It's probably implied somewhere that the KT asteroid was part of their life seeding program that started by eliminating predominant species. They would most likely look for the right conditions on a random planet to support life and then inject the biosphere with their creation.

Not quite Star Trek, but Rick & Morty did an episode with that as a plot point recently in the season where they only travel the galaxy, not the multiverse. Every planet had some form of prehistoric life, with the interpretations of what they found having more or less the same effect on society, but with different silly names.

Was just fun to see the idea explored. Trek would have probably taken it a bit more seriously though.

I'm not sure exactly what you mean, but i would imagine any place with life will have mass extinction events and that will make it likely that there has been at least one period before the current sapient species where there was a different group of animals in prominence.