An apex predator prowled the forests of Patagonia a few million years before the age of dinosaurs came to an end. As large as a Siberian tiger, it padded on four legs, with powerful jaws and teeth the shape of steak knives.
But this hunter was no dinosaur. In a paper published on Wednesday in the journal PLOS One, researchers announced the discovery of Kostensuchus, a large, land-dwelling crocodile. The find shows that predatory dinosaurs in South America faced stiff competition from their crocodilian cousins well into the last days of their reign.
“They were not only abundant,” said Fernando Novas, a paleontologist at the Bernardino Rivadavia Natural Sciences Argentine Museum and an author of the paper; they were also large enough to fight dinosaurs like megaraptors and dromaeosaurs over prey.
The remains of the ferocious crocodile were discovered in March 2020 in Santa Cruz, a province in Argentina. The cold, windswept rocks there formed six million years before the end of the Cretaceous period, Dr. Novas said. He and colleagues had already found traces of a long-necked dinosaur and long-armed, hook-clawed predatory dinosaurs there. While walking the plains, members of the expedition noticed a heavy block of rock containing hints of a crocodilian skull.
The remains belonged to a lineage of terrestrial crocodiles known as pierosaurids, which tend to have extraordinarily incomplete remains, said Cecily Nicholl, a specialist on land crocodiles at University College London who was not involved in the study. But when the specimen was fully prepared months later, it was surprisingly well preserved, with a skull that was attached to an articulated spine, shoulders and hips.
Based on comparisons with living crocodilians, the complete animal would have been around 11½ feet long and weighed 551 pounds, the team estimated. While the animal was smaller than the largest contemporary crocodiles, its wide, powerful jaws and long, flat, serrated teeth were comparable to those of a big predatory dinosaur or a modern Komodo dragon. They would have been adept hunters, including of medium-size dinosaurs.
While North America and Asia had their share of Cretaceous crocodiles, they were mostly from families that had evolved a semiaquatic lifestyle. But crocodiles took a different trajectory in South America and Africa, where several families walked with their limbs held under their bodies — like mammals and dinosaurs — rather than with the sprawling stance of their water-loving cousins.
The team’s analysis of Kostensuchus’s hips suggested that it held its legs in slightly more of a sprawl than some related land crocs, suggesting that, while it was a capable land predator, it and other pierosaurids might have been relatively comfortable in water.
That points to the possibility that different families of crocodilians might have independently evolved toward more aquatic lifestyles multiple times, Dr. Novas said.
Skeletal anatomy alone makes it difficult to tell whether an animal like Kostensuchus spent much time in the water, or whether it was a land-dwelling member of an increasingly aquatically inclined family, said Jeremy Martin, a paleontologist at the University of Lyon in France who was not involved with the study. Dr. Martin suggested that a study of the stable isotopes within the bones, which have been used to help pinpoint diet and climatic conditions in fossil animals, could reveal more about the newly discovered crocodilian’s lifestyle and environment.
Dr. Martin also said that the team might have overestimated the animal’s body length, noting that the researchers’ suggested proportions might not match other — admittedly more fragmentary — specimens.
Either way, Kostensuchus was larger than many other pierosaurids, and, as the southernmost and latest-known member of the group, it fills an important gap in their family tree, Dr. Novas said.
It also shows that terrestrial crocodiles of different lineages regularly became large enough to challenge big predatory dinosaurs across South America, an ecological dynamic that would linger even after each group lost a majority of its species in the Cretaceous extinction. As recently as 20 million years ago, enormous land crocodiles still competed with large terror birds across the South American plains.
In a world of running crocodiles of every size, Dr. Novas said, Kostensuchus and its later cousins were equivalent to lions.
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