Plants Figuring out the relationship between plants and dinosaurs can be revealing, but is difficult to do. The problem is not for a lack of specimens. Plant fossils easily outnumber bone fossils and they come in many more forms. The billions and billions of tons of coal in the world are ancient plant remains, as are compressed leaves, leaf imprints, pollen grains and pieces of fossilized wood. The difficulty is that bone fossils and plant fossils are rarely found at the same site.
Plant matter is preserved best in an acidic environment, like in a peat bog.
Whereas bones, having a lot of calcium in them, are essentially demineralized by acidic conditions. Conversely, if you take a piece of plant and drop it in a nice alkaline soil where a bone would likely be preserved, the plant is going to be degraded, not only by the chemical conditions, but also by all organisms that live in the soil. Despite this wrinkle, plant groups of the Mesozoic are well known. Flowering plants, or angiosperms, first appeared near the end of the Mesozoic, around 144 million years ago, and quickly took hold, constituting nine-tenths of all known plant species by the end of the period. Grass, so common today, was completely non-existent.