A petrified tree that Dr. Seuss might have invented

In the ancient prehistory of Earth, there is a chapter waiting to be told known as Romer's Rift. Researchers have identified a gap in the tetrapod fossil record between 360 million and 345 million years ago, after fish began adapting to land and more than 80 million years before the first dinosaurs.

While mysteries remain about evolution's experiments on living things during that 15-million-year period, a fossilized tree described in a new paper offers more insight into some of what happened in the laboratory during this period. nature happened.

Called Sanfordiacaulis densifolia, the tree had a diameter of six inches and an almost three-foot-high trunk that was not made of wood, but of vascular plant material, such as ferns. The crown had more than 200 finely striped, compound leaves that emerged from spiral-patterned branches that extended 21 feet outward. Robert Gastaldo, professor of geology at Colby College in Maine and author of the study published Friday in the journal Current Biology, likened it to “an upside-down toilet brush.” Comically top-heavy, even Seussian, the tree most likely stayed upright by interweaving its branches with those of neighboring trees.

“This is a completely new and different kind of plant” than was found in the late Paleozoic, says Patricia Gensel, professor of biology at the University of North Carolina at Chapel Hill and another author of the paper. She added: “We normally get bits and pieces of plants, or mineralized logs, from Romer's Gap. We don't have many whole plants that we can reconstruct. We can do this.”

The tree was excavated near Valley Waters, New Brunswick, in an active private quarry in Canada Stonehammer UNESCO Global Geopark. (A new fossil museum will open in the village later this year.) The area is part of the 350-million-year-old Albert Formation, a geological layer that has also yielded fossilized fish and trace fossils. Although partial fossils of the same tree species had previously been found, the new discovery represents the only fossil whose trunk and crown have been preserved together.

“It is very rare to find something so well preserved and unique,” ​​said Matt Stimson, an author of the study who is working on the New Brunswick Museum and who unearthed S. densifolia for the first time with his colleague Olivia King. “It's like finding a cactus in the middle of a Canadian boreal forest.”

Trees with spongy trunks 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 tree fossils from 398 million years to 327 million years ago, and have only been found in coastal wetlands.

The Valley Waters quarry was once a swampy, tropical ecosystem surrounding a rift lake, a deep body of water flowing atop a fault zone. The sediments were similar to those of modern-day Lake Victoria and Lake Tanganyika in East Africa. The bank containing the tree was swept away during a catastrophic earthquake, leaving the tree on its side at the bottom of the lake. The subsequent mudslides quickly buried vegetation and destroyed aquatic life. Sediments have filled in around the leaves, preserving the specimen three-dimensionally, which falls somewhere on the evolutionary continuum between a woody tree and a huge plant.

S. densifolia evolved at a time when the layered structure of the forest was still developing and the plants were diversifying, Ms King said. It probably lived under the tallest trees, such as the more than 30 meters high, scaly bark Lepidodendronbut staying low above lycopods and mosses.

“The architecture of this tree suggests that it grew into an ecological niche in which it sat in the center of the canopy, trying to capture as much sunlight as possible with branches that extended almost as long as the tree was tall,” said Mrs. King.

“It's an experiment in plant biology that was successful for a while, but then it wasn't anymore,” said Dr. Gastaldo. “We don't see anything like it in the forests we've been able to evaluate since then.”