The one for me which was quite surprising is how recent grasses are. Grass is 110M or so year old, but grasses as we know them - the plains, covering vast spaces, etc. - the C4 grasses, are all in the 5m-15M years ago period. Imagine an earth with no sprawling grasses.
I found that surprising when I learned about it. Grass did not exist yet at the time of the dinosaurs. In good documentaries, artistic representations of dinosaurs may show them among ferns and trees, that did exist. But if I see grass I will know the team did not do a good job!