The castanopsis fossil Peter Wilf, Penn State University

Fossils found deep in the forests of Argentina suggest that relatives of oak trees evolved in the southern hemisphere, not the north as previously thought.

Fagaceae are one of the most important groups of flowering plants including oaks and beeches, and its trees are a cornerstone of rainforests across south-east Asia. The family’s extensive fossil record has only been found in the northern hemisphere before. But a pair of 52 million-year old fossils discovered in Laguna del Hunco, in Argentine Patagonia, has led researchers to a hypothesis that one genus in the family started life in the south.

Since work started in Patagonia’s Laguna del Hunco in 1999, researchers have found hundreds of leaf fossils that looked like Fagaceae members but were not considered evidence enough alone. However, suspicions were confirmed when an international team found two specimens in the area covered in fruits and little flower parts of the Castanopsis genus. “That was when the evidence really became overwhelming,” says Peter Wilf of Pennsylvania State University. His team were “pretty shocked” because the nearest fossils in Castanopsis were found 8000 miles away in New Guinea.


The fossils are the oldest in the genus by about 8 million years, and date back to the the Eocene, before Earth’s land masses split, enabling them to spread to modern day continents of the north.

The idea of southern roots for some Fagaceae species means researchers will now begin hunting for the fossils of other members of the family in previously unsuspected places, which could shed light on how other shrubs and trees evolved. Mark Chase of Kew Gardens says the research shows Fagaceae “were in the past much more diverse than at present, particularly on the continents now in the southern hemisphere, in which they are absent today.”

The finding also has ramifications for the conservation of tree species in south-east Asia, where today extinction and deforestation rates are the highest in the world. “Paleontology [the study of fossil animals and plants] informs conservation, and is widely used as a basis for conservation around the world, by showing us the origins and environmental histories of living plants and animals,” says Wilf.

Journal reference: Science, DOI: 10.1126/science.aaw5139