Age of the Mammals
There is often speculation about whether mammals would have succeeded in displacing the dominant dinosaurs even without the catastrophic meteorite impact. However, the global evidence of this impact, namely a layer of ash in the relevant sediments, suggests a direct connection. While some dinosaur lineages had already gone extinct before the impact, only one lineage survived: today’s birds.
Even after the major impact, there were continued smaller catastrophes that led to extinction events among mammals as well, followed by subsequent radiations and expansions.