Why were prehistoric era animals so gigantic in comparison to animals from the “modern era”

Question

Why were prehistoric era animals so gigantic in comparison to animals from the “modern era”

In: 1281

Answer 1

One huge consideration about mass extinction events: When one happens, food becomes incredibly scarce. Smaller animals are able to scrape by with the little food that is left. Megafauna that require literal tons of vegetation to survive starve quickly. Predators that prey on huge herbivores run out of herbivores to feed on.

Little critters manage to eke out a living long enough to arise the undisputed underdog champs of evolution. So multiple mass extinction events lead to adaptable, small, and low maintenance as the biggest factors in long term survival as a species.

After coming out on top from mass extinction events, the lucky megafauna survivors historically encountered something very unfortunate. The little monkeys with sharp sticks.

Edit: grammar