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

The Rise of the Grasses. In north america after the last ice age there was a regime change in the type of plants which covered the ground. Mammoths like the ones that lived in San Jose, California 8 thousand years ago could not have survived on the native plants which exist here now because the caloric density per square mile isnt high enough to support these animals.