The fossil shouldn’t have been there. The original bones of the black bear-size sabertooth predator, Inostrancevia, were found in northern Russia, encased in rocks more than 253 million years old. Yet paleontologists recently discovered the remains of the fearsome animal in the ancient rock of South Africa, thousands of miles away.
The story of how the long-fanged hunter arrived at such a distant location isn’t a tale of carnivorous success, but rather it highlights the last gasp of an animal fleeing the chaos of the worst mass extinction in Earth’s history. Sparked by ceaseless eruptions of the Siberian Traps, volcanoes in prehistoric Russia, the extinction event at the end of the Permian period wiped out some 70 percent of animal species on land.
It seems Inostrancevia migrated thousands of miles across the supercontinent Pangaea, heading south in search for more favorable hunting grounds. Described recently in the journal Current Biology, the fossils from the Karoo desert in South Africa were immediately recognizable as a sibling species to Inostrancevia from Russia. “Their identification was pretty straightforward,” says Field Museum paleontologist and study co-author Pia Viglietti, noting that the large size, relatively svelte proportions, and four upper incisor teeth all identify the animal.
Named as the new species Inostrancevia africana, the carnivore was a protomammal, or an animal more closely related to mammals than reptiles despite some reptile-like attributes. Looking at the rock layers where it was found, researchers detected a succession of different predators in a relatively short timeframe. Between about 259 and 253 million years ago, a similar predator called rubidgeines hunted in the region. Then the rubidgeines abruptly disappeared, replaced by Inostrancevia africana, itself going extinct by about 252 million years ago, only to be replaced by different predatory protomammals and early relatives of crocodiles.
“This is an incredible find,” says Loyola University Chicago paleontologist Megan Whitney, who was not involved in the new research. “Inostrancevia has long been considered endemic to Russian rocks, so to find this animal in the Karoo Basin of South Africa suggests a surprisingly large geographic distribution,” she says. Finding a new, huge species of protomammal in such a well-sampled area also hints that there are still important discoveries to be made in the region.
Predatory turnover
Amazing as it is that Inostrancevia africana lived in prehistoric South Africa, the animal didn’t stick around very long. Meat-eaters suddenly appearing only to go extinct is a sign of the drawn-out mass extinction. “The end-Permian extinction on land was actually more protracted than previously thought,” says Jennifer Botha, a co-author of the new study and paleontologist at the University of the Witwatersrand in Johannesburg. Life struggled against the changing conditions for as many as a million years.
“What was causing the rapid predator turnover was a global warming crisis,” Viglietti says. The erupting Siberian Traps poured out enough lava to bury a chunk of land the size of Illinois under 2,000 feet of molten rock. But more devastating to life was the release of a fantastic amount of carbon dioxide and other greenhouse gases into the atmosphere, distorting Earth’s climate and causing the relative amount of oxygen in the air to drop.
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On a rapidly warming planet where changes to temperature, rainfall, and aridity caused ecosystems to collapse, organisms had to either adapt or move to avoid extinction. “Environmental conditions changed from seasonally wet ecosystems to increasingly hot environments and what appear to be unpredictable swings between extreme droughts and flooding,” Botha says. Environments flipped so quickly and dramatically that many species had the ecological rug pulled out from under them.
“At the time Inostrancevia took over in South Africa as top predator, there were still large herbivores as a food source,” Viglietti says. The extinction of the earlier gorgonopsians provided an opening—but eventually changes to vegetation led to the extinction of the herbivorous prey animals, spelling the end for Inostrancevia, too.
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The discovery alters what experts thought about Earth’s worst ecological catastrophe. In the past, Whitney notes, paleontologists thought protomammals suffered dramatic losses and reptiles simply stepped in to fill the void in the Triassic period that followed. Finding multiple carnivores that tried to get a claw-hold before going extinct indicates “there were more complicated dynamics at play,” she says.
How to survive a mass extinction
Big carnivores didn’t fare well through the climate chaos. Most of life didn’t. “While the few million years where this faunal turnover took place seems like an insane amount of time to us, this is a blink of an eye in geologic time,” Whitney says. But some organisms managed to survive through the harsh conditions to reach the Triassic, when new ecosystems emerged as collections of “survivor species.”
“The Early Triassic survivors were able to survive constantly changing environmental conditions,” Botha says. “The quick and the dead, as it were.”
The most iconic survivor from the Permian is Lystrosaurus. The animal was a very different protomammal from Inostrancevia—and perhaps was even prey for the sabertooth. Lystrosaurus was a squat, beaked plant-eater that looked something like a pig with a turtle’s face. Their fossils are found in rocks dating from the close of the Permian through the beginning of the Triassic, carrying the protomammal legacy into the impending age of the dinosaurs.
Their success in the face of such adversity has repeatedly raised the same query among experts: How did Lystrosaurus survive what most could not?
The secret might be in the protomammal’s burrows. Lystrosaurus dug into the earth, hollowing out spaces of refuge in chaotic habitats. “Burrowing does appear to have been a very important factor, used either as a daily refuge, or to escape days-long bad weather conditions,” Botha says. The dog-size animal may have even used its burrows to hibernate through the worst seasons.
A “sleep or hide” response may have let Lystrosaurus and other burrowers make it through the worst. And other species likely used these shelters, too, meaning Lystrosaurus could have been a sort of ecosystem engineer, providing refuge from the harshness of the surface.
Lystrosaurus didn’t evolve the ability to burrow in response to the disaster. The protomammal could already do so, and burrowing offered an unexpected survival advantage. Most organisms that survived the mass extinction seem to have done so thanks to similar strokes of luck.
“For the survivors,” Viglietti says, “innate paleobiological traits likely allowed them to benefit from the conditions that caused mass extinction in other species.” The way organisms grew, grouped together, and reproduced all became critical factors for survival.
Our own ancestors were among the fortunate ones. The first mammals evolved from weasel-like protomammals called cynodonts that thrived in the Permian but were reduced to a few straggling branches in the Triassic. Burrowing, the ability to hibernate, and a broad tolerance for different environmental conditions, Viglietti says, likely allowed the cynodonts to make it through.
“This shows how lucky we are to even be here,” she adds. “Our mammal relatives got through this quarter-billion-year-old climate crisis by the skin of their teeth.”
