The Argentine fossils carry the history of the beech and beech family far away in the southern hemisphere

One of the most important plant families in the world has a history that extends much further south than any other living or fossil specimen previously listed, as shown by fruit fossils and chinquapin leaves uncovered in Patagonia, Argentina, according to the researchers.

"The oak and beech family is widely recognized as one of the most important plant groups and has always been considered northern," said Peter Wilf, professor of geoscience and associate at Penn's Earth and Environmental Systems Institute. State. "We add a huge spatial dimension to the history of the Fagaceae family, and it's exciting." The plant family also includes closely related chestnuts and chinquapins.

Communes in the northern hemisphere and the Asian tropics, Fagaceae only cross the equator in Southeast Asia and even hardly. The latest study published today (June 7) in Science, extends the biogeographic history of the family and suggests a legacy of the Gondwana supercontinent in Asia's larger tropical forests than expected.

The researchers first found fossils resembling oak leaves, with straight secondary veins and a secondary vein tooth, in Laguna del Hunco, Chubut province. The leaves represent about 10% of the thousands of leaf fossils dating back 52 million years, representing nearly 200 species found on the site for two decades as part of a long-term project between Penn State. , Cornell University and the Museo Paleontológico Egidio Feruglio (MEF), Trelew, Argentina.

For years, researchers have been reluctant to categorize the leaves, as paleobotanist Edward Berry has attributed similar fossils to another family, and any claim to Fagaceae in such a remote place would require evidence to support.

Later, the team uncovered rare fruit fossils – two bunches of fruit, including one with over 110 immature fruits – on the site and compared them to living relatives. They discovered that it was fossils of the ancient Castanopsis, an Asian chinquapin that today dominates the tropical rainforest of the diversity and low altitude of the island. South East Asia.

"One of the first clues was a little ledge where the fruit is cracking," Wilf said. "I recognized this lip as being similar to the Japanese chinquapin fruit, and then realized that there was a nut inside."

The nuts are fully enclosed in a squamous outer shell, or cup, which splits when the fruits ripen. The cups are arranged on a post-shaped fruiting axis and the young nuts retain delicate parts as soon as they flower. Wilf stated that their characteristics resemble those of living Castanopsis, and that the fruits confirm that the leaves are Fagaceae.

"This is the first confirmed evidence that Fagaceae, considered to be limited to the northern hemisphere, was found in the southern hemisphere," said Maria Gandolfo, associate professor at the University of California. Cornell University. "It's remarkable and allows us to rethink the origins of fossil flora."

Fossils date back to the beginning of the Eocene 52.2 million years ago. These are the only living or fossilized Fagaceae ever found south of the Malay Archipelago, the chain of islands just north of Australia.

At the beginning of the Eocene, where it was hot, there was no polar ice, and South America, Antarctica and Australia did not occur. were not completely separated, constituting the final stage of the Gondwana supercontinent. Researchers believe that animals helped disperse the ancestors of Chinquapin from North America to South America in an earlier era. Plants thrived in Patagonia's wet rainforest, whose closest modern analogue is the rainforest mountain in New Guinea.

"Before the current semi-desert conditions, trees covered Patagonia," said Rubén Cúneo, director of the MEF. "The changing climatic conditions have turned it into a shrub and the trees have been moved."

The chinquapins could also have gone to the then Antarctic and Australia, said Wilf. Castanopsis may have survived in Australia until the continent collided with Southeast Asia, where chinquapins are nowadays essential species, providing the structure of the forest. , as well as the food and habitat of birds, insects and mammals.

"We find 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," Wilf said. "You can find some of the associations with Castanopsis observed in Eocene Argentina up to the south of China and beyond."

Today, Castanopsis plays an important role in the interception of mountain rains throughout the year, which provide drinking water for more than half a billion of people, drinking water and fishing, and maintains various coastal and freshwater ecosystems. However, humans are clearing these tropical forests for timber, development and crops, and modern climate change is increasing droughts and the frequency of fires.

"These plants are adaptable if given time and space," said Wilf, adding that the Castanopsis journey between Patagonia and Southeast Asia has unfolded on millions of years and thousands of kilometers. "But the pace of change is now hundreds of times faster than in geological time, and the animals that depend on these plants are adaptable only to the extent that they are, and we are the only one in the world. One of the animals that depend on this system If we lose very quickly reliable water flows for agriculture, the cleanliness of coral reefs off the coast, biodiversity and so much more. "

This study has implications for extinction in the face of climate change, according to Kevin Nixon, professor and curator for L.H. Bailey Hortorium, of Cornell University. He added that Castanopsis was extinct in Patagonia because of a major extinction caused by the slow cooling and drying of the climate that had occurred during the Antarctic ice age and of the rise of the Andes.

"This kind of climate change can have huge effects on biodiversity," said Nixon. "The relevance of understanding this is that we can begin to look at the processes of extinction, the more we can understand the causes of extinction, the better we can deal with it."