New Discovery of Younger Ediacaran Biota

“Kotlin Crisis” The First Extinction Event?

Researchers studying the soft-bodied Ediacaran biotas of the world generally accept that there are three distinct assemblages:

• The 575–560-million-year-old (Ma) Avalon Assemblage—best known from the Ediacaran of Newfoundland, Canada, characterized by the weird and wonderful fractal Rangeomorpha like Charnia that thrived in the deep, dark waters around the ancient continent of Avalonia.
• The 560–550-Ma White Sea Assemblage—best known from shallow marine rocks of Australia, Russia, and China, marking the acme of Ediacaran biodiversity and including some famous animal ancestors such as Dickinsonia and Kimberella.
• The 550–538-Ma Nama Assemblage—a low-diversity biota that persisted until the extinction event preceding the Cambrian Radiation event at 538 Ma.

It has long been recognized that there was a sudden drop in diversity at 550 Ma, but the percentage of taxa lost was considered less than the minimum criteria for formally considering it a mass extinction event.

However, newly published data from researchers from Memorial University in Newfoundland, Canada, have revolutionized that understanding with the description of a new “exceptionally preserved,” highly diverse Avalon-type fossil assemblage at a site known as Inner Meadow, which has been dated at 551 Ma. That is 13 million years younger than other faunas in the region.

This new information reveals that the Avalon Assemblage unexpectedly spans the entire interval encompassed by the White Sea Assemblage. Lead author Duncan McIlroy says, “The importance of the extended fossil ranges at Inner Meadow stems from the fact that the endling occurrences they document markedly increase the biodiversity loss at the 550 Ma extinction event.”

That loss of diversity in the late Ediacaran has long been recognized in Avalonia and Baltica as the “Kotlin Crisis,” making it the first extinction event that animals ever experienced. The percentage of known macroorganisms that went extinct at the Kotlin Crisis event is, in light of this newly published study, considered to be around 80%, making it a very significant event in the history of animal life.

McIlroy states that “the severity of the Kotlin Crisis extinction event is much more profound than we previously thought,” noting that “the fossil record of the earlier Ediacaran faunas is strange in that the rate of background extinction in earliest biotas is almost zero, so the Kotlin Crisis is not set against a background of progressive species loss as it is through the rest of the Phanerozoic.” He goes on to say, “It is amazing to think that the organisms fossilized at Inner Meadow immediately precede the first extinction event and that there was so much loss of diversity at a time when stasis had been the norm, and when the relatives of modern animal groups had just evolved.”

Citation: McIlroy, D., et al., 2026, Ediacaran endlings from the Avalon Assemblage and the severity of the Kotlin Crisis: First documentation of the Inner Meadow Lagerstätte, Newfoundland, Canada: Geology, https://doi.org/10.1130/G54217.1

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The Geological Society of America (GSA) is a global professional society with more than 18,000 members across over 100 countries. As a leading voice for the geosciences, GSA advances the understanding of Earth's dynamic processes and fosters collaboration among scientists, educators, and policymakers. GSA publishes Geology, the top-ranked “geology” journal, along with a diverse portfolio of scholarly journals, books, and conference proceedings—several of which rank among Amazon’s top 100 best-selling geology titles.

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