May 20, 2022

Before the first mammals, before dinosaurs roamed the earth, a plant grew in Gondwana, a vast continent in the southern hemisphere.

Almost 280 million years later, in what is now Brazil, scientists have identified the fossil remains of this plant as an early member of a lineage called cycads or cycadales, which continues to this day. The discovery expands scientific understanding of the hardiness of these plants, which persisted through two mass extinctions.

“The vegetative anatomy of this plant is remarkably similar to that of today,” said Rafael Spiekermann, PhD student at the Senckenberg Research Institute and Museum of Natural History in Germany and lead author of a paper describing the fossil in the Review of Paleobotany and Palynology.

The species obtained was called Iratinia australis; “Australis” is Latin for “south” and the fossil comes from the southern part of a rock layer known as the Irati Formation. It’s a small piece of wood – a little over five inches long, about 2.5 inches in diameter – but that was enough to see that it shares key characteristics with the plants living today.

“If you cut a cycad with a machete today,” said Mr. Spiekermann, “you will see the same anatomical pattern that you can see in our fossil.”

The surviving Cycadales are often referred to as “living fossils,” much like today’s coelacanth fish, which share many of the same characteristics as the ancestral fish from hundreds of millions of years ago.

This lineage experienced two cataclysms when most of the life of the planet was killed. The first occurred at the end of the Permian geological period 250 million years ago and is often referred to as the Great Die. It was the largest mass extinction in Earth history and opened the evolutionary door to the rise of the dinosaurs. The other was extinction 66 million years ago, which ended the age of the dinosaurs.

“It’s a really long story on Earth,” said André Jasper, professor of biology at the University of Taquari Valley in Brazil and author of the paper. “You can find it, this type of plant, in Australia, in Asia, in Africa, in America. It has spread all over the world. “

Cycadales never dominated the plant kingdom, although they thrived in certain places. Their heyday was more than 120 million years ago before they, and even older plants like conifers, were overtaken by the advent of flowering plants that reproduced faster and adapted to changing ecological niches.

“Those guys were dinosaur food,” said Dennis Stevenson, retired senior curator at the New York Botanical Garden and an expert on cycadales who was not involved in the research.

Cycadales never disappeared, however, and there are around 350 species today. Perhaps best known is the sago palm, an ornamental plant that looks like a small palm but is actually not a palm.

Rather, like all Cycadales, a sago palm has a characteristic structure of veins that run from its leaves through its trunk. The fossil Cycadales also retain this feature, known as belt leaf traces.

The Iratinia australis fossil was unearthed a few decades ago. Because of its leaf shapes, botanists mistakenly identified it as belonging to a different group of plants known as lycopsids. At that time there were numerous Lycopsids in this part of Gondwana, so the fossil did not receive much attention until Mr. Spiekermann, who is working on his PhD on Lycopsids, took a closer look.

“I saw a completely different anatomy,” said Mr. Spiekermann.

Some fossilized leaves of the same period, believed to be parts of cycadale plants, were previously found in China. But this was the first look at the woody part of such an ancient cycad.

“The anatomical details are just amazing,” said Dr. Stevenson. “I think it’s what every paleobotanist dreams of – and the first to be identified in the rocks of the former Gondwana.”

The widespread geographical distribution suggests that Cycadales had been around for a while back then.

“The idea is, wow, we have one of those things here in Brazil and the other in China,” said Dr. Stevenson. “These people have to be much older than what we have in the fossil record to be anywhere on earth.”

William A. DiMichele, curator of paleobotany at the Smithsonian National Museum of Natural History who was not involved in the research on Iratinia australis, said the discovery was part of a trend that ancient plants were turning out to be even older.

“There have been many discoveries in the last 10 to 15 years where plants appeared much earlier than previously thought,” he said.