A study led by experts from the University of Bologna pointed out in 2022 that the scientific community has so far counted 73,300 different species of trees and that it is estimated that there may be another 9,000 that have not yet been identified and studied in detail. The common definition of a tree is that of a plant, with a woody stem, that branches at a certain height from the ground. Despite this great variety of species, we all have an idea of what trees are like.
Our notion must now be expanded taking into account the discovery and study of fossil remains of a type of tree never seen in person by humans, a variety very different from the one we knew until now, as explained by the authors of the discovery in an article published in Current Biology magazine (February 2).
In the fossil record, trees are typically preserved with only their trunks. They typically do not include sheets to show what their canopies and general shapes looked like, the study authors explain to contextualize their discovery. The novelty in their work is that they have been able to locate fossils of primitive trees in New Brunswick, Canada, "with a surprising and unique three-dimensional crown shape." The new tree species has been given the scientific name Sanfordiacaulis densifolia.
"It is surprising how this tree produced enormously long leaves around its stretched trunk and without low branches," says Robert Gastaldo, a researcher at Colby College in Waterville (Maine, United States), and first signatory of the study.
The shapes adopted by these 350 million-year-old trees resemble those of a fern or a palm tree, although palm trees (which are not trees) did not emerge until 300 million years later, Gastaldo explains. However, the functional leaves of ferns or palm trees look similar because they group their leaves at the top.
“On the other hand, Sanfordiacaulis preserves more than 250 leaves around its trunk, and each partially preserved leaf extends 1.75 meters from it,” indicates Robert Gastaldo in a note released by his university. “We estimate that each leaf grew at least another meter before we were finished. This means that the 'bottle brush' had a dense canopy of leaves that extended at least 5.5 meters (or 18 feet) around a trunk that was non-woody and only 16 centimeters (or 0.5 feet) in diameter. . Surprising to say the least.”
This work was made possible through a long-term international collaboration with Matthew Stimson and Olivia King of the New Brunswick Museum, Saint John, and Saint Mary's University in Halifax. The researchers' findings offer important information about the evolution of plants and arborescence, which means plants that grow to the height of a tree, or at least 15 feet at maturity. They are also a reminder that throughout the history of life on Earth, there have been trees unlike any we have seen before and some that seem to have sprung from the imagination of Dr. Seuss [pseudonym of Theodor Seuss Geisel, American writer and cartoonist, known for his children's books], say the researchers.
“We all have a mental concept of what a tree is like, depending on where we live on the planet, and we have a vision of what is familiar to us,” says Gastaldo. “The fossil we report on is unique and a rare form of growth in the history of life. It is one of the experiments in evolution during a time when forest plants underwent biodiversification, and it is a form that appears to be short-lived.
The fossils in question were preserved through the catastrophic earthquake-induced burial of trees and other vegetation along the margin of a lake. The first fossil tree was unearthed about 7 years ago in a quarry, but it only included a partial sample. Several years passed until four other specimens of the same plant were found, very close spatially, says Gastaldo.
One of the specimens revealed how the leaves started from the top of the tree, which makes it “absolutely unique.” It is one of the few in a fossil record spanning more than 400 million years in which a trunk is preserved around which the crown leaves are still attached, researchers say.
"Any fossil tree with an intact crown is a rarity in the history of life," says Gastaldo. “Having the crown leaves attached to a trunk, in itself, raises the question of what type of plant it is, how that plant is organized, and whether it is some form that continues to the present, or is outside the 'normal' concept. '. from a tree? All of these questions, and more, led to this multi-year effort.”
The researchers report that the tree likely relied on its unusual growth form to maximize the amount of light it could capture and reduce its competition with other plants on the ground. They suggest the tree now represents the earliest evidence of smaller trees growing under a higher forest canopy. It means that plant life in the Early Carboniferous period was more complex than expected, suggesting that Sanfordiacaulis lived at a time when plants were "experimenting" with a variety of possible forms or architectures.
"The history of life on Earth is made up of plants and animals that are unlike any living today," Gastaldo says. “Evolutionary mechanisms operating in the deep past resulted in organisms that lived successfully for long periods of time, but their forms, growth architectures, and life histories undertook different trajectories and strategies. “Rare and unusual fossils, like the New Brunswick tree, are just one example of what colonized our planet but was a failed experiment.”
