Mesozoic plants and dinosaur herbivory

Abstract

For most of their existence, herbivorous dinosaurs fed on a gymnospermdominated flora. Starting from a simple reptilian herbivory, ornithischian dinosaurs evolved complex chewing dentitions and mechanisms, while sauropodomorph dinosaurs retained the primitive condition of not chewing. Some advanced theropod dinosaurs evolved a bird-type herbivory with a toothless beak and a gastric mill. Dinosaur digestive tract remains, coprolites, and other trace fossils offer little evidence for dinosaur food preferences. Ferns, seed ferns, ginkgoes, and the Cheirolepidiaceae were previously viewed as the food plants favored by dinosaurs. However, animal nutrition science, comparative herbivore physiology, and digestive tract anatomy of modern herbivores suggest otherwise. In fermentation experiments, energy release is much greater in horsetails and most conifers, especially Araucaria, than in many ferns, cycads, and podocarp conifers. Sauropods as bulk feeders must have relied on plants that provided much biomass and regenerated foliage quickly, namely, conifers and ginkgoes. This argues against most ferns and cycads, which offer little biomass and energy.