Sorry to nitpickit, but while early members of the homo family could strive in the first few hundred years after the meteor (assuming that theory is correct) hit. The Cretaceous period inwhich the meteor hit, was long after the Stone Age.
The only mammals in the Cretaceous period were also rodents, much less monkeys.
In addition, if the ships were to cause the extinction of dinosaurs, they would still be there for a few hundred more years, because most of the dinosaurs died from not being able to adapt to their newly-blackened sky that impaired their senses of smell.
Other than that it sounds interesting, and I could maybe help with the creatures.