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What Plant Fossils Can Tell Us About Life on Earth

Gregory M. Mueller, Ph.D.
Chief Scientist and Negaunee Foundation Vice President of Science
Chicago Botanic Garden

Fresh off a particularly harsh winter in the Midwest, we at the Chicago Botanic Garden are excitedly watching the flowers in our 30 gardens and natural habitat areas as they continue to bloom. The grounds at the Garden are so beautiful in the spring and summer, it’s hard to imagine there was once a time when flowering plants did not exist.

Dr. Patrick Herendeen, Director of Plant Science and Conservation and a senior scientist at the Garden, is trying to find out exactly when flowering plants came into existence and how they’ve evolved over time. Dr. Herendeen is working alongside a team of researchers from Yale University, Chicago’s Field Museum, Niigata University and the Mongolian Academy of Science to study 120-150 million year-old fossilized plants in Mongolia from the Jurassic and Cretaceous periods. Through their work they hope to better illuminate the world inhabited by dinosaurs from this era, which has fascinated the American public since the dinosaur discoveries of Roy Chapman Andrews in the 1920s.

A slab showing probable fern or “seed fern” foliage
A slab showing probable fern or “seed fern” foliage as well as broad-leaved and needle-leaved gymnosperms. Source: Dr. Patrick Herendeen

Mongolia is a large, sprawling country in Central Asia with most of its population living in one large city, Ulan Bator. The remainder of the country is rural with low population density on its sparse terrain of steppes with mountains and forests to the north and west and the Gobi Desert to the south. Although a number of the plant fossils we study can be – and have been – studied from other localities around the world, the nominal human population coupled with the dry climate has kept fossil specimens undisturbed and particularly well-preserved in Mongolia. Therefore the condition of plant fossils collected by Dr. Herendeen’s team of scientists on expeditions in 2011, 2012 and 2013 will likely yield better and clearer insights than previously studied specimens.

Flowering plants were just beginning to evolve at the start of the Cretaceous period and were consumed by herbivorous dinosaurs (think Triceratops) who likely assisted in dispersing the plants by spreading seeds through their excrement and other means. By the end of the Cretaceous, flowering plants were – and continue to be – the dominant group of plants in most ecosystems, except for boreal and alpine forests dominated by conifers. Interestingly, during the Jurassic and Cretaceous, there were several additional groups of seed plants that went extinct by the end of the Cretaceous. In addition to looking for early flowering plants, we are also documenting these extinct seed plant lineages.

fossilized conifer seed cones
Impression/compression fossils from Early Cretaceous localities in central Mongolia. Isolated conifer seed cones; Source: Dr. Patrick Herendeen

Today, flowering plants form one of only five groups of seed plants living today. Documenting the extinct groups of seed plants is an especially valuable contribution of this research as a complete understanding of the evolutionary history of seed plants is impossible without study of the extinct plants.

Anchoring the bottom of every food chain, you could argue that all life on Earth depends on plants. What we learn from studying their fossils can be a beacon of knowledge on how the planet’s climate has changed over time and yield insights about the future of life on our planet.

Following the expeditions in Mongolia, the team is meticulously examining the collection of fossils in the lab to find clues about how plants have evolved and adapted over time. This is the primary “discovery phase,” as samples are prepared and fossils are recognized, separated from debris, and analyzed. Although analyses are ongoing, it is likely the team will discover completely new, never previously described fossil plants that will add new, significant insights to the bank of knowledge on seed plant diversity in both the past and present.

Stay tuned for more fascinating discoveries as this research progresses!