As apex predators of the Cretaceous period go, Tyrannosaurus Rex is pretty iconic. And yet, it's likely even formidable tyrant-lizards would have watched their steps around Deinosuchus - North America's so-called "terrible crocodile."
During the heyday of Deinosuchus, adults of the aquatic ambush predator were among the largest carnivores in their ecosystems. The enormous Tyrannosaurus rex was over five million years off, and the tyrannosaurs of the time were not quite so long or bulky. (Teratophoneus, found in southern Utah among strata that also yield Deinosuchus, was about twenty feet long, and Daspletosaurus from Montana grew to be about thirty feet long.) A fully mature Deinosuchus would have outstretched and outweighed the dinosaur competition, and would have undoubtedly been a deadly apex predator in the water habitats it haunted.
The skull of Deinosuchus testifies to its destructive potential. The alligatoroid's skull was large, broad, and equipped with an array of teeth deployed to pierce and crush. Indeed, even though there were other giant crocodylomorphs of near-equal size during the Mesozoic (such as the narrow-snouted Sarcosuchus), Deinosuchus appears to be unique in having the anatomical necessities to take down hadrosaurs and other unwary dinosaurs at the water's edge.
Granted, much like like T. Rex, paleontologists aren't entirely sure whether Deinosuchus was exclusively an active predator, a scavenger, or some combination thereof. Then again, would knowing that this 40-foot-long, sickle-toothed behemoth was a "scavenger" make you any more inclined to loiter anywhere near the remote vicinity of its jaws? We didn't think so.
Read more about Deinosuchus over at Dinosaur Tracking.