prehistoric turtle Laurasichersis relicta
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Credit: José Antonio Peñas

It's now extinct, but how did this prehistoric turtle survive what killed the dinosaurs?

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Feb 7, 2020

Who thought that one of the survivors of the killer asteroid that head-butted Earth 66 million years ago and wiped out monster reptiles like T.rex would be ... a turtle?

Laurasichersis relicta may now be extinct, but it somehow managed to survive an event that sent temperatures soaring and then plummeting after ash from the collision blocked sunlight and heat, causing a nuclear winter effect that is thought to have killed off at least 70% of organisms on Earth. Unearthed in what was once the continent of Laurasia, the fossil of this prehistoric terrestrial turtle has now been found to be the only terrestrial turtle that survived the die-off in the Northern Hemisphere. It also had advantages that even dinosaurs couldn’t compete with.

“No [prehistoric turtle] has been described in [Laurasia],” said paleontologist Adán Pérez García in a study recently published in Scientific Reports, adding that the only survivors were "exclusive to southern Gondwana." 

Laurasia and Gondwana were the two immense subcontinents that split from the initial supercontinent of Pangea. Laurasia, the northernmost half, included most of what are now Europe and Asia. The L. relicta holotype (only specimen known to exist so far) that is thought to have originated in China and Mongolia and emerged in France, was the only terrestrial turtle in the Northern Hemisphere to survive the Cretaceous-Paleogene mass extinction that claimed not only the dinosaurs but almost all the early turtle species that also roamed the planet. So what spared this one from being obliterated?

L. relicita was a meiolaniid, or horned turtle. Meiolaniids were the only primitive turtle species that held on to life in Gondwana, but L. relicta was the sole survivor in Laurasia. It had some pretty rad body armor that made up for its inability to hide out from predators by retracting its neck. Instead, it developed scary defensive spikes linked together on its neck, legs, and tail. The 23-foot shell that acted as its built-in shield was made up of no more plates than you would find in a modern turtle, but the underside had more than had ever been found in any other turtle species.

That ridiculously hard armor probably made L. relicta much less appetizing to predators, since it must have been a horror for even dino dagger teeth to chew.

Even the toughest turtle in Laurasia eventually succumbed to extinction. There is no way it would have survived without food, and at least some of its food sources must have been wiped out by the initial asteroid crash. Maybe not enough were left to sustain the population long enough. Shifts in dominant species couldn't have helped, either. Though most of those fearsome carnivorous dinosaurs were wiped out, that only left spaces to be filled higher up in the food chain, and with the evolution of meat-eating mammals that kept getting larger and more threatening along with their teeth, it started to disappear.

Ultimately, though, scientists are still trying to unravel all of the answers. "The reason why Laurasichersis survived the great extinction, while none of the other primitive North American, European or Asian land turtles managed to do so, remains a mystery," Pérez García admitted in a press release.

Maybe more of the secrets it’s been hiding in its shell will emerge if and when more specimens crawl out of wherever they are hiding.

(via Scientific Reports)

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