The dynamics of evolution are really interesting. As an aside, we like to say we can't predict what life would be like on an alien world as we only have one dat

The dynamics of evolution are really interesting. As an aside, we like to say we can't predict what life would be like on an alien world as we only have one data point but honestly, I really do wonder if there isn't some universality in the patterns that have evolved here. But I digress. Becoming bigger seems to a strategy driven largely by herbivores as a defense mechanism against predators. Predators seem to get bigger as a response. At least on land. At sea, it seems to work a little differently (eg we have whales that are the largest animals ever to live on Earth that live on very small animals). But being large seems to be a fundamentally risky proposition that sooner rather than later leads to extinction. It just seems harder to adapt. If your food source gets disrupted, it's basically game over. IIRC I read something recently where the megalodon was theorized to have been driven to extinction by the emergence of the (smaller) great white shark that basically stole it's food source (combined with scarcity for other reasons). Then again, dinosaurs were around for 150 million years so what does that say? Was the Earth just relatively stable for that period? Still, dinosaurs died out while birds lived on (and thrived). The end of the last Ice Age killed off a bunch of our larger animals too (eg the wolly mammoth; yes I know it survived in isolation for some time later).