In prehistoric Patagonia tens of millions of years ago, a fierce reptile stalked the land. It wasn’t a dinosaur—but it hunted them.
Scientists have discovered a remarkably well-preserved skeleton of a new 3.5-meter-long reptile with sharp, blade-like teeth and a skull built for crushing. It belonged to a now-extinct group of crocodile relatives called peirosaurids, and the find is reshaping what we know about top predators in South America at the end of the Cretaceous.
Scientists named the species Kostensuchus atrox, combining “Kosten,” the Aonikenk word for Patagonia’s fierce winds, with “atrox,” the Latin word for harsh or fierce. It’s the most complete fossil of its kind ever found.
A Dinosaur Eating Croc
Unearthed near El Calafate in Argentina’s Santa Cruz province, the fossil includes a nearly complete skull, jaws, and a good portion of the body. It dates back to the Maastrichtian age, about 70 million years ago—just before the asteroid hit.
“This specimen is one of the best preserved and anatomically informative peirosaurid crocodyliform yet recorded, and the most complete representative of robust, broad snouted members of this clade,” the study’s authors wrote in PLOS ONE, led by Fernando Novas of the Museo Argentino de Ciencias Naturales.
But this was no swamp ambusher like today’s crocodiles. Kostensuchus atrox was built for land. It featured strong shoulders, a compact but heavy skull, and teeth adapted to slicing through flesh. It was what paleontologists call a “hypercarnivore,” meaning an animal that fed almost exclusively on meat. And in this case, its prey likely included medium-sized dinosaurs, which shared its ecosystem.
What Makes Kostensuchus Special?
Peirosaurids, while related to modern crocs and alligators, were a wildly different branch on the reptilian tree. They lived only during the Cretaceous and thrived across South America, Africa, and Madagascar. Their evolutionary branch died out, while the ancestors of today’s crocs survived the mass extinction that wiped out the dinosaurs. Until now, most had been described from fragments—a tooth here, a bit of jaw there. The new Kostensuchus specimen finally changes that.
Its short, deep snout and blade-like ziphodont teeth, complete with serrated edges for cutting, set it apart. Unlike the long, thin snouts of modern fish-eating crocs, this one’s skull was thick and wide. The scientists compared it to a powerful wedge: capable of immense bite force and rapid shearing.
The fossil also shows a broad scapula and a robust humerus, signs of strong forelimbs. That, combined with its cranial features, strongly suggests this was a predator that wrestled its prey to the ground.
Patagonia Before the Purge
The fossil was found in the Chorrillo Formation, a layer of rock that has recently become a treasure trove for paleontologists. This region once teemed with life: dinosaurs like the titanosaur Nullotitan, the predatory Maip, birds like Kookne, early mammals, and now—crocodyliforms.
Until now, paleontologists have found no crocodyliform fossils in this part of the formation. Kostensuchus fills that gap. Its discovery shows that crocodyliforms were competing with theropod dinosaurs for predatory niches—and thriving.
The team conducted a detailed phylogenetic analysis—a family tree—and placed Kostensuchus in a new broad-snouted clade of peirosaurids, alongside other poorly known genera like Colhuehuapisuchus from Patagonia and Miadanasuchus from Madagascar.
A Legacy in Stone
Kostensuchus atrox is proof that top predators in the Cretaceous weren’t all dinosaurs. This powerful crocodyliform carved out its own place in the food chain, competing in a landscape filled with giants.
Preserved in the sediments of Patagonia, Kostensuchus gives us a rare look at one of the last land predators before the mass extinction.
“The new anatomical information provided by Kostensuchus,” the scientists wrote, “sheds light on both the similarities and differences between broad-snouted peirosaurids and baurusuchids, the other crocodyliform clade that independently evolved into apex predators during the Cretaceous of Gondwana.”
