Why are all the ‘prehistoric’ versions of animals so massive?

Question

We always hear about how big ancient sharks, alligators, birds were. What was the advantage of being such a massive size and what caused them to become smaller? To my understanding its best to be smaller because of the square-cube law, then why are there exceptions like whales?

In: 3

Answer 1

You already know about squares and cubes, good.

In short, there was a higher concentration of oxygen.