Around 570 million years ago, life on Earth was exclusively confined to the oceans. Large invertebrates with peculiar shapes inhabited the seafloor; these organisms anchored themselves to the bottom, absorbing nutrients from the water via fleshy appendages. These life forms, collectively known as the Ediacaran biota, eventually vanished, but scientists long debated the severity of their extinction event.
A new study published in the journal Geology suggests a reassessment of the scope of the so-called Ediacaran crisis—the event that wiped out many of these creatures. According to the researchers, this crisis may have been far more devastating than previously thought, rivaling the dinosaur extinction 66 million years ago in terms of the proportion of species lost.
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Shuhai Xiao, a paleobiologist at Virginia Tech who was not involved in the study, points out that while the Ediacaran crisis claimed fewer overall organisms than the Great Dying event approximately 252 million years ago, “this extinction, in terms of the percentage of animals that died out, is comparable to its later, more famous counterparts.”
The research focuses on fossils within a collection known as the Avalon assemblage—the earliest large and complex organisms recorded in the paleontological record. These were first discovered in 1958 on the Avalon Peninsula in Newfoundland. These soft-bodied entities thrived in deep-water environments between 574 and 560 million years ago. Paleontologist Lidia Tapan, not involved in the study, explains that this group included organisms resembling lichens, massive bacterial mats, and “an entirely extinct kingdom of life that no longer exists on Earth,” with debates about their exact animal classifications continuing to this day.
Fossil evidence indicates that around 560 million years ago, the Avalon assemblage experienced a relatively minor extinction, after which it was succeeded by a more varied group: the White Sea assemblage. About 10 million years later, this successor community faced a much larger extinction event—the Ediacaran crisis.
The study’s lead author, paleontologist Duncan McIlroy from Memorial University of Newfoundland, describes the Ediacaran crisis as “the first significant mass extinction event that animals ever experienced.” He notes that prior estimates suggested the demise of about 65% of all species.
Through new excavations at a site in Newfoundland dubbed the “Lawn Quarry,” McIlroy and his team uncovered exceptionally preserved remains of at least 19 genera of Ediacaran creatures, including numerous branched filter-feeders typical of other known Avalon outcrops. “The moment we cleared away the moss and soil on the first day, it was clear this was a very special location,” McIlroy recalls. “The fossils were exquisitely preserved, and many showed little sign of weathering.”
By employing uranium dating on tiny zircon fragments found in ancient ash layers, the researchers determined that these new fossils are approximately 551 million years old—significantly younger than most previous estimates. This implies that the Avalon assemblage organisms persisted for an additional 10 million years than previously believed, perishing precisely during the Ediacaran crisis rather than earlier.
With this new data, the crisis’s severity appears much greater: instead of 65% of species, the extinction rate might approach 80%, qualifying it as a mass extinction event. “Sometimes in science, an idea or new data has such broad implications that it’s mind-boggling; I’m not sure I slept much that first night,” McIlroy admits.
The causes behind the demise of these creatures remain unclear. Hypotheses include a sharp drop in ocean oxygen levels or increased predation pressure from early cnidarians, distant ancestors of modern jellyfish. McIlroy anticipates that further excavation at the Lawn Quarry and other Newfoundland sites will help uncover answers and identify new species that fell victim to the crisis, according to Planet Today.
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