Which era had the most mammals and birds?

The answer is Cenozoic in the beginning of this era there were few mammals and birds but longer down the road more animals appeared as the era continued.

And so my answer would be Cenozoic but i am not completely sure.:(

ANSWER ABOVE IS INCORRECT

Mesozoic is the correct answer small mammals evolved during the Mesozoic era, with reptiles, as did birds. The full potential and releasing of mammals came in the Cenozoic, when the mass extinction of 20% of the Mesozoic's species happened.