Crocodile-relative 'hypercarnivore' from prehistoric Patagonia was over 3 meters long and weighed 250 kilos

Stephanie Baum
scientific editor

Robert Egan
associate editor

A newly discovered species of a large, crocodile-relative predator has been described via a remarkably well-preserved fossil from Argentina, according to a study in PLOS One by Fernando Novas from Museo Argentino de Ciencias Naturales "Bernardino Rivadavia," Argentina, and colleagues.
The Chorrillo Formation formed around 70 million years ago, during the Maastrichtian age at the very end of the Cretaceous period. At this time, southern Patagonia was a warm, seasonally humid landscape of freshwater floodplains, home to creatures like dinosaurs, turtles, frogs, and various mammals.
The new fossil unearthed in this formation is largely intact, including a skull and jaws with visible details, as well as multiple bones from the body. This crocodile-like apex predator may have reached around 3.5 meters (11.5 feet) long and weighed around 250 kilograms (551 pounds), with a wide, powerful jaw and big teeth capable of devouring large prey—likely including medium-sized dinosaurs.
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Kostensuchus atrox—skull already prepared, freed from the rock. Credit: José Brusco, CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/) -
Kostensuchus atrox—Mounted skeleton (reconstructed 3D print and painted). Credit: José Brusco, CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)
The researchers named the species Kostensuchus atrox, referring to the Patagonian wind known in the Tehuelche native language as the Kosten and the Egyptian crocodile-headed god known as Souchos, with atrox meaning "fierce" or "harsh."
K. atrox itself was not a dinosaur, but rather a peirosaurid crocodyliform, an extinct group of reptiles related to modern crocodiles and alligators. This species is the second-largest predator known to scientists from the Maastrichtian Chorrillo Formation, and the researchers believe it was likely one of the top predators in the region.
K. atrox is also the first crocodyliform fossil found in the Chorrillo Formation, and one of the most intact peirosaurid crocodyliforms ever found, giving scientists unique new insights into these prehistoric animals and their ecosystem.
More information: Fernando E. Novas et al, A new large hypercarnivorous crocodyliform from the Maastrichtian of Southern Patagonia, Argentina, PLOS One (2025).
Journal information: PLoS ONE
Provided by Public Library of Science