Grapes have played an important role in human history for thousands of years, forming the basis for the wines our ancestors made thousands of years ago. But that might not have been the case if the dinosaurs hadn't disappeared from the face of the earth, new research suggests.
When an asteroid struck Earth 66 million years ago, it wiped out the huge, lumbering animals, creating the opportunity for other creatures and plants to thrive.
Now, the discovery of fossilized grape seeds in Colombia, Panama and Peru, ranging from 19 million to 60 million years old, is shedding light on how these humble fruits took hold in Earth's dense forests and eventually established a global presence. One of the newly discovered seeds is the oldest example of a plant in the grape family found in the Western Hemisphere, according to a study of the specimens published Monday in the journal Nature Plants.
"These are the oldest grapes ever found in this part of the world, and they're a few million years younger than the oldest ones ever found on the other side of the planet," lead study author Fabiany Herrera, assistant curator of paleobotany at the Field Museum at the Negaunee Integrative Research Center in Chicago, said in a statement. "This discovery is important because it shows that grapes really started spreading around the world after the dinosaurs went extinct."
Like the soft tissues of animals, true fruits don't preserve well in the fossil record. But seeds, which fossilize earlier, can help scientists understand what plants were present at different stages in Earth's history as they reconstruct the tree of life and establish origin stories.
The oldest grape seed fossils found so far were excavated in India and date back 66 million years, around the time the dinosaurs became extinct.
"We always think about the animals, the dinosaurs, because they were the ones that were affected the most, but the extinction also had a huge impact on plants," Herrera said. "The forest reset itself in a way that changed the composition of the plants."
A difficult search
Herrera's PhD advisor, Steven Manchester, who is also a senior author on the new study, published a paper on the grape fossils found in India. It inspired Herrera to wonder where other grape seed fossils might exist, such as in South America, even though they had never been found there.
"Grapes have an extensive fossil record that starts about 50 million years ago, so I wanted to discover one in South America, but it was like looking for a needle in a haystack," Herrera said. "I've been looking for the oldest grape in the Western Hemisphere since I was an undergraduate."
Herrera and study co-author Mónica Carvalho, an assistant curator at the University of Michigan Museum of Paleontology, were doing fieldwork in the Colombian Andes in 2022 when Carvalho discovered a fossil. It turned out to be a 60-million-year-old grape seed fossil trapped in rock, one of the oldest in the world and the first found in South America.
"She looked at me and said, 'Fabiany, a grape!' And then I looked at it and I was like, 'Oh my God.' It was so exciting," Herrera said.
Although the fossil was small, its shape, size and other features helped the duo identify it as a grape seed. And back in the lab, the researchers performed CT scans to study its internal structure and confirm their findings.
They named the newly discovered species Lithouva susmanii, or "Susman's stone grape," in honor of Arthur T. Susman, a pioneer of South American paleobotany at the Field Museum.
"This new species is also important because it supports the South American origin of the group from which the common grape genus Vitis evolved," said study co-author Gregory Stull of the National Museum of Natural History.
The rocks were deposited in ancient lakes, rivers and coastal areas, Herrera said.
"To find such small seeds, I split every piece of rock available in the field," he said, adding that the difficult search "is the fun part of my job as a paleobotanist."
Encouraged by their find, the team conducted more fieldwork in South and Central America, finding nine new species of fossil grape seeds trapped in sedimentary rocks. And by tracing the lineage of the ancient seeds to their modern grape counterparts, the team realized that something had allowed the plants to thrive and spread.
How ancient forests changed
The team hypothesized that when the dinosaurs went extinct, their absence changed the entire structure of the forests.
"Large animals, like dinosaurs, are known to change their surrounding ecosystems. We think that if large dinosaurs were roaming the forest, they would probably knock down trees, leaving forests more open than they are today," Carvalho said.
After the dinosaurs disappeared, tropical forests became overgrown and layers of trees created an undergrowth and canopy. These dense forests made it difficult for plants to receive light and they had to compete with each other for resources. And climbing plants had an advantage and used it to reach the canopy, the researchers said.
"In the fossil record around this time, we start seeing more plants that use vines to climb trees, like grapes," Herrera said.
Meanwhile, various birds and mammals began to populate the Earth after the dinosaurs disappeared. They probably also contributed to the spread of grape seeds.
The resilience of plants
Studying the seeds tells the story of how grapes spread, adapted, and became extinct over thousands of years. It shows how well the grape species survived in other parts of the world, despite disappearing from Central and South America over time.
Several fossils are related to modern grapes, and others are distant relatives or grapes native to the Western Hemisphere. For example, some of the fossil species can be traced back to grapes that are now found only in Asia and Africa, but it is unclear why grapes became extinct in Central and South America, Herrera said.
"The new fossil species tell us a tumultuous and complex history," he said. "We usually think of the diverse and modern rainforests as a 'museum' model, where all the species accumulate over time. But our study shows that extinctions have been a major factor in the evolution of rainforests. Now we need to identify what caused those extinctions over the past 60 million years."
Herrera wants to look for other examples of fossil plants, such as sunflowers, orchids and pineapples, to see if they once lived in tropical forests.
By studying the origins and past adaptations of plants, scientists can better understand how they are faring during the climate crisis.
"I just hope that most living plant seeds adapt quickly to the current climate crisis. The fossil record of seeds tells us that plants are resilient, but they can also disappear completely from an entire continent," Herrera said.
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