answersLogoWhite

0

No, they came later. During the last two periods of the Mesozoic (Jurassic and Cretaceous) all the mammals were small and primitive, as the dinosaurs held all the important positions (called "niches"). When the dinos shuffled off, the mammals began to expand in size and complexity to fill the vacancies.

User Avatar

Wiki User

12y ago

What else can I help you with?