After analyzing the fossil of a tree dating back from Ancient China, researchers found it displayed a more intricate internal structure than trees today. However, how these structures grew and how the trees became tall enough to make a forest are still unclear. The vast majority of trees form a single cylinder out of xylem which grows in rings year by year just under the bark.
Berry, who has previously uncovered and studied a fossil cluster of 385-million-year-old cladoxylopsids in New York's Gilboa region, has found nothing like the recent find from China, according to a report.
But not this tree - which has an interconnected web of woody strands within the trunk instead. In fact, each xylem behaved like a tree.
As every child knows, modern tree trunks in cross-section comprise a series of concentric rings.
The study found the xylem of the earliest trees - known as cladoxlopsids - was dispersed in strands only in the outer 2 inches of the trunk - whilst the middle was completely hollow. The xylem system accommodates expansion by tearing individual strand interconnections during secondary development.
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In the largest of the two fossil trunks, above the bulge, the xylem and soft tissue occupied a ring about 50 centimeters in diameter and 5 centimeters thick, with external roots making up the remainder of the 70-centimeter-diameter tree trunk.
"By examining these extremely rare fossils, we've gained unprecedented insight into the anatomy of our earliest trees and the complex growth mechanisms that they employed", said Chris Berry, paleobotanist from the University of Cardiff research team that is studying the anatomy of the fossilized tree.
As the strands got bigger - and the volume of soft tissues between them increased - the diameter of the trunk expanded.
Within this single large tree were hundreds of "mini trees", whose trunks split apart and then repaired themselves as the tree grew.
The trees are particularly important, says Berry, because they dominated Earth during the Devonian period from 419 million to 358 million years ago. "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", said Berry, who has been studying cladoxylopsids for almost 30 years. Berry and colleagues are also interested to learn how much carbon these sort of trees were capable of sequestrating and how they affected the planet's climate. "It's insane that the oldest trees also had the most complex growth strategy", adds Christopher Berry, a plant paleontologist at Cardiff University in the United Kingdom who helped analyze the fossils. Proceedings of the National Academy of Sciences, 2017; 201708241 DOI: 10.1073/pnas.1708241114.