Dinosaurs were very large compared to today's land mammals, for example elephants. This is because the mammals were the mesizoic equivalent of mice, rats, and shrews were mammals. The mammals held the small warm blooded niches The Mesizoic has some very big mysteries. Why were dinosaurs so big compared to the mammals that lived in the Cenozoic, the last 65 million years, sometimes called the age of mammals? Given that the proto-mammals, also called therapsids, became warm blooded millions of years before the proto-dinosaurs, also called archosaurs, why were the proto-dinosaurs able to evolve in the first place. One would think that newly evolved warm blooded animals would be relatively inefficent and therefore would be quickly eliminated. Once your found the fatal errors in my reasoning you can pass on your insights in my guest book.