How did grasses alter Earth’s ecosystem?

June 8, 2015
Caroline Strömberg
Collecting phytolith samples from the middle Miocene Railroad Canyon section in Idaho.

Undergraduate student Erik Fredrickson extracting phytoliths from ancient soils in the Strömberg lab.
Photo: Burke Museum

Caroline Strömberg and postdoctoral researcher Georgina Erra collecting phytolith samples.

Caroline Strömberg and postdoctoral researcher Georgina Erra collecting phytolith samples at Mata Amarilla type section, Santa Cruz province, Argentina.
Photo: Burke Museum

Extracting phytoliths from ancient soils.

Undergraduate student Erik Fredrickson extracting phytoliths from ancient soils in the Strömberg lab.
Photo: Burke Museum

Imagine a world without grasses: no popcorn, cereal, bread, rice, pasta, tortilla chips... no bamboo floors, golf courses, or lawns. Half of Earth’s land surface would be covered by a different vegetation type than it is today, and all of the animals that depend on grasses and grasslands—our own species included—would be without their natural habitat. Yet only 30 million years ago, the world lacked its many grass-dominated environments (savannas, prairies, woodlands) and 70 million years ago, grasses had not evolved—or so we think.

How did one group of plants (grasses, or “Poaceae”) completely alter Earth’s ecosystems? How did this transformation influence the evolution of animals?

Curator of Paleobotany Dr. Caroline Strömberg and her students use plant fossils to answer these questions. Specifically, they study tiny crystals (phytoliths) that form inside tissue in living plants and are left in the soil—sometimes for millions of years—after the plant dies, offering evidence of what plants grew in a spot. Many types of grasses have unique phytoliths that allow the Strömberg lab to track the evolution of grasses and the spread of grasslands.

To do so, they travel to field sites around the world (from the U.S.’s Great Plains to China and Argentina) that span in age from the Pliocene (3 million years ago) to the Late Cretaceous (100 million years ago). From cliffs where the rock is exposed, they collect samples from ancient soil horizons.

Afterward, they treat the samples with chemicals to extract the tiny fossil phytoliths, which can then be studied using a microscope with very high magnification. With any luck, there are phytoliths from grasses and other plants preserved that can provide a glimpse into an ancient world.

Grass phytolith from an open-habitat grass discovered in the ancient soils

Grass phytolith from an open-habitat grass discovered in the ancient soils at Gran Barranca, Chubut Province, Argentina.
Photo: Burke Museum

Grass phytolith from an open-habitat grass discovered in the ancient soils.

Grass phytolith from an open-habitat grass discovered in the ancient soils at Gran Barranca, Chubut Province, Argentina.
Photo: Burke Museum

In one of the Strömberg lab’s ongoing projects, graduate student Elisha Harris is studying how vegetation structure and faunas changed in northern Idaho during the latest major warming event on Earth, the so-called Mid-Miocene Climatic Optimum (MMCO), 14–17 million years ago. By doing so, she will learn how ecosystems respond to global warming over longer timescales. This information might also be useful for predicting how our current ecosystems will fare in the face of anthropogenic climate change.

In another project, Dr. Strömberg and postdoctoral researcher Dr. Georgina Erra traveled to southernmost Patagonia to collect rocks from the time of the dinosaurs. They hope to trace the steps of the earliest grasses, which are thought to have lived in South America, to better understand what kinds of environments allowed these remarkable plants to evolve.

A third project, which involves former Paleontology Collections Manager, Dr. Regan Dunn, a former member of the lab, seeks to shed light on how vegetation and faunas changed in Patagonia in response to environmental change during the last 50 million years.

To learn more about research on grasses and grasslands, visit the Strömberg lab webpage.

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