3D fossils of bizarre ancient trees discovered

Artist’s impression of the approximately 350 million year old Sanfordia tree with human silhouettes as a scale. © Tim Stonesifer

They looked like green bottle brushes: Around 350 million years ago, tree-like plants that we no longer recognize today grew in the forests of the world. This is shown by amazingly three-dimensionally preserved fossils from Canada, which were apparently preserved by a sudden burial during an earthquake. The strange tree structures show how nature “experimented” with different plant models in the early Carboniferous period, say the scientists.

Life forms became increasingly more complex - but major breakthroughs also shaped the early history of the development of life on our planet. One of these groundbreaking innovations was the so-called arborescence - the development of plants into tree-like plants: according to fossil discoveries, in the Devonian era, plants first developed trunks and crowns in order to rise several meters high from the ground. This concept proved to be enormously successful: especially in the following Carboniferous Age, the trees formed huge forests from which the oldest coal deposits on earth emerged.

Insight into mysterious forests

Fossil records have already provided some clues about the characteristics of early Carboniferous trees. However, these are usually fragments of fossil roots, tree stumps or trunks. They show that some species reached heights of over 20 meters around 350 million years ago. But in most cases no traces of leaves and other crown structures have been preserved to give an impression of the overall shape of these plants. But now the research team led by Robert Gastaldo from the Smithsonian National Museum of Natural History in Washington is reporting amazing finds that provide a detailed impression of a tree from the early Carboniferous Age.

The fossils were discovered in a quarry in the eastern Canadian Atlantic province of New Brunswick and were dated to be around 350 million years old. During recovery, an astonishing condition emerged: the plant remains are not very fragmented and are not preserved in a crushed, one-dimensional form, as is usually the case. Instead, the crown structures are still attached to the trunk and preserved in a three-dimensional arrangement. As the researchers explain, it is obvious that this preservation is due to a sudden process: the plant structures were probably filled with sediment during an earthquake, stabilized and then petrified. Using these relics recovered in blocks, the research team was now able to pursue the exciting question of what characteristics the tree-like plants possessed.

A tree like a bottle brush

As it turned out, the plant called Sanfordia densifolia was extremely bizarre and can no longer be assigned to any plant form today. According to estimates, the tree was around three meters high and had a trunk diameter of around 16 centimeters. Elongated leaf structures with lateral branches grew out of the trunk in a spiral upwards direction. Gastaldo compares the structure of Sanfordia to that of a bottle brush. “There are more than 250 such leaves, 1.75 meters long, preserved around the trunk. We estimate that each leaf grew at least another meter before it ended,” says Gastaldo. This resulted in the image of a dense crown at least 5.50 meters wide.

“The way this tree produced enormously long leaves around its spindly trunk, and the sheer number on a short piece of trunk, is astounding,” Gastaldo says. As he and his colleagues explain, Sanfordia's characteristics likely resulted from the plant trying to capture dim light as effectively as possible. Given that significantly taller trees from that era are documented, growth under the higher forest canopy can be assumed. According to the authors, this is an indication that the plant community in the forests of the early Carboniferous period was structured more complexly than previously thought.

But although Sanfordia was apparently well adapted to the twilight conditions of the middle layer of ancient forests, this model of evolution apparently did not have lasting success: “The fossil we report here is unique and a strange growth form in the history of life. It was a development at a time when forest plants were developing. “Sanfordia is an example of what evolution once produced but remained an unsuccessful experiment,” says Gastaldo.

Source: Cell Press, specialist article: Current Biology, doi: 10.1016/j.cub.2024.01.011

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