Why were animals so much bigger in prehistoric times?

Question

Dinosaurs seemed to have generally been so much larger than animals today. Huge dragonflies that dwarf their modern counterparts, turtles 10ft long. What is the mechanism that allowed them to be so large, or conversely makes modern ones smaller? Is it about Oxygen levels, or efficiency, or something else?

In: 296

Answer 1

They weren’t. The [largest animal ever](https://en.wikipedia.org/wiki/Largest_and_heaviest_animals) is contemporary.