Ten million years later there were mammals the size of elephants. I will admit right off, I could be deeply misinformed or somewhat delusional, so let me know. The easy answer was it wasn t big enough. Mammals had several survival advantages over dinosaurs for surviving a cataclysmic asteroid collision. One was that they were smaller, had larger populations and shorter maturation periods.
Larger populations mean their species have more potential survivors.
Shorter maturation periods mean they produce more offspring and thus may evolve adaptive traits faster.