Speculations about the diet and digestive physiology of herbivorous dinosaurs

Abstract

Like living herbivorous lizards, chelonians, birds, and mammals, plant-eating dinosaurs probably relied on a symbiotic gut microflora, housed in a hindgut fermentation chamber, to break down plant cell wall constituents. Large body sizes in most herbivorous dinosaurs resulted in low mass-specific metabolic rates and low rates of digesta passage through the gut; the effects of large body size were probably enhanced by the low metabolic rates of large dinosaurs as compared with large mammals. The long residence time of digesta in the gut permitted long exposure of refractory plant materials to the microflora, probably enabling even those dinosaurs with unsophisticated dentitions to survive on fodder with high fiber content. Large herbivorous dinosaurs probably fed on plants whose allelochemical defenses were geared more toward reducing digestibility than attacking the herbivore's metabolism directly, obviating the need for a foregut fermentation chamber and permitting these large herbivores to take advantage of the energetic benefits of hindgut fermentation for digestion of low-quality fodder. Differences in dentitions among the groups of herbivorous dinosaurs may correlate with differences in standard metabolic rate, activity level, body size, or food quality, or combinations of these factors, but the relative importance of each is difficult to assess. Because the mass of the fermentation contents was probably large in big herbivorous dinosaurs, the heat of fermentation may have been a significant source of thermoregulatory heat for these reptiles.