They had the best grazing teeth ever evolved. The plants at the time must have been ultra tough to produce what I presume to be epigenetic changes for adaptation. Current grazing teeth are not as complex. Evolution going backwards? No, just built-in adaptation by the evolutionary process. It is obvious evolutionary life can do anything it has to at any stage of evolution.-http://phys.org/news/2012-10-fossilized-teethduck-bill-dinosaurs-plant-pulverizing-teeth.html