Grass only appeared in the fossil record 67 million years ago, long after the first plants. Grass became abundant after the extinction of dinosaurs, but it took more than 10 million years to become widespread. Grass is a characteristic feature of the Cenozoic era, and many mammals coevolved with it. Humans lack the necessary adaptations to digest grass.
Because of its structural simplicity, grass might be thought to have evolved a long time ago, along with the first plants. Interestingly, however, the fossil record shows that this is not the case. Grass only appears in the fossil record about 67 million years ago, in the form of phyoliths (tiny flecks of silica in the grass that make it difficult to digest) found in fossilized dinosaur dung. Recently, grass was thought to have evolved only about 55 million years ago, becoming abundant after the age of the dinosaurs, which ended in a mass extinction 65 million years ago, but the phytolith discovery refutes that .
Land plants in general evolved during the Silurian, about 440 million years ago. These were simple mosses and lichens. Throughout the Mesozoic, dinosaurs consumed various plants, but they didn’t touch grass until it came to light at the end of the period. Considering that the entire life span of land plants is one hour, grasses have only evolved in the last nine minutes. However, today many ecosystems are dominated by grasslands, which cover an estimated 20% of the earth’s surface, many animals live on grass, and members of the grass family are the most agriculturally and economically important plants in the world.
About 65 million years ago, the world was decimated by a massive asteroid strike that wiped out all non-avian dinosaurs. The evolution of grasses is often presented in this context, portrayed as the grass colonizing a world left relatively barren by mass extinction. However, this is a mistake, as the grass didn’t become widespread until more than 10 million years after the extinction. While 10 million years is not extremely long in evolutionary terms, it is still too long to be accurate to present grasses as colonizers following widespread plant extinction. Vegetation cover was probably largely restored only a few tens of thousands of years after the extinction, if not before.
Grass is considered one of the characteristic features of the Cenozoic era, which goes from the extinction of the dinosaurs until today. Many mammals exhibit close coevolution with grass, as special adaptations are required to digest its silica-rich tissues. Ruminants such as cows solve the problem by using a multi-chambered stomach that slowly digests grass and ferments it. Using this, they can consume large amounts of grass to sustain themselves. Humans, being flexible omnivores, lack the necessary adaptations to digest grass, opting for higher calorie food sources such as fruits and meats.
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