The prehistoric tree is the first of its kind found under the equator

Millions of years ago, a volcano erupted in the Patagonian region of southern Argentina, leaving behind a huge caldera. The water accumulated in the crater and eventually became a lake teeming with innumerable plants, insects and other life forms. Over time, these creatures fossilized deep into the mud and ash layers of the lake, creating a kind of geological jackpot for paleontologists today.

Today, the ancient lake has delivered a particularly exciting treasure: fossils of a 52 million year old tree, the first of its kind found in the southern hemisphere, suggesting that the plant has evolved there.

The site's fruit and leaf fossils, called Laguna del Hunco, belong to a still-alive kind of tree called Castanopsisor chinquapin, which is found today largely in mountain rainforests in Southeast Asia. Castanopsis is very similar to his close relative Castanea, or chestnut, producing edible nuts and "incredible and showy flower peaks," says Peter Wilf, paleobotanist from Penn State, a member of the team that describes today 's discovery in the newspaper Science.

This discovery helps scientists better understand the life story of a group of plants of economic and ecological importance: Castanopsis is part of Fagaceae, a family of flowering plants that also includes beeches and oaks.

"These are the trees that define the structure of the forest throughout the northern hemisphere and in the Asian tropics. They are absolutely dominant, "says Wilf, who led the research in collaboration with Cornell University and the Paleontological Museum Egidio Feruglio. As a source of wood, these trees are also a "focal point of the food web," says Wilf, providing nutrition not only to rodents, but also to humans and other mammals, as well as to birds and insects.

"I am heartened to see their importance in the Paleo archives because they are already ecologically and economically critical," says tree biologist Meg Lowman in an e-mail. Lowman, who did not participate in the study, is also an explorer of National Geographic and the director of the Tree Foundation, a nonprofit organization.

So, what is a tree in the virgin forest of Southeast Asia in Patagonia? The answer lies in changing climates and continents.

When the fossils of the lake formed, the world was in the Eocene era, a warm period during which South America, Antarctica and Australia were still close to each other, just before the breakup of the lake. former southern supercontinent, Gondwana. The region that is now cold and dry in Patagonia was a cool and wet rainforest. This climate is similar to the current mountains of Borneo and New Guinea, the closest places to Laguna del Hunco where Castanopsis grows today, and are 8,000 miles from the site.

"This study highlights the importance of Fagaceae, already well-documented for their roles both economically and ecologically, as a key link in Gondwana's botanical archives, "says Lowman.

After all, finding fossils so far from the current habitat of trees tells a story of survival that spans several millennia.

"These plants have survived global climate change, the break-up of Gondwana, the movement of continents over tens of millions of years – they have followed their preferred habitat," Wilf said. Of course, the hope is that the story does not end with their impending extinction. While human activities such as deforestation continue rapidly, Castanopsis is now threatened, notes Wilf.

"They can not adapt. They have neither the time nor the space to adapt to geological time, "he says. But these kinds of discoveries can educate the public and inspire conservation efforts, says Wilf, who has been digging in Laguna del Hunco for 20 years and plans to continue working there.

"Paleontology informs conservation," he says. "We are beginning to see the ancient history of these habitats and how important it is to maintain them because they can not come back if we lose them."