Paleontologists have unearthed exquisitely preserved skulls and jaws, along with parts of the skull and jaws belonging to a previously unidentified species of Peilosaurus in Patagonia, Argentina.

Kostensuchus atrox roamed the Earth during the Cretaceous period approximately 70 million years ago.

This ancient species was a formidable predator, measuring about 3.5 m (11.5 feet) in length and weighing around 250 kg.

These animals featured broad, powerful jaws and large teeth capable of consuming substantial prey, including medium-sized dinosaurs.

Kostensuchus atrox was a member of the Peirosauridae family of crocodiles within the sub-order Notosuchia.

“This new species belongs to the notosuchian clade Peirosauridae, representing the latest and southernmost records of this crocodile-like group,” stated Dr. Fernando Novas, a paleontologist at Argentino de Ciencias Naturales ‘Bernardino Rivadavia.

The fossilized skulls and bones of Kostensuchus atrox were discovered in the Chorrillo Formation, approximately 30 km southwest of El Calafate in the province of Santa Cruz.

“The Chorrillo Formation dates back about 70 million years,” the paleontologist explained.

“At that time, southern Patagonia boasted a warm, seasonally humid environment filled with freshwater floodplain plants, home to dinosaurs, turtles, frogs, and various mammals.”

“The newly excavated fossils from this layer are almost complete, including skulls and jaws exhibiting visible details, along with multiple bones from the body.”

Kostensuchus atrox ranks as the second-largest predator identified in the Chorrillo Formation and likely served as one of the region’s top predators.

This new species is also the first crocodile-type fossil found in this geological layer and is among the most intact examples of a crocodilian ever discovered, offering scientists unique insights into these prehistoric creatures and their environments.

“The discovery of Kostensuchus atrox significantly enhances our understanding of the anatomy of the widely distributed Peilosaurus population, which was previously known from highly fragmented specimens found in South America and Madagascar,” the researchers noted.

“The new anatomical data illuminate both the similarities and distinctions between the extensive Peirosauridae and Baurosuchidae, other crocodile-like lineages that evolved independently into apex predators during the Cretaceous period in Gondwana.”

“Kostensuchus atrox provides insights into late Cretaceous ecosystems in southern Patagonia, which formed in freshwater habitats within warm climates, supporting diverse faunas of dinosaurs, mammals, and other vertebrates in a seasonally humid environment,” they added.

“The wide and tall snout of Kostensuchus atrox, particularly its robust forelimb anatomy, along with large, sturdy teeth and broad adductor chambers in the skull, suggests this new species was capable of overpowering substantial prey.”

“These characteristics indicate that Kostensuchus atrox occupied the role of the top predator within this ultimate Cretaceous ecosystem.”

The discovery of Kostensuchus atrox is detailed in a paper published this week in the journal PLOS 1.

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Fe Novas et al. 2025. A new large carbonized crocodile from the Maastrichtian in southern Patagonia, Argentina. PLOS 1 20(8): E0328561; doi: 10.1371/journal.pone.0328561