are grazers like cattle, koalas eat tree leaves like giraffes, marsupial dogs and Tasmanian devils are predators"

Might this fit in with this theory somehow? (like a "resume factory presets" switch when the population gets too low)
Of course, this would mean there were intelligent dinosaurs.