Did Grass Exist During the Age of Dinosaurs?

The popular image of a Brachiosaurus munching on treetops or a Triceratops in a meadow often includes a familiar green carpet of grass. This vision of dinosaurs in grassy fields is a staple of books and movies, prompting a question about their environment: did the vast, open grasslands we associate with large herbivores exist during the Age of Dinosaurs?

The First Appearance of Grass

For most of the time dinosaurs walked the Earth, grass was entirely absent. The Triassic and Jurassic periods unfolded across a world without a single blade of grass, as the evolutionary story of grass (family Poaceae) begins much later. The first definitive evidence for grass appears only at the very end of the dinosaur era, during the Late Cretaceous period.

The evidence comes from fossilized dinosaur dung, or coprolites. Scientists analyzing coprolites from the latest Cretaceous in India discovered microscopic silica structures called phytoliths. These phytoliths have unique shapes that act as a cellular signature for plants, and the ones found in the dung were unmistakably from early forms of grass. This indicates that some of the last dinosaurs, likely titanosaurs, did consume primitive grasses.

Fossil discoveries in China have pushed the origin of grass back even further, with microfossils found on the teeth of a hadrosaur from the Early Cretaceous. These finds suggest that the earliest grasses were present in limited, forested areas. However, they were a minor component of the global flora and did not form the expansive prairies or savannas widespread today.

The Mesozoic Era’s Dominant Flora

Instead of rolling grasslands, the Mesozoic Era featured a dramatically different plant landscape. The dominant ground cover for much of the dinosaur age consisted of vast “fern prairies.” These expanses were thick with ferns of all sizes, from low-lying varieties to large, tree-like ferns that created a dense understory in many regions.

The forests were equally distinct from modern woodlands. Towering conifers, similar to today’s pine trees and redwoods, were abundant. Interspersed among them were other gymnosperms that are rare today, such as palm-like cycads, ginkgo trees, and the now-extinct Bennettitales. Horsetails, ancient vascular plants that still exist in moist environments, grew in dense thickets.

This flora created a world dominated by spore-producing plants like ferns and seed-producing but non-flowering gymnosperms. Flowering plants, or angiosperms, did appear during the Cretaceous period. However, widespread grasslands only emerged millions of years after the dinosaurs had vanished.

The True Diet of Herbivorous Dinosaurs

With a world largely devoid of grass, herbivorous dinosaurs evolved to exploit the plant life available to them. Low-browsing dinosaurs, such as the heavily armored Ankylosaurus and the plated Stegosaurus, were well-suited for a diet of ground-level plants. They likely consumed large quantities of ferns, small cycads, and other low-growing foliage.

Towering, long-necked sauropods like Brachiosaurus and Diplodocus were adapted for a different feeding strategy. Their immense height allowed them to browse the high canopies of Mesozoic forests, reaching the leaves of tall conifers and ginkgoes. Some sauropods had peg-like teeth, which scientists believe were used for stripping leaves or even pinecones from branches.

Evidence for these ancient diets comes from several sources. The anatomy of dinosaur jaws and teeth provide strong clues, as some had complex batteries of grinding teeth for tough plant matter, while others had simpler teeth for pulling vegetation whole. The most direct evidence comes from coprolites, which can preserve undigested plant fragments, pollen, and phytoliths that reveal the last meals of these giants.