Eli5. – How were prehistoric species able to be so much larger than current species?

Question

I feel that there must be some physiological stressors or environmental factors that inhibit modern organisms of all domains from reaching the size, of say, a megaladon or brontosaurus.

In: 18

Answer 1

Were they though? We currently have the largest animal to have ever existed on the planet living in our lifetime. The Blue Whale