Paleontologists have unearthed a beautifully preserved skull and jaws as well as part of the postcranial skeleton of a previously unknown peirosaur species in Patagonia, Argentina.
Life reconstruction of Kostensuchus atrox. Image credit: Gabriel Diaz Yanten.
Kostensuchus atrox roamed Earth during the Maastrichtian age of the Cretaceous period, around 70 million years ago.
The ancient species was a large predator, approximately 3.5 m (11.5 feet) long and 250 kg in weight.
The animal had a wide, powerful jaw and big teeth capable of devouring large prey, likely including medium-sized dinosaurs.
Kostensuchus atrox belonged to Peirosauridae, a Gondwanan family of crocodylomorphs within the suborder Notosuchia.
“This new species belongs to the notosuchian clade Peirosauridae, representing the latest and southernmost record for this group of crocodyliforms,” said Dr. Fernando Novas, a paleontologist at the Museo Argentino de Ciencias Naturales ‘Bernardino Rivadavia,’ and his colleagues.
The fossilized skull and bones of Kostensuchus atrox were found in the Chorrillo Formation, about 30 km south-west of the town of El Calafate in the province of Santa Cruz.
“The Chorrillo Formation formed around 70 million years ago,” the paleontologists said.
“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.”
Kostensuchus atrox is the second-largest predator known to scientists from the Chorrillo Formation, and was likely one of the top predators in the region.
The new species is also the first crocodyliform fossil found in this formation, and one of the most intact peirosaurid crocodyliforms ever found, giving scientists unique new insight into these prehistoric animals and their ecosystem.
“The discovery of Kostensuchus atrox considerably expands the knowledge about the anatomy of broad-snouted peirosaurids, previously known from extremely fragmentary remains from South America and Madagascar,” the researchers said.
“The new anatomical information 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.”
“Kostensuchus atrox formed part of the latest Cretaceous ecosystem of southern Patagonia, in a freshwater ecosystem under a temperate to warm climate with seasonal humidity, alongside a diverse fauna of dinosaurs, mammals, and other vertebrates,” they added.
“The broad and high snout of Kostensuchus atrox, with notably large and robust ziphodont teeth, along with a broad adductor chamber in the skull and deep mandibular ramus, and robust forelimb anatomy suggests that the new species was capable of subduing large prey.”
“These features imply that Kostensuchus atrox played the role of a top predator within this end-Cretaceous ecosystem.”
The discovery of Kostensuchus atrox is described in a paper published this week in the journal PLoS ONE.
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F.E. Novas et al. 2025. A new large hypercarnivorous crocodyliform from the Maastrichtian of Southern Patagonia, Argentina. PLoS One 20 (8): e0328561; doi: 10.1371/journal.pone.0328561