Ancient Trees “Ripped Their Skeletons Apart” To Grow

Cross-sections of 374-million-year-old tree trunks revealed a complex web of woody strands that split and repaired themselves

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A cross-section of the fossilised cladoxylopsid found in Xinjiang, China. Chris Berry, Cardiff University

If you cut into a tree, as every grade-schooler learns, you’ll find a beautiful pattern of concentric rings, each one formed during a year of the tree’s life. But this wasn’t always the case. According to Laura Geggel of Live Science, ground-breaking fossil analysis has revealed that ancient trees had a far more complex structure than the ones that exist today.

Researchers from Cardiff University, Nanjing Institute of Geology and Palaeontology, and State University of New York studied specimens from 374-million-year-old trees discovered in northwest China. The trees belong to a group known as cladoxylopsids, the fossilized remains of which have been found in a number of locations, including Scotland, Germany and upstate New York. But the fossils from China were unique because they had been preserved in a volcanic environment, which left researchers with an unprecedented amount of detail to study.

The team’s findings, published in Proceedings of the National Academy of Sciences, reveal that cladoxylopsids had an intricate anatomy unlike anything that has been seen before. Within cross-sections of the fossilized trees, researchers were surprised to discover an interconnected web of woody strands.

The strands, known as xylem, are tubes that carry water from the roots of a tree to its branches and leaves. Trees today typically form a single cylinder of xylem, “to which new growth is added in rings year by year just under the bark,” according to a Cardiff University statement. The cladoxylopsids, by contrast, had their xylem dispersed throughout the outer two inches of the tree. And the middle of the trunk was hollow.

Also remarkable was the fact that each strand of xylem had its own concentric rings—“like a large collection of mini trees,” according to the statement.

As the trees grew, soft tissue in their trunks would push the strands apart. The strands would sometimes split in a controlled manner to accommodate the expansion, reports Mary Beth Griggs of Popular Science, but examination of the fossils showed that the webs would subsequently repair themselves.

“There is no other tree that I know of in the history of the Earth that has ever done anything as complicated as this,” said Dr. Chris Berry, a palaeobotanist at the University of Cardiff, according to the statement. “The tree simultaneously ripped its skeleton apart and collapsed under its own weight while staying alive and growing upwards and outwards to become the dominant plant of its day.”

Researchers don’t quite understand the function of this unusual growth pattern. But Berry told Griggs that he plans to continue studying the fossils, looking more closely at both the roots and the xylem’s ring patterns in the hopes of learning more about why ancient trees were so much more complicated than their living cousins.

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