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Fossil plants provide clues to changing environments in Tennessee’s past

Dr. Elizabeth Hermsen examines plant fossils during a research trip to the Gray Fossil Site collections. (Photo contributed by David Moscato)

From Staff Reports

The Gray Fossil Site is famous for preserving the remains of a 5-million-year-old Appalachian ecosystem. Not only do these fossils include a variety of ancient animals like rhinos, mastodons and pandas, they also include a forest’s worth of ancient plants. And that list of plants is now a bit longer thanks to a pair of recent studies identifying two extinct Gray Fossil Site plant species that are entirely new to science.

The past several million years on Earth have been marked by dramatic climatic and environmental change, but few fossil sites are known in the Eastern U.S. where paleontologists can investigate this time period. The Gray Fossil Site, which is overseen by the Don Sundquist Center of Excellence in Paleontology at East Tennessee State University, is one of those rare few, so these two new plants help fill in the picture of how this part of the world has changed over time.

The first of the new species is named Corylopsis grisea, a member of the witch hazel family. The species name, grisea, comes from the Latin word for the color “gray,” named in honor of the Gray Fossil Site. Modern species of Corylopsis, commonly called winter hazel, are shrubs and trees native to eastern Asia. This new species, identified from fossil seeds, thus joins a growing list of extinct Gray Fossil Site plants with close relatives living in modern-day Asia.

“In the past, the floras of the northern hemisphere continents were more connected than they are today,” said Dr. Elizabeth Hermsen, co-author on both new studies and research scientist at the Paleontological Research Institution in Ithaca, New York. “This connection was facilitated by a warmer global climate, land bridges in the North Atlantic and North Pacific regions, and, in some areas, more precipitation than occurs today.” Over time, environmental changes led certain plants to go extinct in some regions while they survived in others.

Until this study, all Corylopsis fossils from North America have been over 30 million years old, so scientists thought these plants had vanished from the continent by then. But the discovery of this new species at Gray reveals that Corylopsis hung on much longer. It may be that the warm forest environment of the Gray Fossil Site was a safe haven for plants like Corylopsis, even as most of the continent became uninhabitable for them.

The second new plant species is named Cavilignum pratchettii. In this case, both the genus, Cavilignum, and species, pratchettii, are new, making it the first extinct genus of plant identified from the Gray Fossil Site.

Cavilignum is a bit of a mystery. It is a flowering plant, likely a woody shrub or tree, but with only fossilized endocarps (the hard center of the fruit, like the pit of a cherry) to work from, the researchers are unable to identify what its living relatives might be.

“It is certainly possible that it could represent a previously unknown flowering plant family,” said Hermsen. “However, it is also possible that Cavilignum is related to a modern plant species, but we just do not yet have enough information to make the connection.”

The species name, pratchettii, is in honor of the late British fantasy author Sir Terry Pratchett, a decision that came from the first author of the study, Caroline Siegert of the Department of Environmental and Plant Biology at Ohio University.

“I have been a fan of his work since I was a child and grew up alongside one of his main characters, Tiffany Aching,” Siegert explained. “It felt like a fitting tribute to an amazing man who inspired me to be brave and intelligent with the characters he created.”

Both new plants add to a developing picture of the Gray Fossil Site as an ancient ecosystem full of surprises. As researchers continue to study the extinct plants and animals of the site, they piece together the story of how this part of the world has changed through time, and how Appalachian life has responded.