Scientists have discovered fossils in Argentina. Are they animals, algae or from an unknown kingdom?
Scientists have found fossils in Argentina between 545 and 560 million years old. Because of their strange anatomy, scientists cannot establish with certainty whether they were animals, algae or belonged to an unknown kingdom.
Something as majestic as the origin of animals on Earth looks subtle in the eyes of a simple mortal, to a such extent that it could even go unnoticed. A small circular crust on the face of a stone hidden 15 meters deep keeps a print of more than 500 million years. And suddenly an explosion exposes that fossil to a young geologist, María Julia Arrouy, postdoctoral fellow at the Centro de Investigaciones Geológicas (CIG) that the Consejo Nacional de Investigaciones Científicas y Técnicas de Argentina (CONICET) holds in the National University of La Plata.
Arrouy found the fossil in a routine tour by a quarry called La Cabañita, near the city of Olavarría, in the center of the province of Buenos Aires, about 350 kilometers of the national capital. Due to the mining detonations, the traces of oldest, complex, macroscopic life forms were exposed into the open: the Aspidellas, a number of assumed holdfast structures on different fronds.
The director of the group to which Arrouy belongs is Daniel Poiré, who holds a Ph.D. in natural sciences and is principal investigator of CONICET. “This is the oldest macroscopic biota found in the world, the Ediacaran,” Poiré said, referring to the geological period in which they existed, prior to the Cambrian. “It is the hinge between macroscopic and microscopic life, between 580 and 545 million years ago, in the late Ediacara. There is nothing of this size older than this. Nothing. Life as we know it today began like this. It gives chills just thinking about it.” These findings have taken place only in a few countries: Canada, Australia, Namibia, China, Russia, England, Ukraine and now Argentina.
This research, published in the journal Scientific Reports, is part of a project called “La Geología del Precámbrico del Cratón del Río de La Plata,” and includes Uruguay, Brazil and Paraguay in its study area, where Poiré believes that the next Aspidellas will be found.
Animal, plant or something else
What today is seen as a disk of no more than 6 centimeters in diameter with embossed radial rays is the imprint of a primitive life which could be an animal with the structure of an organism that was upright, with a column of water flowing inside.
Poiré says: “I still have the habit of saying fauna instead of biota because in essence I think they were animals, but today the most common is to say biota.
“When you have worked with paleobotanists, it’s hard to imagine a plant like that. Besides, plant life migrated from microorganisms to algae, that is, from the unicellular to the multicellular, and I can’t imagine a multicellular algae doing this. That’s why I lean towards the idea that they were animals.”
Poiré said water with nutrients could have circulated inside the canaliculi of the fossil’s “feathers” or fronds (those leaves arranged like the blades of a mill), “because if it is an animal it can’t produce its own food.” In that case, its main food source would have been the microplankton. According Poiré, who holds a Ph.D. in geology, the key is in the absence of photosynthesis records. “If they were plants, they would have produced their own food, but we have found nothing that makes us think of some kind of algae, some structure that could have been photosynthetic.” There aren’t any traces of microplankton either. This is because these organisms “are unfortunately preserved in dark sediments where there was no oxidation and since these sediments get reddish when they oxidize there is no record left; and if there were, they were not preserved,” he said.
The scientific community is more inclined to the animal hypothesis, but some scientists do not even rule out that the Aspidellas corresponded to a third kingdom, called Vendobionta extinguished in the Precambrian. “It could be something in between,” Poiré said. “These problems are important because they contribute to the controversy. Science never stays in one thing.”
An evolutionary hinge with a sudden and mysterious ending
The biota found in Olavarría is probably prior to the Great Explosion of the Cambrian period, the most immense burst of life on record. Before the Aspidellas, there were only microscopic organisms single-celled floating in the water and heterotrophic bacteria, amebea (protistis). “Until the Ediacaran biota appears, they were all microfossils,” Poiré said.
This finding reinforces the hypothesis that there was a sea in the area of the discovery during the Ediacaran period. The central coast of Argentina and southern Namibia were barely separated by a not very deep and mediterranean sea -20 to 40 meters deep – called Clymene.
“We imagine a sea of salty water, not very crystalline,” Poiré said. “Why not very crystalline? Because when the water is crystalline, there is usually limestone; and this is not limestone, it’s not carbonatic sedimentation, but sedimentation coming from the mainland to the sea. These biotas lie on the clay and are covered by sediment, sand, which copies the base of the animal. We believe that this sand comes through a storm stream that pulls out the frond and takes them away. We have found some of them lying down. So, the stream pulls them and it only leaves the disk. The organism dies and the sediment from above covers it, the sand covers it and only the disk remain, which is what we see. From the center of the disc, the frond comes out. The rays seen on the radius could be holdfast structures, like suction cups to grab the ground. We believe in the suction cups; I emphasize it because it’s a very important point to be study. One fossil that has this mark has been found in the United Kingdom, where you can see the rachis of the ‘feather’ or frond and the frond itself. A fossil that has this mark has been found in the UK, where you can see the rachis of the “feather” and the “feather” itself. There are entire populations of these fossils as in the Charnwood forest in the UK. Newfoundland is also famous for its populations of Ediacaran organisms and Mistaken Point was designated a World Heritage Site by UNESCO last year. “When the disk is alone, it is called Aspidella. That’s what we think,” said Poiré.
Therefore , the landscape in which the Aspidellas lived would have been more or less like Argentina, Uruguay, the south of Brazil and the south of Africa in the same continent: large rocky areas, arid climate, with no vegetation or animals in sight. That is, it was an atmosphere hostile to life, with large amounts of carbon dioxide and other harmful gases. Between Argentina and southern Africa, there was the turbulent sea of Clymene and nothing on the surface. Under the water, some microorganisms floated or clung to the bottom of the sea and the only vital thing visible to the human eye would have been that animal erected on the Aspidella.
Without predators, they should have enjoyed excellent health. However, they disappeared mysteriously just before the greatest biodiversity explosion on Earth. Some scientists consider that it was a sort of failed evolutionary experiment, a failed trial on the path to multicellular life. “They only existed during the Precambrian,” Poiré said. “Once the line of the Cambrian is crossed, with the Great Explosion, when something like mollusks and arthropods appeared, when animals appear more or less as we know them today; once that barrier is crossed, they disappeared. Perhaps some evolutionary fact made the Aspidellas the predecessors of animals similar to those we know. That is what science thinks today.” The morphology of this biota does not resemble any other living successor nor have similar fossils been found in later stages. The conclusion is, then, that the Aspidella would not have been able to adapt to the environment and they went extinct.
An obsession of two decades
Poiré has been obsessed with the Aspidella for more than 20 years. “In 1989, I went to do a postdoc in Liverpool. I went to trace fossils with a professor named Peter Crimes, one of the experts at the time. He had samples from Namibia, which was stuck to Olavarría; it was actually almost here, less than 100 kilometers away, so I thought ‘if Africans have it, why don’t we have it too?’ That’s why I organized a prospecting campaign at Cerro Negro, a mining site located in the Olavarria District, because the fossils there are the same age as the Namibian sediments containing the Ediacaran fauna.
“I’ve spent years checking dirt piles. I found little Aspidellas, like little soda bottle caps, but they were no good. Until Julia found these ones; and Julia is my apprentice, so it’s almost as if I’ve found them myself. It doesn’t matter if it’s me or my disciples, one always expects the disciples to outdo the teacher,” he said. “It is estimated that of all the life that once existed, only 10 percent is preserved as fossil; that is, overcoming the fossilization barrier is very difficult. Moreover, it has to be exposed and we have to find it. It’s not easy, and that’s what makes it thrilling.”
A mining company that supports science
The historic finding that positions Argentina in the select group of countries where such traces of remote life were found was possible because mining company Cementos Avellaneda invests in research. The Paleontological Project is developed jointly with the National University of the Center of the Province of Buenos Aires (UNICEN), the National University of La Plata (UNLP) and the Museum of Natural Sciences of that city, capital of the Province of Buenos Aires.
José María Canalicchio is the responsible for the company’s Department of Geology and Mining. Canalicchio explains that this direction was taken about 17 years ago when the company decided to combine the productive aspect with the scientific one. This allows them to obtain a double benefit: exploring new exploitation techniques and compensating society for the environmental damage generated by these type of activities. “In the old days, the companies removed from the ground what was the Quaternary, they put it in a pile and they never touched it again. We are trying to stop doing that, and, instead, we replenish the deposits so that the hole remains as small as possible,” Canalicchio said. “It is more and more about using all the materials that the deposit gives. It is a scientific and environmental commitment. The most interesting thing is that Daniel Poiré and his team of geologists have managed to confirm the stratigraphy of this area.”
The company is 100 years old and has had to adapt to new social demands because of the exponential growth of the industry. “Until 2008, this plant extracted 1,500,000 tons of stone and today extracts 4,000,000,” Canalicchio said. “The consumption is getting bigger, the holes are getting bigger, the needs are getting bigger and there comes a time when you have to make surface excavations of 60 meters deep, which were not common in the past. That means that in the future this place is going to be a huge crater.”
Those holes that mean profits for the company and damage to the environment are those that represent at the same time a great opportunity for science. “The Aspidellas are arranged horizontally and the cuts are made vertically, so it is very difficult to see the fossils unless they have been thrown into a pile. This finding was fortuitous. The sediments were taken to a stockpile because it was believed to be a type of clay that the company trades.” Canalicchio was next to Arrouy when she stumbled upon the fossil. “One day Julia was walking with me and … ‘Oh, look at this! This is what Daniel said we were going to find at some point.’ It seemed like a joke to me. Daniel argued for years that one day we would find an Aspidella. For a geologist to see that must be like touching the sky with your hands. Perhaps we would never have seen it, no matter how accustomed we are. Thanks to science we discover things.”
Poiré’s Top Five on Fossils found in South America
- Stromatolites. Olavarría (in the yellow stone quarries of Sierras Bayas). Within the Late Precambrian. Between 800 and 900 million years.
- Aspidellas, Olavarría. 560 million years. A hinge between simple and complex life forms.
- Cooksonia. Bolivia and northern Argentina. It marks the moment when plants started to leave the sea to rise to the continent, when they developed lignin, a substance that grants resistance to ultraviolet rays. Before the batrachos could do it, the plants did it. Late Silurian (between 443 and 416 million years).
- Glyptodonts, armadillos. Argentina (Olavarría, Mar del Plata, La Pampa, San Luis), Bolivia. Typical of South America.
This article was prepared by María Victoria Ennis at the Universidad Nacional Del Centro De La Provincia De Buenos Aires (UNCPBA) with assistance from Earthzine coordinator Gerardo Acosta and translator Luciano Banchio.
V. Ennis is an Argentine journalist.