Flesh-Ripping Crocs Outlived Carnivorous Dinosaurs
Kostensuchus was a large carnivorous croc, estimated at about 12 feet in length. Art by Gabriel Diaz Yanten.
Maybe some dinosaurs survived into the “Age of Mammals.” In the decades before we understood what happened at the close of the Cretaceous, how a devastating asteroid impact forever changed our planet, it seemed reasonable enough that some dinosaurs, somewhere, had managed to hold out longer than the likes of T. rex and Triceratops. Blade-like teeth uncovered in South America suggested that the continent might have been such a refuge. Only carnivorous dinosaurs were known to have flattened, serrated, curved chompers, and several such teeth had been found in rocks that formed after they heyday of the dinosaurs.
In time, paleontologists realized that they were dealing with reptiles that broke the rules. The Cenozoic “dinosaur” teeth had not come from carnosaurs at all. Ancient crocodiles called sebecids had independently evolved teeth best-suited to slicing flesh, reptiles that had evolved alongside the non-avian dinosaurs and outlasted them.
Sebecus itself was named in 1937. It took paleontologists decades before they made the connection between such crocodiles and the mystery dinosaur teeth. Nearly a century later, we know that sebecids were impressive carnivores in their own right, snapping at small prey - including baby dinosaurs - in a world of giants. Paleontologist Fernando Novas and colleagues have just named another predator cut to this profile, Kostensuchus atrox.
At a glance, Kostensuchus is simply gorgeous. The first known fossil of the reptile includes a complete and articulated skull, as well as much of the spine, shoulder, hips, ribs, and several limb elements. It’s about as good a look at the 70 million-year-old croc as we could hope to get. The caudal bones are missing, but, based upon comparisons with related sebecids, Novas and colleagues expect Kostensuchus stretched about 12 feet from snout to tail tip.
Kostensuchus was big, even compared to its close relatives. Though the record of the smaller species is fragmentary, making comparisons challenging, Novas and coauthors estimate that Kostensuchus was about four times as massive as related crocs like Uberabasuchus and Lomasuchus. The larger size of the new croc, the researchers propose, is because the shift from being generalists to specialist carnivores required bigger bodies that could travel farther in a day and take on a broader range of Cretaceous morsels.
The fossil of Kostensuchus is one of the most complete of its kind ever found. José Brusco, CC-BY 4.0.
More impressive than the croc’s size, however, are the details of its predatory anatomy. The snout of Kostensuchus is about half of its total skull length, with large spaces for thick, powerful jaw-closing muscles. The reptile’s jaws are lined with large piercing and gripping teeth towards the front of the jaw, complemented with broad, slicing teeth behind. Altogether, the researchers write, the anatomy “results in a lengthening of the shearing edges whose primary functions are puncturing and slicing through the flesh of sizable prey.” Kostensuchus wasn’t an ambush predator waiting at the water’s edge. It was a terrestrial animal, trotting after prey that it gripped and grappled with impressively strong jaws.
Sebecids like Kostensuchus evolved their carnivorous abilities alongside non-avian dinosaurs. Somehow, they survived. Multiple Cenozoic sebecids have been found among the geologic layers of South America, among the continent’s apex predators during its millions of years of “splendid isolation.” In fact, some survived tantalizingly close in time to us. Some of the last sebecids managed to wind up on what are now Cuba, Puerto Rico, and the Dominican Republic, surviving there until about 5 million years ago - around the same time early humans were beginning to walk around eastern Africa.
Despite the fact that they’re long gone, I adore sebecids for what they remind us about the fossil record. The alligators and crocodiles we see around us today are not “living fossils.” They are part of a much broader, stranger family that has taken on many forms through hundreds of millions of years, their family’s evolution repeating certain beats. Semi-aquatic crocs have evolved multiple times, but so have predators that scampered over dry land to chase after dinosaurs, ancient mammals, and other creatures. Perhaps, if the reptilian family can persist for millions of years more, some of our modern crocodiles will emerge from the wetlands to stalk terrestrial prey once more.
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