In Earth’s ancient prehistory, there is a chapter waiting to be told known as Romer’s Gap. The researchers identified a break in the tetrapod fossil record between 360 and 345 million years ago, after fish had begun to adapt to land and more than 80 million years before the first dinosaurs.
While mysteries remain about evolution’s experiments with living things during that 15-million-year gap, a fossilized tree described in a new paper offers more insight into some of what was going on during that time in her lab. nature.
It was named Sanfordiacaulis densifolia, the tree was six inches in diameter with a nearly 10-foot-tall trunk composed not of wood but of vascular plant material such as ferns. Its crown had more than 200 finely ribbed, compound leaves that came from spirally patterned branches that radiated 2½ feet outward. Robert Gastaldo, a geology professor at Colby College in Maine who authored the study, which was published Friday in the journal Current Biology, compared it to an “upside-down toilet brush.” Comically towering, even Seussian, the tree likely remained upright, entangling its branches with those of neighboring trees.
“This is a completely new and different kind of plant” from what had been found in the Late Paleozoic Era, said Patricia Gensel, a professor of biology at the University of North Carolina at Chapel Hill and another author of the paper. He added, “Typically we get pieces of plants or mineralized tree trunks from Romer’s Gap. We don’t have many whole plants that we can reconstruct. We can do that.”
The tree was discovered near Valley Waters, New Brunswick, in an active private quarry in Canada’s Stonehammer UNESCO World Geopark. (A new fossil museum will open in the village later this year.) The site is part of the 350-million-year-old Albert Formation, a geological layer that has also yielded fossil fish and trace fossils. Although a few fossils of the same tree species had previously been found, the new discovery represents the only such fossil whose trunk and crown were preserved together.
“It’s very rare to find something this well-preserved and unique,” said study author Matt Stimson, who works at the New Brunswick Museum and who first excavated S. densifolia with another study author, Olivia King of Saint Mary’s University. “It’s like finding a cactus in the middle of a Canadian boreal forest.”
Trees with spongy trunks made of vascular tissue first appeared 393 million to 383 million years ago. Their woody counterparts entered the fossil record about 10 million years later. Trunks and stumps make up the bulk of arboreal fossils from 398 million years to 327 million years ago, and have only been found in coastal wetland areas.
The quarry at Valley Waters was once a swampy, tropical ecosystem surrounding a rift lake, a deep body of water that ran atop a fault zone. Its sediments were similar to those of modern Lake Victoria and Tanganyika in East Africa. The bank containing the tree was removed during a devastating earthquake, depositing the tree on its side at the bottom of the lake. The landslides that followed quickly buried the vegetation and wiped out the aquatic life. Sediment fills in around the leaves, preserving the specimen in three dimensions, which falls somewhere on the evolutionary continuum between a woody tree and a giant plant.
S. densifolia grew at a time when the stepped canopy forest structure was still developing and plants were diversifying, Ms King said. It probably lived under the tallest trees, such as the 100-plus-foot-tall scaly lepidodendron, but above lycopods and low-growing mosses.
“The architecture of this tree suggests that it was growing in this ecological niche of being in the mid-canopy, trying to capture as much sunlight as possible with branches that stretched almost as high as the tree was tall,” Ms King said.
“It’s an experiment in plant biology that was successful for a while, and then it wasn’t,” Dr. Gastaldo said. “We don’t see anything like this in any of the forests we’ve been able to assess since then.”
