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Did giant crocodiles once rule territories where we thought predatory dinosaurs were king?

File:Sarcosuchus Paris.jpg
Sarcosuchus, a giant crocodile, 110 mya/David Craven, Paris Musseum

Maybe. In a somewhat contrarian view of the dinosaurs, an Economist writer advises, “Old crocs: Even in their heyday, dinosaurs were not quite as dominant as popular myth makes them out to be” (Nov 12th 2011),

That the past role of crocodiles (or, strictly, crocodilians, since they came in many sizes and shapes, not all of which resemble the modern animals) has been underestimated was suggested a few years ago by Paul Sereno. Dr Sereno, a palaeontologist at the University of Chicago, uncovered a crocodile-dominated ecosystem from about 100m years ago (the middle of the Cretaceous period), in what is now north Africa. Besides water-dwelling giants similar to (though much bigger than) today’s animals, he found a range of forms including vegetarians and species that ran on elongated legs—more like dogs than crocodiles.

One problem was, why did the dinosaur trackway that runs through Colorado, New Mexico, Kansas, and Oklahoma show no evidence of large carnivorous dinosaur predators. What if the largest predators were not in fact dinosaurs?

And, when Dr Lockley and Dr Lucas re-examined the tracks they found that that was exactly what was going on. Instead of theropod footmarks, they found those of crocodilians. More than a quarter of the places where the dinosaur freeway surfaces have yielded signs of crocs. And they were big: sometimes more than four metres long. That is certainly large enough to take on an adult ornithopod.

Such megacrocs, then, could easily have acted as top predators in this ecosystem. But that does not completely explain the absence of theropod tracks.

The researchers point out that these areas were marshy back then, and that crocodilians would be much better suited to that than therapods. Interesting.

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