There is an article in Science News about Edmontosaurus.
The tooth dentition seems to indicate that it ate ground plants like grasses.
Well, there weren't grasses as we know them during that time.
Nevertheless, it was ground plants like ferns, not tree leaves.
That's a big distinction,
We paleontologists could already see indications of that with the revised posture
of the hadrosaurs. In the past the first researchers had these duck-billed dinos
walking like humans in a landscape of strange beasts.
But to get the dinosaur skeletons to stand that way, the preparers had to break the tail bones. That's where paleontology and physics clashed.
Now, we understand that these duck-bills were more quadrapedal than bipedal, though they could certainly do both. As quadropeds, the heads of these dinosaurs would be closer to the ground, not up in the trees, or heaven-forbid, eating duckweed in a swamp!
http://www.sciencenews.org/view/generic/id/45126/title/Flexible_molars_made_chewing_champions_out_of_duck-billed_dinosaurs__
