After the dinosaurs went extinct, mammals got 1,000 times bigger, and here’s why. With the dinosaurs out of the picture, there was a lot more space and food available for the surviving mammals. This allowed them to grow larger and take over the ecological roles that the massive dinos had filled. Bigger mammals could better defend themselves, explore new environments, and find diverse food sources. Plus, the climate and habitats favored these larger mammals, leading to the giants we see in the fossil record. Credit:br Brontotherium hatcheri: By Postdlf, CC BY-SA 3.0 , Animation is created by Bright Side.