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

The perception that dinosaurs were much, much bigger than modern animals is false. While they could be very long, most of that came from the neck and tail. The largest dinosaur to exist was the brachiosaurus, which was 20 ft at the shoulder. The largest land mammal ever was the giant rhino, which was 16 ft, only 4 ft shorter.