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

I heard on a podcast that it was because they breathe like birds, which makes sense. When we breathe in, we take in oxygen on the inhale. Birds absorb oxygen twice, on the inhale and the exhale. I’ve only heard that once. I have no idea if that’s the actual reason, but I thought it was interesting.