It's been a while since I've read a paragraph that has wildly changed how I look at the world. I'm so jaded! Anyhow, here it is:
The Recent is a poor analogue for nearly all aspects of Paleozoic ecosystems except for those of the latest Permian. The lack of tetrapod herbivory, the narrow spectrum of plant-insect interactions, the importance of detritivory as the base of the food chain, and the strong partitioning of ecological resource space along widely divergent phylogenetic lines in plants are themes that run throughout most of the Paleozoic. Because of these and other fundamental differences, ecological models based on the present cannot be applied to Paleozoic examples in a uniformitarian manner.
Rough translation: life on land, until about 250 million years ago, was to modern land-based ecosystems much like what a mercantilist, caste-based economy is to a modern market economy. You know the kind: this ethnic group does this, while that ethnic group does that, and those guys? they take care of the horses; and there's never a winner without a loser.
Of course, right after a modern ecology got established in the late Permian, the Earth got whacked with the largest documented extinction event ever. Ah well.