Well, as usual when teaching plant diversity, you get to angiosperms just at the end of the semester, but only by moving through gymnosperms rather quickly. Angiosperms are the last major plant group to appear in the fossil record, and that appearance is about 135 million years ago. So let's see that's almost 45 million years a lecture. Wow! Time to get moving; a lot can happen in this period of time. Consider this, the extinction of the dinosaurs perhaps due to a major asteroid impact occurred 65 million years ago, the event that defined the end of the Cretaceous. The vast majority of mammal evolution has taken place since then. Think about this. Grasses hadn't evolved yet, some thing that was necessary before the large mammalian herbivores could evolve, something that turned little forest understory browsers into the horse you are familiar with today. Some of the dinosaurs were pretty big browsers too, but their primary food was ferns, conifers, and cycads. What a change! And of course the very recent intimate interaction between humans and plants in the form of agriculture has produced some winners (maize, soybeans) and some losers (tallgrass prairie plants).