The end-Cretaceous was the age of the dinosaurs, an era populated by iconic prehistoric creatures like Ankylosaurus, Gallimimus, Triceratops, and Tyrannosaurus rex. Our favorite dinosaurs might be the subject of toys, lunch boxes, and blockbuster movies, but they weren’t alone.
Dinosaurs shared the landscape with other creatures both big and small, including oversized croc-like predators with a taste for dino meat. Information about these ancient reptiles has been sparse because their fossil records are incomplete. Most of what was known came from fragmented remains, mostly partial mandibles, of other broad-snouted peirosaurids (a family of crocodile relatives which lived on the Gondwana supercontinent before the asteroid hit).
Now, a paper published in the journal PLOS One describes the discovery of one of the most well-preserved and informative peirosaurid crocodyliform fossils ever found.
K. atrox, the crocodile-like hypercarnivore that ate dinosaurs
Figure 5 KOSTENSUCHUS ATROX
The new species, dubbed Kostensuchus atrox was found in Argentine Patagonia, about 18 miles southwest of El Calafate. The formation dates to the late Cretaceous, about 70 million years ago and features a wide variety of plant and animal fossils. Paleontologists uncovered the skull, jaws, and partial skeleton of K. atrox from a large rock concretion.
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The startling completeness of the fossil revealed many features of broad-snouted peirosaurids for the first time. The specimen features large ziphodont teeth (laterally compressed, curved teeth with serrated edges), a broad oreinirostral (tall and domed) that’s slightly longer than half the skull length, and skull features that suggest the presence of powerful temporal muscles. K. atrox was built for biting.
Figure 4 KOSTENSUCHUS ATROX
The fossil beds where K. atrox was found are a particular favorite of paleontologists because they reveal the complexity of the end-Cretaceous ecosystem. Over the years, researchers have dug up pollen, fungal spores and other plant remains, fish, frogs, turtles, mammals, and reptiles. The dinosaurs uncovered from this site include large titanosaurs, the terrifying Maip macrothorax, parankylosaurs, hadrosaurs, and more.
Even in that crowded ecosystem, K. atrox practically ruled the roost. It weighed in at 550 pounds and stretched nearly 12 feet from tip to tail. While some of the limbs and tail were missing from the fossil, scientists were able to estimate the length and weight by comparing the fossil to the skeletons of living relatives like caimain and alligators. While some modern crocodilians are larger, it was enough for K. atrox to carve out a space in the Patagonian late Cretaceous. Among known predators in the region at the time, only Maip was larger.
Figure 6 – KOSTENSUCHUS digital reconstruction
Researchers note that this size expansion from more diminutive ancestors aligns with a wider trend in notosuchian clades (a subset of the Gondwanan crocodylomorphs) which got larger throughout the Cretaceous. The size upgrade has been linked with a transition from an omnivorous diet to a hypercarnivorous lifestyle. By 70 million years ago, K. atrox had grown comparatively huge and ascended to apex predator status, snacking happily on anything it could get its jaws around.
Its size, combined with those long, serrated teeth gave K. atrox the ability to puncture and rip through the flesh of larger prey including the medium-sized dinosaurs of the day.
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