As colossal dinosaurs roamed the Earth and dominated the land, you might picture contemporary mammals as equally grand and formidable hunters, but the truth could be quite a surprise. During the age of dinosaurs, what was the average size of most mammals?

Seriously, trying to compete with a T-Rex? Get real! Mammals during the dinosaur era were super low-key, mostly living underground or in trees, munching on insects and seeds. Paleontologist Roger Smith and his team published research in the 2017 journal *Nature*, revealing that analyzing fossil records showed Mesozoic mammal evolution favored smaller sizes to avoid large predators, i.e., dinosaurs. Forget those movie scenes with saber-toothed cats fighting dinosaurs; that's just Hollywood messing with your head!