Question

By the close of the ______ period, therapsids had given rise to early mammals

Answer 1

By the close of the Triassic period, therapsids had given rise to early mammals.

The Triassic period is the era when the therapsid existed.
To be short, Therapsids (which means a group of species related to wild beasts in Latin) are the ancestors of the mammals. They competed in survival with dinosaurs from the Permian era until the Triassic era.