Fossils from a forest with 165 trees were found inside rocks in the city of Ortigueira, Paraná. The discovery depicts life forms 290 million years old. With roots still fixed in the substrate of the time, the trees preserve their vertical position, which is rare.
There are only records of this in Patagonia and Rio Grande do Sul.
The finding should contribute to studies on biological, geological and ecosystem evolution and past climates.
The research is by Thammy Ellin Mottin, a doctoral student in geology at UFPR (Federal University of Paraná), and had the collaboration of researchers from the University of California, Daves (USA). The article was published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.
“The Ortigueira lycophyte forest is the most important among all other rare occurrences in the entire southern hemisphere of the Earth”, says Mottin.
She says that at the time this forest existed, about 290 million years ago, the southern hemisphere was united in a single continent called Gondwana — formed by South America, Australia, Africa, Antarctica and India.
The discovery, says the researcher, is the most important in terms of quality of preservation and numbers of trees preserved.
“In two other places where lycophytes are preserved in a position of life (Patagônia Argentina and Rio Grande do Sul), the trunks are deformed and in much lower numbers”, she adds, noting that the plants were one of the first to colonize the terrestrial environment.
In total, 165 trees were found. Of these, 115 are exposed in cuts of a new road and train track, recently opened in the region. Another 50 were detected in the subsurface. “Surely there must be hundreds more of them still.”
The finding of the fossils took place during fieldwork in 2018, together with researchers at the University of California. “The discovery was a real surprise, as we were only there to take some samples for chemical analysis and study the rocks in the region”, says the Brazilian researcher.
Mottin believes they were the first geologists to analyze the terrain, as the road was recently opened at the site. According to her, the work should have had a better geological analysis before starting.
“I think she did a lot of damage, because they discarded a lot of material without knowing what it was about. But at the same time, if they hadn’t built it, maybe no one would have found it.”
Between field and laboratory analyses, the team worked on the fossilized forest for a year. “But the article took a while to be published because, in the meantime, there was an exchange for the University of California and the pandemic.”
The doctorate, which she defends in early July, focuses on the study of glaciation at the end of the Paleozoic Era, and the shift to a post-glacial period, which took place around 300 million years ago.
“These ancient climate events are used as analogues for the current climate of the Earth, which is in a glacial phase, and whose transition to the post-glacial period has not yet occurred, will occur millions of years from now”, explains Mottin. “But no one can predict how and when, so we studied the ancient records.”
According to her, the existence of these trees is the record of a unique climate change event in the past, “considered the transition from an ‘icehouse’ (glacial period) to a ‘greenhouse’ (post-glacial or greenhouse effect) state between the Carboniferous and the Permian”.
The rarity of this forest lies in the fact that it was fossilized while standing. “The natural process of death of trees ends up with them rotting and falling to the ground, in the substrate they colonized. Or parts of this tree are carried away by rivers, sea water, going away from their habitat.”
In the case of the Ortigueira lycophyte forest, the trees were buried by sediment while they were still alive. “The process was so rapid and catastrophic that they remained in the exact place where they lived and were progressively covered by sediment from a giant river flood.”
The trees did not fall, as the sediment invaded the place where they lived, on the banks of a river, in a coastal area. “The best comparison is to imagine a forest and hundreds of trucks of sand being dumped around them. They won’t be knocked down, as the sand is ‘protecting’ and at the same time killing them.”
Mottin and other researchers from the Department of Geology at UFPR, the Laboratory of Basin Analysis (LABAP) and the University of California managed to map about 50 trees in the subsurface. They used a technique called ground penetration radar (GPR), which gives clues to what’s beneath the ground.
The next necessary step, says Mottin, is the creation of a conservation project. “It has to be done by competent bodies, such as the Geological Service of Brazil (CPRM), which works with the conservation of geological heritage, through the creation of geological and paleontological sites”, he concludes.
