A week ago, I learned that animals weren't bigger in the past.
Sure, there were dinosaurs that were quite big, but they weren't living all at the same time. So there was maybe a big one, that died out, and the next big one would evolve much later.
As this project shows, the biggest animals and plants are living right now.
Also, we're living in the time with the biggest spiders in history. Somehow they don't get that big on average. Turns out, the high oxygen levels in the past didn't affect arachnid sizes as much as insect sizes.