What were the first large animals to inhabit the Earth?

Question

I mean way back before the dinosaurs. My friend told there were animals that had a three fold symetry unlike the twofold that dominate the earth. The starfish has fivefold. That seems to work to an extent. What were the first bold experiments on the part of evolution that didn't (or did) quite make it?

Answer 1

Wooly Mammoth

Answer 2

Before the dinosaurs there was water the large animal to inhabit the earth had to be the giant squid. Or a very large giant fish or maybe a huge jellyfish.