The Mesozoic Era spanned over 180 million years and was a time when immense herbivorous dinosaurs dominated terrestrial ecosystems. Sustaining these colossal creatures required a vast food supply, which came from plant life drastically different from what exists today. The flora evolved significantly from the Triassic through the Cretaceous periods, and this changing menu directly influenced the evolution of dinosaur body plans and feeding strategies.
The Mesozoic Menu: Dominant Plant Life
The early Mesozoic landscape was characterized by the dominance of non-flowering plants, or gymnosperms, which provided the bulk of the available forage. During the Triassic and Jurassic periods, vast forests of conifers, such as the towering relatives of modern redwoods and pines, covered the land. These trees offered tough, resinous needles and woody stems as primary food sources for high-browsing herbivores.
The landscape was also dotted with cycads, which resembled stout palms but were seed-bearing gymnosperms with tough, overlapping leaves. These low-lying, fibrous plants were likely a staple for many mid- and low-level grazers. Other prevalent flora included ginkgoes and seedless vascular plants like ferns and horsetails (Equisetum), which thrived in moist environments.
The Cretaceous period saw the emergence and diversification of angiosperms, or flowering plants. While gymnosperms still provided substantial biomass, the flowering plants introduced softer, more easily digestible leaves, fruits, and seeds. This new food source, which included early forms of magnolias, sycamores, and eventually grasses, added nutritional variety to the herbivore diet. The appearance of angiosperms created new ecological niches, leading to the evolution of specialized dinosaurs adapted to process this softer, more abundant vegetation.
Dietary Evidence: How Scientists Know What Dinosaurs Ate
Paleontologists use several lines of physical evidence to reconstruct the diets of extinct herbivorous dinosaurs. One of the most direct forms of evidence comes from coprolites, which are fossilized feces. Analyzing these coprolites under a microscope can reveal the actual contents of a dinosaur’s last meal, including fragments of wood, spores, and pollen.
Analysis of coprolites often involves searching for phytoliths, which are microscopic silica structures found within plant cells that are resistant to digestion. The discovery of grass phytoliths in the coprolite of a titanosaur from the late Cretaceous, for instance, provided the oldest evidence that grasses existed and were consumed by dinosaurs millions of years earlier than previously thought. The study of dental microwear is another technique, involving the analysis of microscopic scratches and pits on fossilized teeth. Hard, tough foods like conifer needles leave different wear patterns than softer, more abrasive materials like silica-rich grasses, allowing scientists to infer feeding habits.
Herbivores also employed gastroliths, or “stomach stones,” to aid in digestion. These polished stones, often found clustered near the skeleton’s stomach area, were swallowed to help grind and break down tough, fibrous plant matter. The presence and abrasion level of gastroliths provide evidence for a diet that required significant mechanical processing, such as one rich in the tough, woody tissues of gymnosperms.
Specialized Eaters: Linking Dinosaurs to Specific Flora
Different groups of herbivorous dinosaurs evolved specific adaptations to exploit the distinct food sources available in their environment. The massive, long-necked sauropods, such as Brachiosaurus, were high browsers, using their great height to reach the tough foliage of the conifer canopy. Their peg-like or spoon-shaped teeth were designed for stripping leaves and needles rather than chewing, suggesting they consumed bulk quantities of high-fiber, low-nutrient gymnosperm foliage.
Other sauropods, like Diplodocus, possessed forward-pointing teeth that may have been used to strip low-growing plants like ferns and horsetails. The ceratopsians, including Triceratops, were equipped with a powerful beak and a dental battery of shearing teeth for processing tough, fibrous plants. These dinosaurs were low browsers, specializing in chomping and slicing through the dense leaves and stems of cycads and other low-lying, durable vegetation.
Hadrosaurs, or duck-billed dinosaurs, evolved a highly efficient chewing apparatus in the Late Cretaceous. Their dental batteries contained hundreds of teeth that formed a massive grinding surface, allowing them to process large volumes of food efficiently. This adaptation made them ideally suited to exploit the newly diversifying angiosperms, consuming great quantities of the softer, more digestible flowering plant material. The flexibility in hadrosaur diets is also evidenced by coprolites containing conifer wood.