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

Mostly there just weren’t any humans to extinct them. We are an existential threat to all sorts of fauna, but more so for the larger species. It’s either domestication or eradication, humans don’t tolerate competition.