Rare 3D tree fossil “unlike any alive today”

A 352-million-year-old tree fossil has been discovered in Canada which resembles nothing that we have ever seen before.

The find is also very rare because, unlike most fossilised trees, it shows what the overall tree’s form would have looked like. Usually, only the trunks of trees fossilise. This doesn’t reveal the tree’s canopy or how it might have looked overall.

Fossil tree with 1 metre scale
Fossil of Sanfordiacaulis densifolia. Credit: Matthew Stimson.

Sanfordiacaulis densifolia is described in a paper published in Current Biology.

“The way in which this tree produced hugely long leaves around its spindly trunk, and the sheer number over a short length of trunk, is startling,” says first author, palaeontologist Robert Gastaldo, a professor at Colby College in Maine, US.

Excavated in New Brunswick, Canada, the Sanfordiacaulis fossil is from the Carboniferous period (359–299 million years ago). It is an epoch named after the coal-rich deposits which are the preserved remains of Earth’s first forests.

It was a much warmer time and oxygen levels in the atmosphere were about 35% compared to 21% today. More oxygen meant insects grew to monstrous proportions – including the 3-metre-long millipede Arthropleura and dragonflies with one-metre wingspans.

Trees at the time Sanfordiacaulis was around probably tended to look like ferns or palms – though palms first evolved only about 50 million years ago.

Like ferns and palms, they had relatively few functional leaves clustered at the top of the tree.

“In contrast, Sanfordiacaulis preserves more than 250 leaves around its trunk, with each partially preserved leaf extending 1.75 metres from it,” Gastaldo says. “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.”

It is one of only a few specimens in the fossil record that show a trunk with the crown leaves still attached.

“Having the crown leaves attached to a trunk, by itself, begs the questions what kind of plant is it, how is that plant organised, and is it some form that continues to the present, or is it outside of the ‘normal’ concept of a tree? All of these questions, and more, led to this multi-year endeavour,” Gastaldo says.

Gastaldo adds that the tree might represent an evolutionary “experiment” – a form which, though successful for a time, did not persist.

“The history of life on land consists of plants and animals that are unlike any of those that live at the present,” Gastaldo says. “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 colonised our planet but was an unsuccessful experiment.”

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