The herbivorous adaptations of Late Triassic and Early Jurassic dinosaurs have been outlined by Galton (1986). The Jurassic period was marked by an abundance of primitive plants and large sauropod dinosaurs. During the Creta ceous, however, flowering plants evolved and radiated, while some of the more primitive types of plant became extinct. It seems highly probable - although impossible to prove - that there was a causal connection between these events, and that the success of the ornithopod dinosaurs was a reflection of their ability to feed upon the newly evolved phanerogams (see discussion in Tiffney 1997).

Indirect evidence as to what herbivorous dinosaurs fed on is plentiful. This is based on contemporary vegetational surveys, and on hypotheses regarding foraging abilities inferred from functional morphology. There is little direct evidence, however, to indicate what plants they actually ate. Fossil trackways sometimes provide information (Farlow and Chapman 1997; Lockley 1997). For instance, the tracks of Cretaceous dinosaurs around fossil tree trunks, described by L.R. Parker and R.L. Rowley Jr. in 1989, suggest the shuffling footsteps of browsing hadrosaurs. Seeds, conifer twigs and pine needles have been found in the body cavity of a fossil Edmontosaurus. These could have been the stomach contents or, equally well, represent debris washed into the decayed carcass. Finally, the coprolites of herbivorous dinosaurs - although much less common than those of carnivores - have occasionally been found. Even so, they have often been partly decomposed, or devoured by dung beetles before fossilisation and it is difficult to know what species of dinosaur produced them. Most are composed mainly of conifer stem tissue, indicating a highly fibrous diet. Many have been found in close association with the hadrosaur Maiasaura, which had a battery of grinding cheek teeth that could easily have chewed wood (Chin 1997).

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