Our planet’s worst mass extinction occurred 252 million years ago when massive volcanic eruptions triggered catastrophic climate change.
The vast majority of animal species became extinct, and when the dust settled, the planet entered the early days of the dinosaur age.
Scientists are still learning about the patterns in which animals went extinct and which ones survived, and why. In a new study in PNAS, researchers found that while extinctions were rapid in the oceans, life on land underwent a longer, more protracted period of extinction.
“People assumed that because the sea extinction occurred in a short period of time, life on land should have followed the same pattern, but we found that the sea extinction may be a punctuation for a longer, more drawn-out event.
on land, ”said Pia Viglietti, a postdoctoral researcher at Chicago’s Field Museum and the lead author of the PNAS study.In fact, the focus for studying the Earth’s extinction was, ‘Can we match the pattern in the Earth realm with what is being observed in the oceans?’
And the answer is, “Not really,” says Ken Angielczyk, senior author and curator of the Field Museum’s paper on vertebrate paleontology. “This article is the first to really focus on vertebrates, saying, ‘No, something was going on that was unique to the Earth realm.’ ”
Part of the reason scientists had looked to the sea’s extinction for clues as to what was happening on land is that there is a more complete fossil record of underwater life.
If you want to become a fossil dying from water, where your body quickly gets under sediment, that’s a good way to do that.
As a result, paleontologists have known for some time that a massive extinction occurred at the end of the Permian period 252 million years ago and that within 100,000 years, more than 85% of ocean-dwelling species became extinct.
And while that seems like a long time to us, it is very fast in geological time. The marine version of the end of Permian extinction took 100,000 years out of the full 3,800,000,000 years of life – the equivalent of 14 minutes a full year.
To find out what happened to life on land, Viglietti, Angielczyk and their colleagues examined fossils from 588 four-legged fossil animals living in the present-day Karoo Basin in South Africa at the time of the Permian mass extinction .
“The region where we found the fossils for this study is absolutely beautiful. The verdant mountainous slopes are so inviting on a crisp summer morning that it makes the heat to come bearable, ” said Zaituna Skosan, the palaeontology collection manager of the Iziko South African Museum and one of the paper’s co-authors.
“Finding good fossils is the best feeling, but it is also short-lived because you have to concentrate and keep looking for your next find. Even the best fossil finder sometimes overlooks a great find. “
The researchers created a database and separated the fossils by age, grouping the specimens at time intervals of 300,000 years.
This approach allowed the researchers to quantify the appearance and disappearance of different species and look at the bigger picture of life over time, rather than relying solely on individual specimens to tell the whole story.
“Our approach takes the data together and says, okay, within this timeframe we have these types, but as we get higher we have these other types.
By applying sampling methods to these bins, we can help correct problems such as collecting more or fewer samples at different time intervals or places. Ultimately, it allows us to quantify how much extinction is taking place and how quickly new species appear, ”says Viglietti.
“Instead of paying too much attention to a fossil, you collect hundreds of observations in roughly the same time interval.” “To find out extinction patterns based on hundreds of fossils, we used a kind of math called statistics.
When a species disappears, it could either be extinct, or it could still be there, waiting to be discovered, but so far unnoticed, ” said Roger Benson, a professor of paleobiology at the University of Oxford and one of the co – authors.
“We had to deal with that before we could have any confidence about the timing of extinctions. The math is already known, so the statistical work involved writing computer algorithms to extract that all-important signal of extinction from the data.
“One of the species that helped reveal patterns of extinction and recovery was Lystrosaurus, a herbivorous early mammal relative that ranged from the size of a small dog to a cow, depending on the species.
” It had a beak and tusks, it wasn’t the most attractive animal, but I have a soft spot for Lystrosaurus because it was just the first animal I studied as a student, so when I came full circle with Lystrosaurus in this study, I’m quite happy, ”says Viglietti.
Lystrosaurus is what paleontologists call a ‘disaster taxon’ – a group that thrived at a time when most other lives were struggling.
“Lystrosaurus is like a poster child for the end of the Permian extinction that has always been portrayed as this animal thriving in the aftermath of all this extinction and just taking it over,” says Viglietti.
“But we see Lystrosaurus appear before the extinction even started, it was already in abundance. It got us thinking about what drove that abundance – whether the Lystrosaurus took over the arid landscape only after other animals became extinct, or whether the environment was changing and Lystrosaurus was adapting to these changes that killed all these other species.
Our best guess is the last. By examining fossils like Lystrosaurus, the researchers showed that the Permian extinction looked very different on land than it did in the oceans – it was a much longer, drawn-out affair.
land ten times as long, about two hours and twenty minutes. It is not clear exactly why the mass extinction on land took place so much more slowly. ”The changes in the Earth’s climate were cumulative and increased over time.
added up.Ecosystems were slowly disrupted, and then it just got to a point where everything collapsed, like the straw breaking the camel’s back, ” says Viglietti. “Everything’s all right until it’s no more.”
One reason for the discrepancy could be that the oceans can absorb chemical changes and stabilize themselves to some degree.
“In the current climate crisis, the oceans can absorb a lot of carbon dioxide or the temperature can rise without people realizing it, and then suddenly you have sudden degradation of ecosystems, such as ocean acidification and coral bleaching,” says Viglietti.
The same could be true of the oceans of the late Permian. Understanding what happened during the end-Permian mass extinction gives us clues about the rise of the dinosaurs – many of the ancient mammalian relatives died out, leaving ecological vacancies filled by dinosaur ancestors.
But the extinction of the end of the Permian also provides insight into the mass extinction Earth is currently undergoing as a result of climate change and habitat destruction.
“The environmental changes that we are causing and the impact we have on animal and plant species are reaching the point where the scale is so large that there is not really anything in human history that is comparable,” said Angielczyk.
“The fossil record can give us an idea of what huge biodiversity crises look like and how they unfold.” “It takes a long time to recover from extinction.
If we lose diversity, it will not recover in our lifetime, it will take hundreds of thousands or even millions of years, ” says Viglietti.“Studies like this show what our society should focus on.