Apr. 22, 1999 (Blacksburg, Va., April 22, 1999) -- Consider the architecture of modern trees -- the woody strength that builds in rings to support greater and greater height and weight, the protective bark that shields the cells that conduct water and nutrients from the earth to the farthest leaves, and the collars of extra wood that surround the bases of each branch and the way internal layers of wood dovetail at branch junctions to prevent breakage. It must have taken millions of years to evolve such a successful structure.
If it did, it happened about 360 million years ago. Archaeopteris, an extinct tree that made up most of the forests across the earth in the Late Devonian period, had the same structure as modern trees, report three scientists in the April 22, 1999 issue of Nature ("Archaeopteris is the earliest known modern tree," by Brigitte Meyer-Berthaud, Stephen E. Scheckler, and Jobst Wendt.).
After decades of operating with a model of what the tree looked like based on imprints of the leaves in fossil rocks and bits of fossilized wood, last year Meyer-Berthaud of the Laboratoire de Paléobotanique Université Montpellier in France and Scheckler, professor of biology and geological sciences at Virginia Tech in the United States, were able to examine hundreds of pieces of Archaeopteris and study the evidence that the plant was the first modern tree. It happened like this.
Almost a decade ago, Wendt, a paleontologist with the Geologisch-Paläontologisches Institut in Tübingen, Germany, was studying marine deposits in the Morocco Sahara desert, where he has been mapping marine rock formations for many years. While looking for connecting formations at a depth that would be from the Devonian period, he found logs that had been buried in ancient marine sediment that would have been hundreds of miles off the ancient coastline but were now exposed by shifting desert sands.
In 1991, Wendt reported his findings in a paper published in the Journal Facies and included photos of a 16-foot long (5m), four- to five-inch diameter tree and a cross section of that tree.
The Paleozoic team of the Institut de l'Evolution de Montpellier, also doing research concerning Moroccan fossil faunas and floras, and who had collaborated with Wendt, convinced him of the importance of this finding, reports Meyer-Berthaud. So, in 1996, Wendt collected the trunk and a number of other specimens and brought them back to Germany. Meyer-Berthaud, who has studied Archaeopteris and other ancient plants for 20 years, was allowed to borrow these fossils from the Museum of Geology and Paleontology of the University of Tübingen.
"In a preliminary analysis, I recognized at least three different species in this assemblage," Meyer-Berthaud recalls. She presented her results in 1997, in a paper co-authored with Wendt and Jean Galtier of Montpellier University in Geological Magazine, and at a conference of the Botanical Society of America held in Montreal. Scheckler was at that conference and proposed a collaboration on an international symposium on Archaeopteris.
The ancient tree and its relatives have been central to Scheckler's research for more than 30 years, since he spent summers as a graduate student searching road cuts and quarries for traces of Devonian-age plants as New York State built highways through the Catskills.
In 1998, with support from the National Science Foundation, Scheckler went on a research sabbatical to work with Meyer-Berthaud and other scientists at Université Montpellier and they went with Wendt to Morocco.
"In three days, we filled a truck," Scheckler says. Looking for tree pieces with points of branching, the researchers gathered more than 150 pieces from three locations in the Mader Basin and Tafilalt Platform. (They are presently housed in the Paleontological Collections of the Montpellier University.)
"It was the first time we had seen trunk branching on Archaeopteris, and we found hundreds of examples," he reports. "And we found big roots, which had previously been mostly conjecture."
From cell details of slices of trunks, Meyer-Berthaud was able to show that these ancient trees also had lateral buds on their trunks and branches. "This was unique to Archaeopteris," says Scheckler. "It was the only plant at that time that could bud and continue growing after the main axis tip died; although seed plants now have that ability."
"The attachment of branches was the same as modern trees, with swelling at the branch base to form a strengthening collar and with internal layers of wood dovetailed to resist breaking," says Scheckler. "We had always thought this was modern but it turns out that the first woody trees on earth had this exact same design."
Another unique feature of Archaeopteris while it dominated ancient forests was its long-life. Archaeopteris was the first long-lived perennial. "Other plants ran out of ability to grow," says Scheckler. These trees could grow for 10-50 (100) years or more. They had no apparent life span."
Some of the trees that Meyer-Berthaud and Scheckler found were possibly 40- to 50-years-old when they fell into the sea some 350 million years ago. There are differences between Archaeopteris and modern trees, Scheckler points out. Archaeopteris reproduced by releasing spores rather than by producing seeds. That is one of the reasons why paleobotanists suspect that today's trees come from a sister line of plants, the "progymnosperms." Archaeopteris is more like an ancient aunt than a direct ancestor, but became extinct within a short period of time at the end of the Devonian age.
Before they left, though, Archaeopteris trees changed the world, Scheckler reports.
The earth's atmosphere was changing rapidly, going from perhaps 10 percent to 1 percent CO2 and from about 5 percent to 20 percent oxygen over a 50-million year period in the (late) Devonian period. All plants were responsible for the transformation, but Archaeopteris was important because it made up 90 percent of the forests during the last 15 million years when these changes accelerated, says Scheckler.
"Its litter fed the streams and was a major factor in the evolution of freshwater fishes, whose numbers and varieties exploded in that time, and influenced the evolution of other marine ecosystems. It was the first plant to produce an extensive root system, so had a profound impact on soil chemistry. And once these ecosystem changes happened, they were changed for all time. It was a one-time thing.
"Archaeopteris made the world almost a modern world in terms of ecosystems that surround us now," Scheckler concludes.
Meyer-Berthaud and Scheckler are organizing a symposium on Archaeopteris for the International Botanical Congress, which will meet in St. Louis in August 1999. "The symposium will address how Archaeopteris might have grown, lived, and reproduced, as well as how it might be related to its nieces, nephews, and cousins, the seed plants. Based on what we have been able to learn, researchers will present new models that can be tested," Scheckler says.
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