Nine million years before the greatest extinction in the history of the Earth, three-quarters of the species in what is now South Africa's Karoo region vanished. Combined with evidence for the loss of oceanic species at the same time, the finding strongly supports the theory that the late Permian was marked by two, rather than one, of the planet's worst disasters.
The world has experienced at least five mass extinctions, and is now in the throes of another. The most famous are the Cretaceous-Paleogene event in which the dinosaurs disappeared and the “Great Dying” at the end of the Permian era when 96% of marine species and 70% of terrestrial vertebrates vanished from the fossil record. Understanding these events is crucial in getting to grips with the Earth's evolutionary past, and may also provide lessons on how to minimize the damage today.
In the Proceedings of the Royal Society B, a team led by Dr. Michael Day of the University of the Witwatersrand, Johannesburg, has provided powerful evidence for a sixth apocalypse, the mid-Permian mass extinction, which preceded the Great Dying by nine million years.
The existence of a mass extinction around this time has been greatly debated. Many marine species disappeared 260 million years ago, but evidence from the land was far more ambiguous. "A mid-Permian extinction event on land has been known for some time but was suspected to have occurred earlier than those in the marine realm,” said Day.
However, the lower Beaufort Group of South Africa's Karoo Basin hosts "the richest record of middle Permian land-living vertebrate animals," Day says. Analysis of these fossils “reveals a 74-80% loss of generic richness” between two zones, the paper reports. Uranium-lead zircon dating of the transition places it at around 260 million years ago (plus or minus 81,000 years), matching neatly with estimates for the marine extinction. “The new date suggests that one event may have affected marine and terrestrial environments at the same time, which could mean its impact was greater than we thought," Day added.
The scale of the mid-Permian extinction was dwarfed by the one that would follow it, but in terms of loss of diversity, it may have matched or exceeded any of the four other mass extinctions. Explanations are likely to be debated for a long time. We are still unsure what caused the Great Dying, although volcanic eruptions and microbes that released vast quantities of methane are the leading contenders.
Species that vanished from the fossil record in the mid-Permian include dinocephalians, the largest land animals of the day. Nine million years was not long enough to replace these mighty beasts, some of which grew to a weight of two tonnes and a length of 4.5 meters (15 feet). The late Permian, between the two disasters, lacked similarly large terrestrial creatures.
A previous study on the same formation, along with rocks from Portal Mountain, Antarctica, suggested a similar coincidence of terrestrial and marine extinctions, but the timing wasn't precise enough to etch the event into textbooks.