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

From what I understand, prehistoric animals were so large because there was much more oxygen in the atmosphere, more oxygen means larger animals. As for the blue whale which is considered the largest animal on the planet to date, they’re large because they have a slower metabolism, they don’t use energy as quickly and the cooler waters provide more oxygen for them. Paramount Plus did a great documentary on this exact topic and it would answer a lot of your questions.