An Ancient Tree Leads to New Understanding
A tree fossil that Colby researchers helped interpret enriches our perspective of a mysterious period in Earth’s past
In December 2017, Robert Gastaldo’s phone rang. Two graduate students in Canada had just discovered a strange-looking fossil of a tree in a quarry, on land that, hundreds of millions of years ago, had been at the bottom of a deep lake. This ancient tree had lived around 350 million years ago, 100 million years before the first dinosaurs, and it looked like nothing that either of them had ever seen.
The geology researchers, Olivia King and Matthew Stimson, from Saint Mary’s University in Halifax, had heard Gastaldo was the person to speak to. Could he come and help them figure out what it was?
Gastaldo, Colby’s Whipple-Coddington Professor of Geology, Emeritus, started his car and drove the five hours from Waterville to New Brunswick. With him was Ian Glasspool, a postdoctoral fellow in geology at Colby. When they arrived and stood in a storage unit in front of a 7-by-7-foot block of sandstone and siltstone, they were stunned.
“As soon as I saw it,” said Glasspool, “I knew I was unlikely to see anything like it ever again. … It is profoundly different” from any other tree we know existed.
Gastaldo announced the discovery with his colleagues in a coauthored paper published in February in Current Biology. Since then, the news has generated worldwide interest, placing the sciences at Colby firmly at the center of one the year’s most intriguing science stories.
The tree stood almost 10 feet tall. Its trunk was made not of wood, which would take another 10 million years to evolve, but of vascular tissue, like fern stems, and it was thin: only 6 inches in diameter. At the top were 250 remarkably long leaves. Gastaldo estimated that the leaves extended at least 18 feet from the skinny trunk, which made it perilously top heavy.
The tree, which the researchers named Sanfordiacaulis densifolia after the quarry’s owner, Laurie Sanford, looked like it came from a surrealistic dream world. In Gastaldo’s eyes, it resembled an upside-down toilet brush. “We still ponder how the thing even stood up,” said Gastaldo. “The weight of the leaves in the crown must have made it unstable—you would think it would have tipped over at the slightest gust of wind.”
The discovery illuminates a distant chapter in the deep history of life. The tree grew during a subdivision of the late Paleozoic era, between approximately 360 million and 320 million years ago. During this period, fish had only just started to adapt to land. But it was also a time of transition and evolutionary experimentation in the plant kingdom. An array of weird life forms emerged, lasting only a short time before they disappeared. “We were getting many different experimental plant forms,” said Gastaldo. “Some things were successful, and others were not.” Sanfordiacaulis densifolia probably flourished for several million years, but its top-heavy structure would have been its weak point. It was eventually outcompeted by more efficient plants, some of which were the ancestors of contemporary trees.
This specimen of Sanfordiacaulis densifolia was only preserved because it happened to grow on the edge of a deep rift lake. A large earthquake caused the lake to swallow up the surrounding land, and the tree sank to the bottom. The low-oxygen environment in the depths allowed it to be preserved.
For Gastaldo and his team, the tree was difficult to place in relation to other known plants. It resembled a gymnosperm, the plant family that includes pines and firs. But it was strange in some important ways. Gymnosperms have seeds. Sanfordiacaulis densifolia, though, propagated itself with spores.
It also looked like an absurdist palm tree—but it had nothing to do with palms, which didn’t evolve for another 110 million years. It was a completely new kind of plant. “To find this tree that has no analog, no relative that’s similar—that is extremely unusual,” said Gastaldo.
Paleobotanists almost never uncover entire trees from this era. Across a fossil record that spans hundreds of millions of years, there are only a handful of trees with the crown still attached. Sanfordiacaulis densifolia is the only direct evidence we have of a plant that occupied the subcanopy level of the forest, just below the main canopy.
Since the discovery in 2017, Gastaldo, Glasspool, and their colleagues, including King and Stimson and researchers in Canada, North Carolina, and the United Kingdom, have been busy analyzing the fossil. To reconstruct what the tree would have looked like, they turned to Tim Stonesifer, Colby’s assistant director for media technology. He designed a digital 3D reconstruction of the unique plant, which was published in the paper and reproduced in press coverage, in outlets including the New York Times and CNN
“I love that my work at Colby has an impact on a lot of students and faculty,” said Stonesifer. “But it was really rewarding to see these images reach a wider audience. I took a lot of pride in that.”
The team also returned to the quarry, where they uncovered four other examples of the same tree nearby. They now hope to excavate even deeper to reveal the root systems.
Gastaldo can barely believe their luck. During the Paleozoic, much of North America was covered by a warm sea, and less than one percent of what is now exposed rock was land 350 million years ago. The chance of finding a single Sanfordiacaulis densifolia was miniscule. Gastaldo and his team found five.
“We should all go out now,” said Gastaldo, “and buy lottery tickets.”
