Trilobites: Tomatillo Fossils, 52 Million Years Old, Are Discovered in Patagonia

Trilobites
By NICHOLAS ST. FLEUR

The nightshades have an ominous reputation, but this large plant family is more than just its most poisonous members, like belladonna. It contains more than 2,400 different species, including some of the most widely consumed fruits and vegetables in the world, such as potatoes, tomatoes and peppers.

By analyzing the fossil record through molecular data, scientists had estimated that the nightshade family was about 30 million years old, making it a relatively young plant family. But paleontologists in the Patagonia region in Argentina have discovered 52 million-year-old fossilized tomatillos, which are also nightshades. The discovery could push the age of the entire plant family, perhaps, back to when dinosaurs roamed the Earth.

Tomatillos are like the tomato’s oddball cousin. They are small, green and covered in a papery husk, which makes them look like Chinese lanterns. The berry beneath the sheath is the key ingredient in a tangy, zesty salsa verde. Until now, researchers thought tomatillos first evolved about 10 million years ago. But the new findings suggest that the fruits are actually five times that old. Because tomatillos are thought to be an evolutionarily young member of the nightshade group, the recent finding suggests that the entire family may be much older than scientists had previously estimated.

“The finding of the fossils extends the origins of these plants for at least 25 million more years,” said Rubèn Cunéo, the director of Museo Paleontológico Egidio Feruglio in Argentina and an author of a paper on the discovery published Thursday in the journal Science. “Now we have a much better idea of the evolution of this incredible group of plants that are so important from an economic viewpoint in the modern world.”

Peter Wilf, a paleobotanist from Pennsylvania State University and the paper’s lead author, collected the two fossils in 2002 and 2006 while exploring a site at Laguna del Hunco in Chubut Province, Argentina, with a team of researchers. Millions of years ago, the area was near a lake that had been formed in a volcano’s caldera and was surrounded by rainforest and teeming with prehistoric life. Now the remnants of those prehistoric plants and animals are preserved in the endless dry and desolate hills.

“There are white rocks that are jam-packed full of fossils, so many fossils that people cry when they see them,” Dr. Wilf said. “I’ve never seen so many beautiful fossils in one place.”

To determine what the fossil was, he and his team compared it with more than 100 living nightshade species as well as several plants outside of the family. It was through careful morphological analysis that the team determined that the fossils belonged to a newly discovered species of tomatillo, within the nightshade family.

He said that when he first saw the fossils he was surprised that the plant’s delicate husks had been preserved, that the veins on the husks were visible and that the berry, now black and turned to coal, was also present. He and his team named it Physalis infinemundi. No other fossilized fruit from the nightshade family had ever been found before, Dr. Wilf said. Only fossilized seeds had told the story of the family’s evolutionary history.

“The initial discovery was a very big O.M.G. moment,” he said. “I was like, ‘Wait a minute, wait a minute, wait a minute. Could it be? Could it be? Could it be? Really? Really? Really?’ Then I just went nuts.”

He said the findings suggested that the nightshade family originated much earlier than previously thought, and that it was well diversified during a time when South America was attached to Antarctica and Australia as the supercontinent Gondwana. It also shows that tomatillos had husks millions of years ago, which he said could have helped shield the berries from rain and kept them afloat if they fell into the water.

“This is an outstanding advancement in our understanding of the history of the tomato and potato family,” Steven R. Manchester, a curator of paleobotany at the Florida Museum of Natural History in Gainesville, said in an email. He said the fossils appear to share the same unique features of the tomatillo genus Physalis. “As it matches this living genus so perfectly, its position as a member of the nightshade/tomato family is quite secure.”

Tiina Sarkinen, a molecular biologist and plant taxonomist from the Royal Botanic Garden Edinburgh said in an email that the fossils clearly showed that the nightshade family existed 52 million years ago. But she said it was still possible that the fossils were an earlier, diverging relative of the tomatillo genus, related to the group but not a member of it.

“Whether the fossils truly are an extinct relative of the tomatillo is the big question,” she said. “It is exciting to think this is a past relative of what we now eat in our salsas.”