Fossil Rainforests of Patagonia: Ancient Biodiversity and Living Legacy

Erin Dugan, Research Unplugged Intern
April 13, 2010

Peter Wilf was the fourth speaker in this season's Research Unplugged conversation series last Wednesday, April 7th at the Penn State Downtown Theatre. Wilf, associate professor of geosciences, spoke about his ongoing project in Patagonia, Argentina—located on the southern tip of South America—where he and his colleagues have discovered eight thousand plant fossil specimens from hundreds of species, evidence of the ancient biodiversity that once existed.

man in green shirt and hat smiles in front of mountains

Peter Wilf on Mt. Baldy above Alta, Utah

"The last time our world was in a great greenhouse stage was 50 million years ago," explained Wilf to the large crowd in attendance, including a group from The Village at Penn State retirement community.

"To some geologists, this seems like yesterday," noted Wilf. "Although they are vastly different today, millions of years ago, Antarctica, Australia, and South America had very similar ecosystems because they used to be connected."

Animal remains have also led researchers to believe that these continents were connected. "Researchers found 61 million-year-old teeth in Patagonia, and later identified them as close relatives of the platypus, a quintessentially Australian animal today," Wilf said. "This demonstrates the southern connection of biota across Antarctica that we also see in the Patagonian fossil plants."

"In the field of paleobotany, our best friend is volcanic ash found associated with our fossils. When volcanoes explode the radioactive clocks in the minerals formed at eruption time start ticking. When we date those minerals we get an eruption age, which we can then correlate to our fossils," he explained.

Once you have some clues as to where to dig, you need to clear the rock— hard sandstone mixed with volcanic ash—to reach the fossils. Explained Wilf, during excavation, "there are moments of silence, and then shouts of joy, as someone discovers something; then more moments of silence and rarely a curse or two when something doesn't go as planned."

Showing the audience his slides of the dig site at Laguna del Hunco, Wilf joked, "Just another day in the office." Of the eight thousand plant fossil specimens that he and his colleagues discovered, they have been able to identify four thousand of them. Noted Wilf, "Paleobotany involves using morphological characteristics, among other factors, to group the fossils. From our specimens, we can tell what family of plants they belong in, and sometimes the genus." Each specimen of fruits, seeds, leaves, or flowers is first categorized in a morphological group and then botanically studied, he explained.

Wilf showed many photos of his group's extremely well-preserved plant fossil specimens of lineages that now live in the Australasian rainforest region, including Eucalyptus (gum tree), Gymnostoma (a small rainforest tree), and conifers such as Agathis (kauri, a forest giant) and Dacrycarpus (kahikatea). "Once you find something like this, you have to do it again—that's why I'm in the business!" he said.

The highly diverse modern rainforests where these plant genera now live, in places like Australia, New Guinea, New Caledonia, and New Zealand, provide a wealth of information that helps to reconstruct the ancient environment. "The array of plant fossils that we've found in Patagonia is a great example of a very diverse ecosystem that is now completely gone from the region due to climate change and extinction, but it has left a living legacy dispersed among southern rainforest environments that are many thousands of miles away from the fossil site."

For more about Peter Wilf, read on...

Last Updated April 13, 2010