Modern American movies depict dinosaurs as dauntingly ferocious carnivores. In fact, most mega-massive dinos, regardless of their fearsome horns, spikes and claws, eat plants. They feed on tough cycad leaves, twigs, seeds and fruits of trees common in shrublands and woodlands. Fossilized dino dung (coprolite) shows that while some herbivores mingled tastes, others were fussy eaters.
Thousands of millions of cellulose-fermenting bacteria enable herbivorous dinos to digest the daily tonnage of cellulose (a process similar to that in 20th century cows, elephants and termites). In exchange for their food-processing services, the microbes receive a large tract of habitat.