Trivia: During what geologic period did mammals become the dominant animal group?
Tertiary
Denovian
Cambrian
Cretaceous
The correct answer is Tertiary
So why is this answer correct? : In one fell swoop, an asteroid ended the Cretaceous period — and even the longer Mesozoic Era — and the resulting Tertiary period saw the rise of mammals. Just as the Great Dying cleared the slate for dinosaurs hundreds of millions years earlier, so too did early mammals benefit from the dinosaurs’ widespread destruction — and life continued on.