The 385 million-year-old fossilized root web has led scientists to re-imagine what the world's first forests might have looked like.
The picture they painted could not be more different from what is now in its place. Not far from the small town of Cairo in upstate New York, under an old road department quarry, scientists have restored the remains of a mighty and mature ancient forest, which was home to at least three of the world's first tree-like plants.
Some of these early "wannabe" trees (known as cladoxylopsids) looked like large celery stalks that rose 10 meters (32 feet) into the sky. Others resembled pine trees, but with hairy, fern-like leaves (Archaeopteris). The third long-extinct plant was palm-like, with a bulbous base and a canopy of fern-like branches (Eospermatopteris).
Seven parallel cross-sections of the Cairo site suggest that these primeval trees were quite old and large. Therefore, they were not located tightly to each other, but were relatively scattered over the floodplain, which varied depending on the season.
Dry periods were a regular part of the cycle, and yet the Cairo Forest, along which the Catskill River flowed, grew primitive trees that we previously thought could only survive in swamps or river deltas. These tree-like plants belong to the genus Eospermatopteris and look like tall ferns standing on bulbous stumps.
Since these tall plants have shallow roots that do not branch out, they probably did not tolerate drier conditions - which is why their presence in the ancient floodplains of Cairo is puzzling.
Scientists have previously found evidence of Eospermatopteris trees only in humid lowlands, such as the prehistoric Gilboa site, also in New York State.
However, unlike the homogeneous swamps of Gilboa, the Cairo site is 2–3 million years older and its landscape is highly varied. Researchers believe that it once consisted of an abandoned canal with banks and a local depression that was filled with water only in certain seasons.
However, Eospermatopteris trees have flourished here for perhaps over 16,000 years. Their roots have adapted to semi-arid conditions and the possibility of short-term flooding, the researchers say.
Other trees in the area were found to be more prepared for periods of water scarcity.
At the Cairo site, the researchers also found evidence of deeper root systems in extinct pine-like plants belonging to the genus Archaeopteris. These plants are more developed than trees of the genus Eospermatopteris, have more woody branches and true leaves, capable of photosynthesis; they also have deeper roots that sometimes extend 11 meters wide (36 feet) and 7 meters deep (23 feet).
It was these traits that were thought to have allowed primitive fern-like trees hundreds of millions of years ago to break out of low-lying marshes and into drier areas such as river floodplains, where water levels can rise and fall.
But new results show that even primitive Eospermatopteris trees, lacking true leaves and deep roots, may have left the swamp in search of drier conditions.
"This finding suggests that the earliest trees could colonize a variety of environments and were not limited to humid environments," explains evolutionary ecologist Hudadad of Binghamton University, New York.
"The trees could withstand not only drier conditions, but also the harsh expansive clay conditions that prevailed in the Catskill Plains."
Why so often do we see that Eospermatopteris trees dominated prehistoric deltas, and Archaeopteris trees dominated river floodplains? Since these trees still use spores rather than seeds for propagation, then, of course, they should have been more likely to settle near rivers or water sources that can carry their genes over long distances.
The authors of the new study believe that fossils can deceive us. The prehistoric Cairo forest is believed to have disappeared as a result of prolonged flooding that flooded the trees and killed them. But the sedimentary rocks that were deposited after this could preserve their roots, which happens extremely rarely in river floodplains and most often in deltas.
"It is possible that due to the ideal conditions necessary for the conservation of landscapes and organisms, the fossils were assigned to low-lying areas, leading to the conclusion that Eospermatopteris were limited in their morphology to deltaic environments," the authors write.
Given the immense age of Cairo's prehistoric forest, the authors doubt that its structure is an anomaly. On the contrary, they argue that he "is most likely a representative of mature forests of that time, which have not been preserved or have not yet been discovered."
The study was published in the journal PLOS One.