The ‘Blessed Lizard’ That Inherited the Earth After Its Worst Apocalypse

Paleontologists in Argentina have discovered a deadly prehistoric crocodile with “blade-like serrated” teeth that triumphed over the Triassic some 237 million years ago, before large dinosaurs arrived and usurped the throne.

“We consider these as the apex predators of the Triassic,” says Ariel Cardillo, a doctoral candidate in vertebrate paleontology at Argentina’s National Scientific and Technical Research Council (CONICET) and lead author of the study. “They were really large animals compared to the rest of the ecosystem.”

From snarling snout to tail, the new species Shakajlura riojanensis would have been nearly 20 feet long. “This may not look like much, but in the Triassic, most of the fauna is pretty small,” Cardillo says. Shakajlura’s bite was likely as powerful as modern-day crocs, and every tooth was “like a knife pointing out of the mouth,” he adds.

Cardillo and his colleagues published their discovery earlier this summer in the journal Papers in Palaeontology.

Shakajlura also provides paleontologists with insight into a poorly understood period in Earth’s history when wildlife bounced back from “The Great Dying.” This cataclysmic event ended the Permian some 252 million years ago and is perhaps the largest mass extinction the planet has ever experienced.

“Terrestrial ecosystems are really starting to get back into where they were before the big extinction,” says Keegan Melstrom, a paleontologist at the University of Central Oklahoma who was not involved in the work. “If you survived this mass extinction, you basically get to inherit the Earth.”

A ‘Blessed Lizard’

In 2017, Cardillo’s colleagues were excavating a Late Triassic fossil deposit in the Chañares Formation in Argentina’s La Rioja province when they noticed part of an upper jawbone sticking out of the rock. They extracted it along with several more fossils and sent them to the La Plata Museum.

In total, the team had found skull bones, parts of the upper and lower jaws, a backbone, limb fragments, and an almost complete hip bone. Together, the fossils clued the team in that they had uncovered a paracrocodylomorph, an ancient cousin of crocodiles.

They chose the name Shakajlura riojanensis because it refers, in part, to the La Rioja province where the fossil was found. “Shakajlura” is a translation from Kakán, a language spoken by the Diaguita Indigenous people who live in the region, that means “blessed lizard.” The name references the rarity of the find—the last fossil from this group discovered in Argentina was described in 1997, nearly three decades ago.

Shakajlura likely used its dagger-filled jaws to chow on prey such as dicynodonts, large herbivores that were ungulate-like precursors of mammals. Since Shakajlura likely wasn’t aquatic—it took millions of years before crocodilians adapted to a more marine lifestyle— it may have used its legs and upright posture to chase down prey rather than relying on ambushing like its modern-day relative, says Cardillo. Dicynodonts, which lumbered around in herds, were likely easy targets for the carnivores, he adds. Though he notes that the team has not done a biomechanical analysis of how fast the croc could have run.

Melstrom says he was impressed with how big Shakajlura was. But he is cautious about making conclusions about how it hunted. He says some kind of ambush may have still played a role, like lions waiting in the grass.

“It’s certainly not a cheetah—it’s certainly not running things down,” Melstrom says, though he also doesn’t see it lying completely in wait as today’s crocodiles do, and speculates that they may have been capable of short pursuits.

Tyrants of a New Epoch

The biodiversity of the Early and Middle Triassic, from 252-237 million years ago, is less understood than in later periods because there are relatively few known fossil beds from these epochs. But these expanses of time are important to paleontologists because they represent a vast ecological change that occurred across the planet.

During “The Great Dying,” massive volcanic eruptions released carbon dioxide and sulfur dioxide, which choked the oxygen from the oceans. These changes wiped out most species on the planet, and it would take millions of years for the Earth’s biodiversity to begin recovering. At the start of the Triassic, most creatures had not reached anything near the sizes of the subsequent Jurassic and Cretaceous periods.

“The Triassic is a hard period to navigate,” Cardillo says. “We have this extinction—the End-Permian Mass Extinction—then we have a gap in our understanding of the ecosystems.”

The end of Shakajlura's reign is one of those gaps, Cardillo says, as he’s uncertain what spelled the creature's doom.

“These large ancestors are kind of an enigma—why they went extinct at the end of the Triassic,” he says. They may have had relatively small populations with big ranges spread out across the landscape, making them vulnerable to disturbance. Competition with early carnivorous dinosaurs might have also played a role, he says.

Regardless of how Shakajlura was overthrown, its discovery helps show that before big dinosaurs took over, crocodile-like creatures ruled parts of the planet. And their distant cousins—remnants of their once-great dynasty—survived and bit their way through all kinds of prey over the next 237 million years.

“This time," adds Melstrom, "represents a time period just before the birth of the modern world.”