A new crocodile that lived alongside the last dinosaurs has been discovered in Argentina

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Paleontologists from CONICET, in Argentine, discovered fossil remains that allow us to understand the ecosystem that thrived in southern Patagonia before the end of the “Age of Dinosaurs.” The research also received funding from institutions in Brazil and National Geographic.

Kostensuchus Skeleton. Image credit: José Brusco

An interdisciplinary team of specialists from CONICET discovered a large part of the skeleton, including the skull and jaws, of a large crocodile that lived in southern Argentina 70 million years ago, in rocks from the Chorrillo Formation. The site of the discovery, described in the scientific journal PLoS ONE, is located about 30 km south of the town of El Calafate, in the southwest of the province of Santa Cruz. The researchers named the new animal Kostensuchus atrox, which means “fierce crocodile referring to the south wind.”

As the scientists explained, their habits were predatory and they belong to an extinct family of crocodiles (the peirosaurs), which evolved in South America and Africa during the Cretaceous Period. Unlike living crocodiles, the head of Kostensuchus was proportionally high, with eyes oriented outward and nostrils projected forward, indicating that it did not have the aquatic habits of its living relatives (with flattened skulls, eyes, and nostrils projected upward).

“Kostensuchus atrox reconstruction carried out by Gabriel Díaz Yanten. Photo: courtesy of researchers.”

“This new species is distinguished from all previously known species by characteristics such as the large size of its teeth and skull, the robustness of its jaw, and the large size of the cavities where the muscles responsible for the bite were located. These characteristics are what lead us to interpret it as a top predator of the ecosystem,” comments Diego Pol, a researcher at CONICET in the Argentine Museum of Natural Sciences “Bernardino Rivadavia” (MACN-CONICET).

The characteristics of the rocks and other paleontological remains found with its skeleton indicate that Kostensuchus roamed humid environments with lush vegetation. His body was robust and the legs, relatively short, were positioned vertically under the body, which allowed him to move with greater agility than a modern caiman or crocodile, whose legs are oriented outward and are more prone to crawling.

The head of Kostensuchus measured 50 centimeters long, being proportionally large compared to the rest of the body, becoming the “bulldog” of crocodiles. The snout was armed with more than 50 teeth, some of which were over 5 centimeters tall. The edges of the teeth are serrated, which increased the cutting ability of the flesh of its victims. The jaws were powered by powerful muscles that gave it a quick and extremely strong bite.

These anatomical features were key to interpreting the ecological role of Kostensuchus as one of the main predators of the late Cretaceous in Patagonia. “Another of the predators we have discovered in these rocks is the dinosaur Maip macrothorax (a carnivorous predator that was one of the last dinosaurs before extinction), a close relative of the Megaraptor from Neuquén. It is very likely that Kostensuchus and Maip competed for food, similar to the confrontations that occur today in Africa between hyenas and lions” says paleontologist Fernando Novas, researcher at CONICET in the Félix de Azara Foundation for Natural History and first author of the paper.

The finding
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Since 2019, this Patagonian region has been the subject of explorations led by Novas and his colleague Makoto Manabe from the National Museum of Tokyo, Japan, and their respective workgroups. “From the very first moment, we were able to appreciate the vast fossil potential that this area of our country has. The rocks that contain the fossils are called the Chorrillo Formation, and their age is around 70 million years,” Novas clarifies.

Over the course of the expeditions, a large amount of material was collected, including bones of giant dinosaurs, both herbivorous and carnivorous, fossils of other animals such as insects, frogs, fish, turtles, snakes, teeth of small mammals, terrestrial and aquatic snails, and plant remains. “It gave us a general framework of what the environment was like, of what the different components of an ancient ecosystem that existed in southern Argentina immediately before the extinction of the dinosaurs were like,” emphasizes Federico Agnolín, a researcher at CONICET in MACN-CONICET and co-author of the work.

The dinosaurs discovered there include the great predator Maip macrothorax, and the herbivores Nullotitan glaciaris, nearly 25 meters long, and Isasicursor santacrucensis, the size of a guanaco. Now a robust crocodile, nearly 3 meters long, is added to the list of reptiles, and its powerful jaws indicate that it could confront a Maip as well as capture some of the contemporary herbivorous dinosaurs.

The south of Patagonia, where the Kostensuchus atrox campaign took place. Photo: courtesy of researchers.

The discovery of this crocodile occurred on March 10, 2020, just before the onset of the COVID-19 pandemic. The working group consisted of 25 Argentinians, including paleontologists, technicians, and interns, and five Japanese researchers. The camp was located high up in the mountain, although it provided the best amenities to endure the low temperatures, rain, and wind that prevail in this part of Patagonia. Two of its members, Marcelo Isasi, a technician at CONICET in MACN-CONICET, and Gabriel Lio, a paleoartist, stopped their march in the bed of a dry river with huge stones, in order to wait for the rest of the team and begin the retreat to the camp, and during the wait, they found bones of a complete fossilized skull. In the following days, the researchers focused on fitting and gluing the scattered blocks, thus reassembling the puzzle of bones. “We were able to verify that this sequence of blocks contained the almost complete skeleton of an animal unknown to science,” explains Novas.

“Marcelo Isasi and Fernando Novas, alongside the Kostensuchus atrox crocodile bones. Photo: courtesy of the researchers”

Then, during the coronavirus pandemic, Isasi dedicated almost six months of intense work. “With the help of high-precision pneumatic hammers, I was exposing the bone, and as the teeth began to appear, I couldn’t believe it: they were very large and shiny, and had serrated edges. My curiosity about what kind of animal was trapped in the rock was overwhelming, so the workday stretched from early in the morning until the early hours of the next day. I couldn’t stop working,” Isasi recalls. Once the pandemic was over, and after the bones were freed from the rock, the researchers were surprised to find that it was a new species of crocodile measuring just over three meters long, and that its skull and jaws were almost completely preserved.

It should be noted that the study of Kostensuchus also involved Makoto Manabe and Takanobu Tsuijishi from Japan and Ismar de Sousa Carvalho from Brazil, a specialist in Mesozoic crocodiles. Additionally, to conduct the research, the scientists received funding from the National Geographic organization, the Carlos Chagas Filho Foundation for Research Support of the State of Rio de Janeiro (FAPERJ), and the National Council for Scientific and Technological Development (CNPq) of Brazil."

Citation
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The paper A new large hypercarnivorous crocodyliform from the Maastrichtian of Southern Patagonia, Argentina was published in PLoS ONE. Authors: Fernando E. Novas, Diego Pol, Federico L. Agnolín, Ismar de Souza Carvalho, Makoto Manabe, Takanobu Tsuihiji, Sebastián Rozadilla, Gabriel L. Lio & Marcelo P. Isasi.

A new large hypercarnivorous crocodyliform from the Maastrichtian of Southern Patagonia, Argentina Fernando E. Novas,Diego Pol ,Federico L. Agnolín,Ismar de Souza Carvalho,Makoto Manabe,Takanobu Tsuihiji,Sebastián Rozadilla,Gabriel L. Lio,Marcelo P. Isasi Published: August 27, 2025 https://doi.org/10.1371/journal.pone.0328561