Trees are believed to have originated hundreds of millions of years ago. Ever since, evidence of these ancient plant sentinels has been in short supply.
Now, a new discovery of uniquely 3D tree fossils has opened a window into what the world was like when the planet’s early forests were beginning to evolve, expanding our understanding of the architecture of trees throughout Earth’s history.
Five tree fossils buried alive by an earthquake 350 million years ago were found in a quarry in the Canadian province of New Brunswick, according to a study published Friday in the journal Current Biology. The authors said these new and unusual fossil trees not only bear a surprising shape reminiscent of a Dr. Seuss illustration, they reveal clues about a period of life on Earth of which we know little.
“They are time capsules,” said Robert Gastaldo, a paleontologist and sedimentologist who led the study, “literally little windows into deep-time landscapes and ecosystems.”
Coauthors Olivia King and Matthew Stimson unearthed the first of the ancient trees in 2017 while doing fieldwork in a rock quarry in New Brunswick. One of the specimens they discovered is among a handful of cases in the entire plant fossil record — spanning more than 400 million years — in which a tree’s branches and crown leaves are still attached to its trunk.
Few tree fossils that date back to Earth’s earliest forests have ever been found, according to Gastaldo. Their discovery helps fill in some missing pieces of an incomplete fossil record.
“There are only five or six trees that we can document, at least in the Paleozoic, that were preserved with its crown intact,” said Gastaldo, a professor of geology at Colby College in Waterville, Maine.
Most ancient tree specimens are relatively small, he noted, and often discovered in the form of a fossilized trunk with a stump or root system attached. For his colleagues to find a preserved tree that could have been 15 feet tall in its maturity with an 18-foot diameter crown left the paleontologist “gobsmacked.”
Ancient earthquake burial
The researchers excavated the first fossil tree about seven years ago, but it took another few years before four more specimens of the same plant were found in close proximity to one another. Dubbed “Sanfordiacaulis,” the newly identified species was named in honor of Laurie Sanford, the owner of the quarry where the trees were unearthed.
The forms taken by these previously unknown 350 million-year-old plants look somewhat like a modern-day fern or palm, per the study, despite the fact that those tree species didn’t appear until 300 million years later. But while the tops of ferns or palms as we know them boast few leaves, the most complete specimen of the newly discovered fossils has more than 250 leaves preserved around its trunk, with each partially preserved leaf extending around 5.7 feet (1.7 meters).
That fossil is encased in a sandstone boulder and roughly the size of a small car, according to Stimson, an assistant curator of geology and paleontology at the New Brunswick Museum.
The unique fossilization of the cluster of trees is likely due to a “catastrophic” earthquake-induced landslide that took place in an ancient rift lake, he said.
“These trees were alive when the earthquake happened. They were buried very quickly, very rapidly after that, at the bottom of the lake, and then the lake (went) back to normal,” Stimson said.
Finding complete fossil trees is rare and much less common than finding a complete dinosaur, according to Peter Wilf, a professor of geosciences and paleobotanist at Pennsylvania State University who was not involved with the study. Wilf noted via email that the “unusual” new fossil tree was a relic of a time period from which there are almost no tree fossils.
“The new fossils are a milestone in our understanding of how early forest structure evolved, eventually leading to the complex rainforest architectures that support most of Earth’s living biodiversity,” Wilf added.
‘Very Dr. Seuss’
To King, a research associate at the New Brunswick Museum who found the group of fossils, the Sanfordiacaulis would have looked like something plucked straight out of Dr. Seuss’ most popular works.
“You know in ‘The Lorax,’ the trees have these big pom-poms at the top and narrow trunks? These probably have a similar structure. You have this massive crown at the top, and then it does narrow and paper into this very small trunk,” King said. “It’s a very Dr. Seuss-looking tree. It’s a weird and wonderful idea of what this thing could look like.”
Much of evolution is experimental, with success often measured by a species’ versatility, or ability to adapt to many different places and conditions. The peculiar set of tree fossils presents proof of a “failed experiment of science and evolution,” Stimson added. “We’re really starting to paint that picture as to what life was like 350 million years ago.”
Looking forward
Fossils such as the Sanfordiacaulis are not just useful in helping humans understand how life changed in the past, they can help scientists figure out where life on our planet might be headed next.
The existence of this particular species suggests that trees of the period were starting to occupy different ecological niches beyond what was previously understood, according to the researchers behind its discovery.
Gastaldo sees this as an indication that plants — much like early invertebrates — were experimenting with how they adapted to the environment. The earthquake that likely led to the trees’ fossilization also offers new geological evidence of what may have been occurring in Earth’s systems at the same moment in time.
“This is really the first evidence we have of (a tree) that would be between what grows on the ground and what would tower way above the ground,” Gastaldo said. “What else was there?”