Sanfordiacaulis densifolia is an extinct tree species that existed between 359 and 347 million years ago (Carboniferous period) in what is now New Brunswick, Canada. Its architecture consisted of an unbranched, 16-cm-diameter trunk with compound leaves arranged in spirals of 13 cm and compressed into 14 cm of vertical trunk length. Compound leaves in the upper 0.75 m of the trunk measured over 1.75 m in length and preserved alternately arranged secondary laterals beginning at 0.5 m from the trunk; the area below the trunk had only persistent leaf bases. Sanfordiacaulis densifolia shows that Early Carboniferous vegetation was more complex than realized, signaling that it was a time of experimental, possibly transitional and varied, growth architectures.
Sanfordiacaulis densifolia. Image credit: Tim Stonesifer.
Trees first appear in the mid-Devonian period (393 to 383 million years ago), although modern woody trees don’t appear until about 10 million years later.
Evidence of arborescence (tree-like structure) is based primarily on mudcast, sandcast, or permineralized stumps or extensive rooting structures in fossilized soils.
Under unique preservational circumstances, these early trees were fossilized with rooting-and-crown structures attached to their trunks.
“The way in which Sanfordiacaulis densifolia produced hugely long leaves around its spindly trunk, and the sheer number over a short length of trunk, is startling,” said Dr. Robert Gastaldo, a paleontologist at Colby College.
“The forms taken by these 350-million-year-old trees look something like a fern or palm, even though palms didn’t arise until 300 million years later.”
“However, the functional leaves in ferns or palm trees cluster at the top and are relatively few.”
“In contrast, Sanfordiacaulis densifolia preserves more than 250 leaves around its trunk, with each partially preserved leaf extending 1.75 m from it.”
“We estimate that each leaf grew at least another meter before terminating.”
“This means that the ‘bottle brush’ had a dense canopy of leaves that extended at least 5.5 m around a trunk that was non-woody and only 16 cm in diameter. Startling to say the least.”
Sanfordiacaulis densifolia with spirally arranged compound leaves. Image credit: Gastaldo et al., doi: 10.1016/j.cub.2024.01.011.
Dr. Gastaldo and colleagues examined five fossilized specimens of Sanfordiacaulis densifolia.
The fossils came from Sanford Quarry, which is part of the Albert Formation in New Brunswick, Canada.
“These fossils were preserved by earthquake-induced, catastrophic burial of trees and other vegetation along the margin of a rift lake,” Dr. Gastaldo said.
“The first fossil tree was unearthed about 7 years ago from the quarry, but it only included one partial sample.”
“It took several years for another four specimens of the same plant, in close spatial proximity, to also be found.”
“One of the specimens revealed how the leaves departed from the top of the tree, which makes it absolutely unique.”
“It’s one of only a few in a fossil record spanning more than 400 million years in which a trunk is preserved around which the crown leaves are still attached.”
Actual and reconstructed tree heights and biostratigraphic ranges of Middle Devonian to Pennsylvanian trees. Image credit: Gastaldo et al., doi: 10.1016/j.cub.2024.01.011.
Sanfordiacaulis densifolia likely relied on its unusual growth form to maximize the amount of light it could capture and reduce its competition with other plants on the ground.
The findings offer important insights into the evolution of plants and arborescence, meaning plants that grow to a tree height, or at least 4.5 m at maturity.
They’re also a reminder that over the history of life on Earth, there have existed trees that look unlike any we’ve ever seen before.
“We all have a mental concept of what a tree looks like, depending on where we live on the planet, and we have a vision of what is familiar,” Dr. Gastaldo said.
“The fossil on which we report is unique and a strange growth form in the history of life.”
“It is one of evolution’s experiments during a time when forest plants underwent biodiversification, and it is a form that seems to be short lived.”
“The history of life on land consists of plants and animals that are unlike any of those that live at the present,” he added.
“Evolutionary mechanisms operating in the deep past resulted in organisms that successfully lived over long periods of time, but their shapes, forms, growth architectures, and life histories undertook different trajectories and strategies.”
“Rare and unusual fossils, such as the New Brunswick tree, is but one example of what colonized our planet but was an unsuccessful experiment.”
A paper on the findings was published in the journal Current Biology.
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Robert A. Gastaldo et al. Enigmatic fossil plants with three-dimensional, arborescent-growth architecture from the earliest Carboniferous of New Brunswick, Canada. Current Biology, published online February 2, 2024; doi: 10.1016/j.cub.2024.01.011
