We imagine the Earth of the distant past as a vegetal, exotic and luxurious paradise, but in reality we know very little about what plants and trees looked like, going back into the history of our planet. The only certain evidence available to paleontologists is preserved in fossils. And tree branches, in particular, are very rarely preserved in this way. A notable exception has just been described in the journal Current Biology: a fossil tree unearthed in Canada, which shows precisely the shape of its leaves, similar to long palm fronds, but arranged in a dense canopy, different from any living plant.
The fossil, found in the New Brunswitch area, dates back to around 350 million years ago. In the middle of the Paleozoic, therefore, just over one hundred million years before the appearance of the dinosaurs. The fossil comes from a site that in the distant past stood on the slopes of an ancient lake, and where a powerful earthquake buried Paleozoic trees and vegetation, preserving them in fossil form up to the present day. The first clues to the shape of the tree, named Sanfordiacaulis densifolia by its discoverers, were unearthed more than seven years ago. However, another four years of excavations were needed to find a total of four partial fossils of Sanfordiacaulis, which allowed us to reconstruct the shape of its foliage.
At first glance, the fronds of the ancient tree resemble those of a modern-day palm, or fern. By reconstructing the shape of its foliage and the attachment of the leaves to the trunk, however, the authors of the study soon noticed substantial differences. In fact, palms and ferns have reduced foliage, concentrated completely on the top of the plant.
“In contrast,” explains Robert Gastaldo, a researcher at Colby College in Waterville, Maine, “Sanfordiacaulis retained over 350 leaves around its trunk, and each of the partially preserved leaves we identified measured over five feet long. According to our calculations, these leaves were originally at least another meter long, which means that the plant resembled a bottlebrush with a trunk just 16 centimeters wide, surrounded by a canopy of leaves with a diameter of over five meters and half. An incredible sight to say the least.”
As we were saying, the discovery of a fossil tree with foliage is a more unique than rare event. And this means that the new study offers unique evidence of the shape that tall trees had in the distant past. According to its authors, the shape of Sanfordiacaulis densifolia was probably useful in competing to collect the maximum amount of light possible with other plants growing in the undergrowth of ancient Paleozoic forests. A hypothesis which, if confirmed, would demonstrate that ancient plant ecosystems were already extremely complex over 350 million years ago.
“The history of life on emerged lands is made up of many plants and animals that in no way resemble those that inhabit the earth today,” concludes Gastaldo. “The evolutionary mechanisms that were at work in the ancient past produced organisms that survived successfully for a very long time, but whose shapes, architectures, growth and development patterns took very different paths. Rare and unusual fossils, like this New Brunswick tree, offer us just a hint of the many organisms that have colonized our planet in the past, and ultimately proved to be unsuccessful experiments.”