Why were dinosaurs (and other organisms) so big?

Question

I understand that in Carboniferous era insects were big because of oxygen but what about other creatures?

Why were some dinos as big as whales? Why were a lot of them many times bigger than elephants? How does it work? If mammals reigned in those eras instead of dinos and insects, would they also be this gigantic compared to modern ones? (Like gigantic sloth but 5 times the size of it?)

In: Other

Answer 1

Dinosaurs had some skeletal adaptations that allowed them to grow much bigger than the theoretical largest (land) mammal. Sauropods in particular were so titanic because of how their spines evolved.