By the upper Carboniferous (the Pennsylvanian), there are a diversity of plant communities present on land, particularly in low lying areas. The inland areas are probably still pretty sparsely vegetated, if indeed some places had any vegetation at all. During this time the insects are diversifying, other invertebrates are diversifying, and tetrapods are diversifying. So, you might say, OK, can you just cut to the present and quit, we've got everything now, we've got a three dimensional community, we have the vertebrate players, we have the insect players! The answer is no. This is not a modern ecosystem for the following reasons. When we look at the vertebrate players who are present, we find that all of the vertebrates, from their first appearance in the Mississippian until the late Pennsylvanian, are carnivores. None of these guys has any clue that this plant stuff is good to eat.They are too busy eating each other. All of our vertebrate ancestors are busy feeding on the invertebrates, herbivores or detritivores, and energy then flows from the lower level carnivore to higher level carnivore. We've got a terrestrial ecosystem in which there is no vertebrate herbivore and at least in the Mississippian and into Middle Pennsylvanian, not very serious invertebrate herbivores.
This changes in the Middle Pennsylvanian. In the Pennsylvanian we still have the detritivores, but we see the first serious radiation of insects, for which we have a reasonably good fossil record. Several major groups appear at this time, including the insects. Several different plant feeders participate in this radiation. And yes, that is original coloration on the wings of this dragon fly-like creature.
You can figure out what an insect is feeding on by looking at its mouth parts. We find that the world in later Pennsylvanian has a wide range of carnivorous insects but also insects that show both piercing and chewing mouth parts appropriate for feeding on plants. So the great scourge of plants, the insects, finally begin to take over and begins to use terrestrial plants in the Pennsylvanian Plant predators in the form of the invertebrates really begin to get going in the later Pennsylvanian.