I may have mentioned this before, but as I was expanding my geologic ages list, I was struck by it. Again, I think.
Although to the mainstream mind, dinosaurs are synonomous with "really old", I actually think of them as a kind of modern type animal, really. To me, the "really old" faunal assemblages predated the dinosaurs. The first dinosaurs came on the scene at roughly the same time as the first mammals, and I'm firmly in the camp that believes that they had similar physiological advances and were "on the same page", so to speak, as being the two most exciting and happenin' groups of tetrapods on the planet. The dinosaurs took a good 28 million years from their first appearance to their complete domination of the megafaunal assemblages, but once they got there, they didn't let go for another 132 million years. That's a total lifetime of over 160 million years (because I rounded down the fractional million years), and if you count the birds as dinosaurs, as most dinosaur paleontologists are wont to do these days, then they've got 226 million years of seniority, and were running the show for much of that.
So I was a little bit surprised when I put together my timeline, starting in the Devonian when the first tetrapods climbed out of the water and explored, tentatively, the terrestrial world for the first time, and discovered that the pre-dinosaurian "ancient times" passed much more quickly than I thought. Vascular, terrestrial plants barely squeeked in at the end of the Silurian, and didn't really become common or important until during the Devonian. Within 10-15 million years of these first forests, Acanthostega and Ichthyostega, the earliest known tetrapods, are found, a mere 360-370 million years ago. I say mere, because the first dinosaurs and first mammals appeared in the Late Triassic about 228 million years or so ago (well, that's when the earliest ones have been found. They already show some signs of diversity, indicating that they're probably a few million years older, actually). It only took 132-143 million years to get from "the first ever vertebrates made their tentative steps onto land" to "essentially modern faunas dominate the terrestrial ecosystems." And then the dinosaurs stepped in and dominated terrestrial ecosystems for longer than it took to get from "barely more than a fish" to "a dinosaur" in the first place.
For some reason, that realization is both somewhat awe-inspiring and humbling. The staggering age of the world, and the staggering amount of investment in its creation, to get to the point where we could come on the scene, is humbling.