June 7 (UPI) -- Researchers have unearthed a collection of chinquapin fruit and leaf fossils in Patagonia that suggests the oak and beech family, one of the most important plant families, has evolutionary roots in the Southern Hemisphere.
"The oak and beech family is recognized everywhere as one of the most important plant groups and has always been considered northern," Peter Wilf, professor of geosciences at Pennsylvania State University, said in a news release. "We're adding a huge spatial dimension to the history of the Fagaceae family, and that's exciting."
Plant species belonging to the Fagaceae family are common throughout the Northern Hemisphere. The only members known to grow on the other side of the equator are found in Southeast Asia.
But new analysis suggests the family once extended much farther into the Southern Hemisphere. The tropical forests of Asia, researchers estimate, once stretched across thousands of miles across the Gondwanan supercontinent.
Scientists discovered oak-like leaves among the thousands of leaf fossils recovered from Laguna del Hunco, a dig site in Argentina's Chubut province. Researchers from the U.S. and Argentina have been excavating ancient plant fossils at the site for nearly two decades.
The newly identified oak-like leaves feature straight secondary veins and one tooth per secondary vein. Scientists also found fossilized fruits belonging to Castanopsis, an Asian evergreen genus. Today, Castanopsis species dominate the low elevation mountain rainforests of Southeast Asia.
"One of the first clues was a little lip where the fruit is splitting open," Wilf said. "I recognized this lip as being similar to the fruit of the Japanese chinquapin. Then I realized there's a nut inside."
The new findings -- published this week in the journal Science -- suggest modern Castanopsis species trace their evolutionary origins to the Southern Hemisphere, and that during the Eocene, 52.2 million years ago, beech and oak relatives proliferated throughout the Southern Hemisphere.
"We're finding, in the same rocks as Castanopsis, fossils of many other plants that live with it today in New Guinea and elsewhere, including ferns, conifers and flowering plants," said Wilf. "You can trace some of the associations with Castanopsis seen in Eocene Argentina to southern China and beyond."
Oak and beech ancestors disappeared from Patagonia millions of years ago as a result of climate change. Though adaptable, the ancient plant family requires time and space to adjust. Today, climate change is happening at a rapid pace.
"Those kinds of climate changes can have massive effects on biodiversity," said Kevin Nixon, a professor of plant biology at Cornell University. "The relevance of understanding this is we can start to look at extinction processes. The better we can understand what causes extinction, the better we can deal with it."